crcbl-shell 0.14.0

//! Hand-written FFI to `user32`, `gdi32`, `shcore`, `shell32`, `imm32`,
//! `dwmapi` and `kernel32`, and the wire structures the Win32 backend passes
//! across it.
//!
//! # Decision: `#[link]`, not `dlopen` — the opposite of the two Linux backends
//!
//! `x11::ffi` and `wayland::ffi` both load their libraries with `dlopen`, and
//! both state the same reason: the registry in [`backend`](crate::backend) is a
//! fall-through list, so an entry has to be able to fail at *runtime*. A
//! `DT_NEEDED` on `libwayland-client.so.0` kills the process in `ld.so` before
//! [`open`](crate::open) runs, on any machine that does not have it — and a
//! machine without libwayland is an ordinary machine.
//!
//! **That premise does not hold here, and the asymmetry is deliberate rather
//! than an oversight.** `user32.dll`, `gdi32.dll`, `shell32.dll`, `imm32.dll`
//! and `kernel32.dll` are part of the operating system: a Windows that lacks
//! them is not a Windows this engine failed to support, it is a Windows that
//! cannot run any process at all. `shcore.dll` ships with every Windows since
//! 8.1 and `dwmapi.dll` with every one since Vista, both below this backend's
//! floor. There is nothing for a runtime
//! probe to discover, and `LoadLibraryW` + `GetProcAddress` for the system
//! libraries would buy exactly one thing: a fallible code path with no failure.
//!
//! The registry consequence is the one that matters and it is satisfied:
//! Windows has a single backend, so there is no fall-through to protect. If a
//! second Windows backend is ever added, the entry that must be able to fail is
//! *that* one.
//!
//! # Decision: Windows 10 version 1607 is the floor
//!
//! Set by DPI, not by anything else here. The windowing rules in
//! `docs/notes/backends.md` require
//! "one `scale_factor` concept over … per-monitor-v2 (Windows)", and the three
//! APIs that make per-monitor DPI work — `SetProcessDpiAwarenessContext`,
//! `GetDpiForWindow` and `AdjustWindowRectExForDpi` — all arrive in 1607.
//! `GetPointerType` and the `WM_POINTER*` messages are Windows 8, below the
//! floor; everything else this module declares is Windows XP-era.
//!
//! One wrinkle is worth stating rather than discovering: the *awareness context
//! value* [`DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2`](value::DPI_PER_MONITOR_AWARE_V2)
//! is documented from 1703, one release after the function that takes it. On a
//! 1607 host the call therefore fails with `ERROR_INVALID_PARAMETER` instead of
//! being missing, which is why
//! `shell::set_dpi_awareness` inspects
//! `GetLastError` rather than treating a `FALSE` return as fatal. Below 1607
//! the process fails to *start*, in the loader, exactly as the Linux backends'
//! `dlopen` argument predicts — and that is the price of linking, paid
//! knowingly on a platform where the libraries cannot be absent.
//!
//! # What is deliberately not declared
//!
//! | Not used | What it would buy | Why not |
//! | --- | --- | --- |
//! | `EnumDisplayDevicesW` | a monitor's marketing name | it usually answers "Generic PnP Monitor", which is worse than the device name for telling two displays apart |
//! | `ToUnicode` | the character a key produces | it **consumes** dead-key state, so calling it would eat the accent `WM_CHAR` was about to deliver. [`MapVirtualKeyW`] with `MAPVK_VK_TO_CHAR` answers the same question without side effects |
//! | `GetAsyncKeyState` | modifier state | it reads the hardware *now*, not at the message's time. [`GetKeyboardState`] is the snapshot that belongs to the message being processed |
//! | `RegisterDragDrop` and `IDropTarget` | drag *feedback* — a drop cursor, hover highlighting, non-file formats | it is COM: `OleInitialize`, a hand-written vtable, `IUnknown` reference counting and an apartment this crate does not own. `WM_DROPFILES` delivers the file paths the seam asks for; see `win32::dnd` for the whole comparison |
//! | `SetClipboardData` with a null handle | delayed rendering — claim the format now, produce the bytes when asked | the owner must answer `WM_RENDERFORMAT` **synchronously, from the window procedure**, and this backend's procedure records rather than acts for the reason its own docs give. See `win32::clipboard` |
//! | `AddClipboardFormatListener` | a "the clipboard changed" event | the seam has no such event, and a backend that invented one would be the only implementation of it |
//! | `SetTimer` | a frame during a modal resize loop | see the `win32` module docs — it needs a callback the seam does not have |

#![allow(non_snake_case)]

use core::ffi::c_void;

// ---------------------------------------------------------------------------
// Scalar aliases
// ---------------------------------------------------------------------------

/// Every Win32 handle this backend touches: `HWND`, `HINSTANCE`, `HMONITOR`,
/// `HCURSOR`, `HBRUSH`, `HMENU`, `HDC`.
///
/// One alias rather than a newtype per kind, for the reason the X11 backend
/// uses one `Cookie` for every `xcb_*_cookie_t`: they are the same thing on the
/// wire, and the type system cannot check which one a message actually carried.
/// Where a distinction matters it is in the parameter name.
pub type Handle = *mut c_void;

/// `WPARAM`.
pub type Wparam = usize;
/// `LPARAM`.
pub type Lparam = isize;
/// `LRESULT`.
pub type Lresult = isize;
/// `BOOL` — zero is false, anything else is true. **Not** `bool`: Win32
/// functions return `TRUE` as `1` but callbacks may return any non-zero value,
/// and `bool` has exactly two valid bit patterns.
pub type Bool32 = i32;

/// `WNDPROC`.
pub type WindowProc = unsafe extern "system" fn(Handle, u32, Wparam, Lparam) -> Lresult;

/// `MONITORENUMPROC`.
pub type MonitorEnumProc = unsafe extern "system" fn(Handle, Handle, *mut Rect, Lparam) -> Bool32;

/// `ENUMRESNAMEPROCW`: one resource's name, which is an integer id in the low
/// word when its high bits are zero and a NUL-terminated string otherwise.
pub type EnumResNameProc =
    unsafe extern "system" fn(Handle, *const u16, *mut u16, Lparam) -> Bool32;

// ---------------------------------------------------------------------------
// Structures
// ---------------------------------------------------------------------------

/// `RECT` — left, top, right, bottom, and the right/bottom edges are
/// **exclusive**.
///
/// The single most common Win32 mistake is treating it as a position and a
/// size; it is two corners, and `GetClientRect` always answers with a zero
/// origin.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct Rect {
    /// Left edge, inclusive.
    pub left: i32,
    /// Top edge, inclusive.
    pub top: i32,
    /// Right edge, exclusive.
    pub right: i32,
    /// Bottom edge, exclusive.
    pub bottom: i32,
}

impl Rect {
    /// Width, clamped at zero — a rectangle whose right edge is left of its
    /// left one is degenerate rather than negative-width.
    pub const fn width(self) -> i32 {
        if self.right > self.left {
            self.right - self.left
        } else {
            0
        }
    }

    /// Height, on the same terms as [`width`](Self::width).
    pub const fn height(self) -> i32 {
        if self.bottom > self.top {
            self.bottom - self.top
        } else {
            0
        }
    }

    /// The overlap of two rectangles, degenerate when they do not touch.
    ///
    /// Here because **`ClipCursor` intersects with the virtual screen** before
    /// applying: a window wider than the desktop gets a clip narrower than its
    /// client area, and nothing reports that it happened. A test that asserts
    /// the clip equals the client rectangle is therefore asserting something the
    /// API does not promise; one that asserts it equals this is asserting what
    /// it does.
    ///
    /// Test-only, because the backend never has to compute the clamp — the
    /// system applies it — and only a test has to *predict* it.
    #[cfg(test)]
    pub const fn intersect(self, other: Self) -> Self {
        let left = if self.left > other.left {
            self.left
        } else {
            other.left
        };
        let top = if self.top > other.top {
            self.top
        } else {
            other.top
        };
        let right = if self.right < other.right {
            self.right
        } else {
            other.right
        };
        let bottom = if self.bottom < other.bottom {
            self.bottom
        } else {
            other.bottom
        };
        Self {
            left,
            top,
            right,
            bottom,
        }
    }
}

/// `APPBARDATA`: what every `SHAppBarMessage` call reads and writes.
#[repr(C)]
#[derive(Clone, Copy, Debug)]
pub struct AppBarData {
    /// The structure's own size, which the shell checks.
    pub cb_size: u32,
    /// The appbar's window.
    pub hwnd: Handle,
    /// The message the shell sends the appbar its `ABN_*` notifications in.
    pub callback_message: u32,
    /// An `ABE_*` edge.
    pub edge: u32,
    /// The appbar's rectangle, in desktop pixels.
    pub rc: Rect,
    /// Message-specific.
    pub l_param: Lparam,
}

impl AppBarData {
    /// One for `hwnd`, with every other field zero.
    pub fn new(hwnd: Handle) -> Self {
        Self {
            cb_size: size_of::<Self>() as u32,
            hwnd,
            callback_message: 0,
            edge: 0,
            rc: Rect::default(),
            l_param: 0,
        }
    }
}

/// `POINT`.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct Point {
    /// Horizontal coordinate.
    pub x: i32,
    /// Vertical coordinate.
    pub y: i32,
}

/// `MSG`.
///
/// `l_private` is declared by `winuser.h` only under `_MAC`; on x64 it sits in
/// what is otherwise the structure's tail padding, so the struct is 48 bytes
/// either way. Declaring it is free, and reading a message into a buffer the
/// system considers larger than ours is the failure that is not free.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default)]
pub struct Msg {
    /// Window the message is for, or null for a thread message.
    pub hwnd: Handle,
    /// `WM_*`.
    pub message: u32,
    /// First parameter.
    pub w_param: Wparam,
    /// Second parameter.
    pub l_param: Lparam,
    /// `GetTickCount` milliseconds when the message was posted — the clock
    /// [`TimeBase`](super::TimeBase) rebases.
    pub time: u32,
    /// Cursor position in screen coordinates when the message was posted.
    pub pt: Point,
    /// Undocumented tail; see the type docs.
    pub l_private: u32,
}

// The derived `Default` zeroes every field, including the `Handle`, which is
// what `PeekMessageW` expects to be handed: it writes the whole structure and
// reads none of it.

/// `WNDCLASSEXW`.
#[repr(C)]
#[derive(Clone, Copy, Debug)]
pub struct WndClassExW {
    /// `size_of::<WndClassExW>()`, which the system validates.
    pub cb_size: u32,
    /// `CS_*` class styles.
    pub style: u32,
    /// The window procedure.
    pub lpfn_wnd_proc: WindowProc,
    /// Extra bytes after the class structure. Zero.
    pub cb_cls_extra: i32,
    /// Extra bytes after each window instance. Zero — this backend keeps its
    /// per-window state in `GWLP_USERDATA` instead; see [`super::proc`].
    pub cb_wnd_extra: i32,
    /// Module that owns the class.
    pub h_instance: Handle,
    /// Large icon. Null: the default is used.
    pub h_icon: Handle,
    /// Class cursor.
    pub h_cursor: Handle,
    /// Background brush.
    pub hbr_background: Handle,
    /// Menu resource name. Null.
    pub lpsz_menu_name: *const u16,
    /// Class name, NUL-terminated UTF-16.
    pub lpsz_class_name: *const u16,
    /// Small icon. Null.
    pub h_icon_sm: Handle,
}

/// `CREATESTRUCTW`, of which this backend reads exactly one field.
///
/// [`lp_create_params`](Self::lp_create_params) is how the `lpParam` handed to
/// `CreateWindowExW` reaches the window procedure, and it is the only way:
/// `WM_NCCREATE` arrives before `CreateWindowExW` has returned, so there is no
/// `HWND` to have stored anything against yet.
#[repr(C)]
#[derive(Clone, Copy, Debug)]
pub struct CreateStructW {
    /// The `lpParam` argument of `CreateWindowExW`.
    pub lp_create_params: *mut c_void,
    /// Module handle.
    pub h_instance: Handle,
    /// Menu handle.
    pub h_menu: Handle,
    /// Parent window.
    pub hwnd_parent: Handle,
    /// Height.
    pub cy: i32,
    /// Width.
    pub cx: i32,
    /// Top.
    pub y: i32,
    /// Left.
    pub x: i32,
    /// Window style.
    pub style: i32,
    /// Window name.
    pub lpsz_name: *const u16,
    /// Class name.
    pub lpsz_class: *const u16,
    /// Extended style.
    pub dw_ex_style: u32,
}

/// `MINMAXINFO` — what `WM_GETMINMAXINFO` asks the window to fill in.
///
/// The two fields that matter are the **track** sizes, which bound an
/// interactive resize. `pt_max_size` bounds a *maximize* and is deliberately
/// left alone: a maximized window that is smaller than the monitor because a
/// size constraint said so is not what a maximize button means.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default)]
pub struct MinMaxInfo {
    /// Reserved.
    pub pt_reserved: Point,
    /// Size of a maximized window.
    pub pt_max_size: Point,
    /// Position of a maximized window.
    pub pt_max_position: Point,
    /// Smallest the user may drag the window to, in **window** pixels.
    pub pt_min_track_size: Point,
    /// Largest the user may drag the window to, in **window** pixels.
    pub pt_max_track_size: Point,
}

/// `WINDOWPLACEMENT` — the whole of a window's restored geometry and show
/// state.
///
/// Saved on the way into borderless and restored on the way out, because
/// remembering only the window rectangle loses whether the window was
/// maximized, and restoring a maximized window as a floating one of the same
/// size is visibly wrong.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default)]
pub struct WindowPlacement {
    /// `size_of::<WindowPlacement>()`, which the system validates.
    pub length: u32,
    /// `WPF_*` flags.
    pub flags: u32,
    /// `SW_*` show state.
    pub show_cmd: u32,
    /// Minimized position.
    pub pt_min_position: Point,
    /// Maximized position.
    pub pt_max_position: Point,
    /// Restored rectangle, in workspace coordinates.
    pub rc_normal_position: Rect,
}

/// `MONITORINFOEXW`.
///
/// The `EX` half is [`sz_device`](Self::sz_device), and it is why this is the
/// structure used rather than plain `MONITORINFO`: the device name is the only
/// stable per-monitor identity Win32 offers without a second API, and
/// [`MonitorId`](crate::MonitorId) must not be reused within a session.
#[repr(C)]
#[derive(Clone, Copy, Debug)]
pub struct MonitorInfoExW {
    /// `size_of::<MonitorInfoExW>()`, which selects the `EX` form.
    pub cb_size: u32,
    /// The monitor's rectangle in virtual-screen coordinates.
    pub rc_monitor: Rect,
    /// The same, minus taskbars and appbars.
    pub rc_work: Rect,
    /// `MONITORINFOF_PRIMARY`.
    pub dw_flags: u32,
    /// `\\.\DISPLAY1` and friends, NUL-padded.
    pub sz_device: [u16; 32],
}

impl Default for MonitorInfoExW {
    fn default() -> Self {
        Self {
            cb_size: size_of::<Self>() as u32,
            rc_monitor: Rect::default(),
            rc_work: Rect::default(),
            dw_flags: 0,
            sz_device: [0; 32],
        }
    }
}

/// `DEVMODEW`, flattened.
///
/// The two unions in the real structure are each replaced by their display
/// arm, because this backend reads exactly one field out of it —
/// [`dm_display_frequency`](Self::dm_display_frequency) — and an arm only a
/// printer driver writes is layout, not meaning. The layout assertions in this
/// module's tests are what make that safe: get the padding wrong and every
/// field after the mistake is read from the wrong offset, which produces a
/// plausible number rather than a crash.
#[repr(C)]
#[derive(Clone, Copy, Debug)]
pub struct DevModeW {
    /// Device name.
    pub dm_device_name: [u16; 32],
    /// Structure version.
    pub dm_spec_version: u16,
    /// Driver version.
    pub dm_driver_version: u16,
    /// `size_of::<DevModeW>()`, which the driver validates.
    pub dm_size: u16,
    /// Extra driver bytes after this structure. Zero.
    pub dm_driver_extra: u16,
    /// Which fields are meaningful.
    pub dm_fields: u32,
    /// Where the display sits on the virtual desktop: `dmPosition`, the start
    /// of the printer/display union's display arm. The printer arm,
    /// `dmOrientation` to `dmPrintQuality`, covers the same bytes as this
    /// field and the two after it.
    pub dm_position: Point,
    /// `DMDO_*` rotation.
    pub dm_display_orientation: u32,
    /// `DMDFO_*` scaling, for a fixed-resolution output.
    pub dm_display_fixed_output: u32,
    /// Colour.
    pub dm_color: i16,
    /// Duplex.
    pub dm_duplex: i16,
    /// Y resolution.
    pub dm_y_resolution: i16,
    /// TrueType option.
    pub dm_tt_option: i16,
    /// Collation.
    pub dm_collate: i16,
    /// Form name.
    pub dm_form_name: [u16; 32],
    /// Logical pixels per inch.
    pub dm_log_pixels: u16,
    /// Bits per pixel.
    pub dm_bits_per_pel: u32,
    /// Width in pixels.
    pub dm_pels_width: u32,
    /// Height in pixels.
    pub dm_pels_height: u32,
    /// The display-flags/n-up union, both of whose arms are a `DWORD`.
    pub dm_display_flags: u32,
    /// **Refresh rate in whole hertz.** The only field this backend reads.
    pub dm_display_frequency: u32,
    /// ICM method.
    pub dm_icm_method: u32,
    /// ICM intent.
    pub dm_icm_intent: u32,
    /// Media type.
    pub dm_media_type: u32,
    /// Dither type.
    pub dm_dither_type: u32,
    /// Reserved.
    pub dm_reserved1: u32,
    /// Reserved.
    pub dm_reserved2: u32,
    /// Panning width.
    pub dm_panning_width: u32,
    /// Panning height.
    pub dm_panning_height: u32,
}

impl Default for DevModeW {
    fn default() -> Self {
        // Zeroed apart from `dm_size`, which is how the driver knows which
        // fields of which generation of the structure it may write.
        Self {
            dm_device_name: [0; 32],
            dm_spec_version: 0,
            dm_driver_version: 0,
            dm_size: size_of::<Self>() as u16,
            dm_driver_extra: 0,
            dm_fields: 0,
            dm_position: Point::default(),
            dm_display_orientation: 0,
            dm_display_fixed_output: 0,
            dm_color: 0,
            dm_duplex: 0,
            dm_y_resolution: 0,
            dm_tt_option: 0,
            dm_collate: 0,
            dm_form_name: [0; 32],
            dm_log_pixels: 0,
            dm_bits_per_pel: 0,
            dm_pels_width: 0,
            dm_pels_height: 0,
            dm_display_flags: 0,
            dm_display_frequency: 0,
            dm_icm_method: 0,
            dm_icm_intent: 0,
            dm_media_type: 0,
            dm_dither_type: 0,
            dm_reserved1: 0,
            dm_reserved2: 0,
            dm_panning_width: 0,
            dm_panning_height: 0,
        }
    }
}

/// `LUID` — a locally unique identifier; here, which adapter (GPU) a
/// `QueryDisplayConfig` path or mode belongs to.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct Luid {
    /// Low 32 bits.
    pub low_part: u32,
    /// High 32 bits.
    pub high_part: i32,
}

/// `DISPLAYCONFIG_2DREGION` — a width and height, with no position.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct DisplayConfig2dRegion {
    /// Width in pixels.
    pub cx: u32,
    /// Height in pixels.
    pub cy: u32,
}

/// `DISPLAYCONFIG_RATIONAL` — a numerator over a denominator, the exact form
/// `QueryDisplayConfig` reports a signal rate in.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct DisplayConfigRational {
    /// Numerator.
    pub numerator: u32,
    /// Denominator.
    pub denominator: u32,
}

impl DisplayConfigRational {
    /// The rate this rational expresses in millihertz, truncated, or `None`
    /// for a degenerate rational (a zero numerator or denominator).
    ///
    /// `divider` is the signal's `vSyncFreqDivider` (0 for a progressive
    /// mode): when non-zero, the rate is the rational divided by it, which is
    /// the interlaced case. 60000/1001 → 59940, the 59.94 Hz mode
    /// `EnumDisplaySettingsW` reports as the integer 60.
    pub const fn millihertz(self, divider: u32) -> Option<u32> {
        if self.numerator == 0 || self.denominator == 0 {
            return None;
        }
        let denominator = if divider == 0 {
            self.denominator
        } else {
            self.denominator.saturating_mul(divider)
        };
        if denominator == 0 {
            return None;
        }
        Some(self.numerator.saturating_mul(1_000) / denominator)
    }
}

/// `DISPLAYCONFIG_VIDEO_SIGNAL_INFO` — the signal a target mode describes.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct DisplayConfigVideoSignalInfo {
    /// Pixel clock in hertz.
    pub pixel_rate: u64,
    /// Horizontal sync frequency.
    pub h_sync_freq: DisplayConfigRational,
    /// Vertical sync frequency — the refresh rate, once
    /// [`additional_signal_info`](Self::additional_signal_info)'s divider has
    /// been applied.
    pub v_sync_freq: DisplayConfigRational,
    /// The visible region.
    pub active_size: DisplayConfig2dRegion,
    /// The whole scan-out region.
    pub total_size: DisplayConfig2dRegion,
    /// The `AdditionalSignalInfo` union value: `videoStandard` in the low 16
    /// bits, `vSyncFreqDivider` in bits 16-21.
    pub additional_signal_info: u32,
    /// `DISPLAYCONFIG_SCANLINE_ORDERING`.
    pub scan_line_ordering: i32,
}

/// `DISPLAYCONFIG_TARGET_MODE` — the mode a target (a display) is driving.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct DisplayConfigTargetMode {
    /// The signal, including the exact refresh rational.
    pub target_video_signal_info: DisplayConfigVideoSignalInfo,
}

/// `DISPLAYCONFIG_MODE_INFO` — one entry of the mode array `QueryDisplayConfig`
/// fills.
///
/// The tail is a union of a 48-byte `DISPLAYCONFIG_TARGET_MODE` and a 20-byte
/// `DISPLAYCONFIG_SOURCE_MODE`, so [`target_mode`](Self::target_mode) — the
/// larger arm — determines the layout. This backend only reads target modes.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct DisplayConfigModeInfo {
    /// `DISPLAYCONFIG_MODE_INFO_TYPE`: target, source or desktop image.
    pub info_type: i32,
    /// The adapter's id for this mode.
    pub id: u32,
    /// The adapter this mode belongs to.
    pub adapter_id: Luid,
    /// The union's larger arm, and therefore the layout; valid only when
    /// `info_type` is `DISPLAYCONFIG_MODE_INFO_TYPE_TARGET`.
    pub target_mode: DisplayConfigTargetMode,
}

/// `DISPLAYCONFIG_PATH_SOURCE_INFO` — the source half of a path.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct DisplayConfigPathSourceInfo {
    /// The adapter.
    pub adapter_id: Luid,
    /// The source's id on that adapter.
    pub id: u32,
    /// The `modeInfoIdx` union value: the **source** mode's index in the high
    /// 16 bits, the clone-group id in the low 16.
    pub mode_info_idx: u32,
    /// `DISPLAYCONFIG_SOURCE_IN_USE` and friends.
    pub status_flags: u32,
}

/// `DISPLAYCONFIG_PATH_TARGET_INFO` — the target half of a path.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct DisplayConfigPathTargetInfo {
    /// The adapter.
    pub adapter_id: Luid,
    /// The target's id on that adapter.
    pub id: u32,
    /// The `modeInfoIdx` union value: the **target** mode's index in the high
    /// 16 bits, the desktop-mode index in the low 16.
    pub mode_info_idx: u32,
    /// `DISPLAYCONFIG_VIDEO_OUTPUT_TECHNOLOGY`.
    pub output_technology: i32,
    /// `DISPLAYCONFIG_ROTATION`.
    pub rotation: i32,
    /// `DISPLAYCONFIG_SCALING`.
    pub scaling: i32,
    /// The path's own refresh; the target mode's signal carries the exact one.
    pub refresh_rate: DisplayConfigRational,
    /// `DISPLAYCONFIG_SCANLINE_ORDERING`.
    pub scan_line_ordering: i32,
    /// Whether the target is present.
    pub target_available: Bool32,
    /// `DISPLAYCONFIG_TARGET_IN_USE` and friends.
    pub status_flags: u32,
}

impl DisplayConfigPathTargetInfo {
    /// The target mode's index in the mode array `QueryDisplayConfig` filled:
    /// the high 16 bits of [`mode_info_idx`](Self::mode_info_idx), whose low 16
    /// bits are the desktop-mode index and are ignored. `None` for the "no
    /// mode" sentinel, `DISPLAYCONFIG_PATH_TARGET_MODE_IDX_INVALID`.
    pub const fn target_mode_index(self) -> Option<usize> {
        let index = (self.mode_info_idx >> 16) as usize;
        if index == value::DISPLAYCONFIG_PATH_TARGET_MODE_IDX_INVALID as usize {
            None
        } else {
            Some(index)
        }
    }
}

/// `DISPLAYCONFIG_PATH_INFO` — one path: a source driving a target.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct DisplayConfigPathInfo {
    /// The source half.
    pub source_info: DisplayConfigPathSourceInfo,
    /// The target half.
    pub target_info: DisplayConfigPathTargetInfo,
    /// `DISPLAYCONFIG_PATH_ACTIVE` and friends.
    pub flags: u32,
}

/// `DISPLAYCONFIG_DEVICE_INFO_HEADER` — the request every
/// `DisplayConfigGetDeviceInfo` call is framed with.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct DisplayConfigDeviceInfoHeader {
    /// `DISPLAYCONFIG_DEVICE_INFO_TYPE`: which request this is.
    pub kind: i32,
    /// Size of the request structure, which the system validates.
    pub size: u32,
    /// The adapter the request is about.
    pub adapter_id: Luid,
    /// The source or target id on that adapter.
    pub id: u32,
}

/// `DISPLAYCONFIG_SOURCE_DEVICE_NAME` — the `GET_SOURCE_NAME` request's answer.
///
/// [`view_gdi_device_name`](Self::view_gdi_device_name) is the source's
/// `\\.\DISPLAYn` name — the same string `MONITORINFOEXW::szDevice` carries,
/// which is the identity this backend maps monitors through.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct DisplayConfigSourceDeviceName {
    /// The request header, answered in place.
    pub header: DisplayConfigDeviceInfoHeader,
    /// The GDI device name, NUL-padded. `CCHDEVICENAME` = 32.
    pub view_gdi_device_name: [u16; 32],
}

/// `TRACKMOUSEEVENT` — what `TrackMouseEvent` is asked to watch for.
///
/// Needed because **Windows has no `WM_MOUSEENTER`**. A window is told when the
/// pointer leaves and never when it arrives, and only if it asked: this
/// structure is the asking, and it re-arms one shot at a time. See
/// [`proc`](super::proc) for where the entry half is derived from.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default)]
pub struct TrackMouse {
    /// `size_of::<TrackMouse>()`, which the system validates.
    pub cb_size: u32,
    /// `TME_*`.
    pub dw_flags: u32,
    /// The window to watch.
    pub hwnd_track: Handle,
    /// Hover timeout, unused without `TME_HOVER`.
    pub dw_hover_time: u32,
}

/// `DROPFILES` — the header of the block an `HDROP` names.
///
/// **Test-only, and deliberately.** The backend never parses this: it reads a
/// drop through `DragQueryFileW`, which is shell32's job precisely because the
/// [`f_wide`](Self::f_wide) ANSI case and the file list's framing are shell32's
/// to own. What a test needs is the other direction — CI has nobody to drag a
/// file onto a window, so the only way to exercise `WM_DROPFILES` at all is to
/// build the block the shell would have handed over and send the message.
///
/// The layout assertion in this module's tests is what makes that synthesis
/// trustworthy: a header of the wrong length puts the file list at an offset
/// `DragQueryFileW` does not look at, and the test would then report zero files
/// and read as a backend bug.
///
/// `shlobj_core.h` declares it under `pshpack1.h`, so the C structure is
/// byte-aligned; this one is 4-aligned with the same size and offsets. That is
/// only safe in the direction it is used — a test writing a block for shell32
/// to read — and would not be for reading a `DROPFILES` out of shell memory.
#[cfg(test)]
#[repr(C)]
#[derive(Clone, Copy, Debug, Default)]
pub struct DropFiles {
    /// Offset of the file list from the start of this structure, in bytes.
    pub p_files: u32,
    /// Where the drop happened, in the window's client coordinates.
    pub pt: Point,
    /// Whether the drop was on the non-client area.
    pub f_nc: Bool32,
    /// **`TRUE` for a `WCHAR` file list**, which is the only kind this engine
    /// produces and the field an ANSI-era sender sets to `FALSE`.
    pub f_wide: Bool32,
}

/// `RAWINPUTDEVICE` — one usage page/usage pair to receive `WM_INPUT` for.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default)]
pub struct RawInputDevice {
    /// HID usage page. `0x01` is the generic desktop page.
    pub us_usage_page: u16,
    /// HID usage within the page. `0x02` is the mouse.
    pub us_usage: u16,
    /// `RIDEV_*`.
    pub dw_flags: u32,
    /// Where `WM_INPUT` is delivered. Null means "follow the keyboard focus",
    /// which is what this backend wants — see [`input`](super::input).
    pub hwnd_target: Handle,
}

/// `RAWINPUTHEADER`.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default)]
pub struct RawInputHeader {
    /// `RIM_TYPE*`.
    pub dw_type: u32,
    /// Size of the whole `RAWINPUT` this heads.
    pub dw_size: u32,
    /// The device that produced it, or null for injected input. What a
    /// [`DeviceId`](crcbl_core::input::DeviceId) is resolved from; see
    /// [`devices`](super::devices).
    pub h_device: Handle,
    /// The `wParam` of the `WM_INPUT` that carried it.
    pub w_param: Wparam,
}

/// `RAWMOUSE`.
///
/// The two-byte hole after [`us_flags`](Self::us_flags) is the C union's
/// alignment, spelled out rather than left to the compiler: the union's first
/// arm is a `ULONG`, so it starts at offset 4 whatever `usFlags` did. Naming it
/// changes nothing the compiler would not have done — `#[repr(C)]` inserts the
/// same two bytes — and it is here so a reader diffing this against `winuser.h`
/// can see that the gap was noticed rather than missed.
///
/// The layout assertion in this module's tests checks every field's offset and
/// width, so a field that is absent, the wrong width or swapped with its
/// neighbour all fail it. That is the real hazard: reading
/// [`l_last_x`](Self::l_last_x) from offset 8 instead of 12 gives half a button
/// mask as a mouse delta, and a plausible number rather than a crash. Same
/// shape as [`DevModeW`]'s, checked the same way.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default)]
pub struct RawMouse {
    /// `MOUSE_MOVE_RELATIVE`, `MOUSE_MOVE_ABSOLUTE`, `MOUSE_VIRTUAL_DESKTOP`.
    /// **The field that decides what the two coordinates mean.**
    pub us_flags: u16,
    /// The union's alignment padding.
    pub padding: u16,
    /// `usButtonFlags` in the low half — the `RI_MOUSE_*` edges this report
    /// carries — and `usButtonData`, the wheel delta, in the high half. Not
    /// turned into events: the button *messages* carry position and ordering,
    /// and raw edges would double every click. Read only to say which device a
    /// button message came from.
    pub ul_buttons: u32,
    /// Raw button state, likewise unread.
    pub ul_raw_buttons: u32,
    /// Relative motion, or an absolute coordinate — see
    /// [`us_flags`](Self::us_flags).
    pub l_last_x: i32,
    /// See [`l_last_x`](Self::l_last_x).
    pub l_last_y: i32,
    /// Driver-supplied extra information.
    pub ul_extra_information: u32,
}

/// `COMPOSITIONFORM` — where an input method draws its composition window.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default)]
pub struct CompositionForm {
    /// `CFS_*`: which of the two fields below mean anything.
    pub dw_style: u32,
    /// The window's top-left, in client coordinates, for `CFS_POINT`.
    pub pt_current_pos: Point,
    /// The area it may use, in client coordinates, for `CFS_RECT` (not used
    /// here: `CFS_POINT` puts the window at the caret).
    pub rc_area: Rect,
}

/// `CANDIDATEFORM` — where an input method opens its candidate list.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default)]
pub struct CandidateForm {
    /// Which candidate list; `0` is the one every input method has.
    pub dw_index: u32,
    /// `CFS_*`.
    pub dw_style: u32,
    /// Where the list goes, in client coordinates.
    pub pt_current_pos: Point,
    /// For `CFS_EXCLUDE`, the area the list must not cover.
    pub rc_area: Rect,
}

/// `RAWKEYBOARD`.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default)]
pub struct RawKeyboard {
    /// The set 1 scan code, without its prefix — see
    /// [`flags`](Self::flags).
    pub make_code: u16,
    /// `RI_KEY_BREAK` for a release, `RI_KEY_E0`/`RI_KEY_E1` for a prefix.
    pub flags: u16,
    /// Reserved.
    pub reserved: u16,
    /// The virtual key. Not read: the key *message* is what names the symbol.
    pub v_key: u16,
    /// The legacy message this report corresponds to.
    pub message: u32,
    /// Driver-supplied extra information.
    pub extra_information: u32,
}

/// The tail of `RAWINPUT`, narrowed to the two arms this backend registers.
///
/// `RAWHID` is the third arm and variable-length; no HID usage other than the
/// generic mouse and keyboard is registered, so it cannot arrive.
#[repr(C)]
#[derive(Clone, Copy)]
pub union RawInputData {
    /// Valid when the header's `dwType` is `RIM_TYPEMOUSE`.
    pub mouse: RawMouse,
    /// Valid when the header's `dwType` is `RIM_TYPEKEYBOARD`.
    pub keyboard: RawKeyboard,
}

/// `RAWINPUT`.
///
/// The [`header`](Self::header)'s `dwType` is checked before either arm of
/// [`data`](Self::data) is read, which is what makes the union sound rather than
/// hopeful. [`Default`] initializes the larger arm, so every byte of the smaller
/// one is initialized too.
#[repr(C)]
#[derive(Clone, Copy)]
pub struct RawInput {
    /// Type, size and source device.
    pub header: RawInputHeader,
    /// The report, as the header's type says.
    pub data: RawInputData,
}

impl Default for RawInput {
    fn default() -> Self {
        Self {
            header: RawInputHeader::default(),
            data: RawInputData {
                mouse: RawMouse::default(),
            },
        }
    }
}

// ---------------------------------------------------------------------------
// Constants
// ---------------------------------------------------------------------------

/// Window and extended window styles.
pub mod style {
    /// `WS_POPUP` — no frame, no caption. Borderless is this bit and the
    /// absence of the others.
    pub const POPUP: u32 = 0x8000_0000;
    /// `WS_VISIBLE`.
    pub const VISIBLE: u32 = 0x1000_0000;
    /// `WS_CLIPSIBLINGS`.
    pub const CLIP_SIBLINGS: u32 = 0x0400_0000;
    /// `WS_CLIPCHILDREN`.
    pub const CLIP_CHILDREN: u32 = 0x0200_0000;
    /// `WS_CAPTION` — the title bar, and `WS_BORDER | WS_DLGFRAME`.
    pub const CAPTION: u32 = 0x00C0_0000;
    /// `WS_SYSMENU` — the system menu, and therefore the close button.
    pub const SYS_MENU: u32 = 0x0008_0000;
    /// `WS_THICKFRAME` — the resize border.
    pub const THICK_FRAME: u32 = 0x0004_0000;
    /// `WS_MINIMIZEBOX`.
    pub const MINIMIZE_BOX: u32 = 0x0002_0000;
    /// `WS_MAXIMIZEBOX`.
    pub const MAXIMIZE_BOX: u32 = 0x0001_0000;
    /// `WS_OVERLAPPEDWINDOW`.
    pub const OVERLAPPED_WINDOW: u32 =
        CAPTION | SYS_MENU | THICK_FRAME | MINIMIZE_BOX | MAXIMIZE_BOX;

    /// `WS_EX_APPWINDOW` — force a taskbar button.
    pub const EX_APP_WINDOW: u32 = 0x0004_0000;
    /// `WS_EX_WINDOWEDGE`.
    pub const EX_WINDOW_EDGE: u32 = 0x0000_0100;
    /// `WS_EX_TOOLWINDOW` — no taskbar button and no place in Alt-Tab: what
    /// a panel is.
    pub const EX_TOOL_WINDOW: u32 = 0x0000_0080;
    /// `WS_EX_TOPMOST` — above every window without it.
    pub const EX_TOPMOST: u32 = 0x0000_0008;
    /// `WS_EX_NOACTIVATE` — a click does not make the window the foreground
    /// one, so the keyboard stays where it was. Mouse messages still arrive.
    pub const EX_NO_ACTIVATE: u32 = 0x0800_0000;
    /// `WS_EX_NOREDIRECTIONBITMAP` — DWM keeps no redirection surface for the
    /// window, so it shows only what DirectComposition gives it: what a
    /// transparent window is. Fixed at creation; a style rewrite carries it
    /// across rather than trying to change it.
    pub const EX_NO_REDIRECTION_BITMAP: u32 = 0x0020_0000;
    /// `WS_EX_ACCEPTFILES` — **what `DragAcceptFiles` sets**, and therefore
    /// state rather than style.
    ///
    /// Documented as the extended style that call toggles, which is the whole
    /// reason it is named here: a mode change rewrites the extended style word
    /// from [`geometry::styles`](super::super::geometry::styles), and a rewrite
    /// that does not carry this bit across silently stops a window receiving
    /// `WM_DROPFILES`. Exactly the hazard `WS_VISIBLE` has, one word over.
    pub const EX_ACCEPT_FILES: u32 = 0x0000_0010;
}

/// `DwmSetWindowAttribute`'s attributes and values, for the frame a
/// transparent window is given.
pub mod dwm {
    /// `DWMWA_WINDOW_CORNER_PREFERENCE`: whether DWM rounds the window's
    /// corners. Windows 11 and later; earlier versions refuse the attribute and
    /// never round.
    pub const WINDOW_CORNER_PREFERENCE: u32 = 33;
    /// `DWMWCP_DEFAULT`: the system decides.
    pub const CORNER_DEFAULT: u32 = 0;
    /// `DWMWCP_DONOTROUND`: square corners.
    pub const CORNER_DO_NOT_ROUND: u32 = 1;
    /// `DWMWA_BORDER_COLOR`: the colour of the border DWM draws around the
    /// window. Windows 11 and later, like the corner preference.
    pub const BORDER_COLOR: u32 = 34;
    /// `DWMWA_COLOR_DEFAULT`: the system's border.
    pub const COLOR_DEFAULT: u32 = 0xFFFF_FFFF;
    /// `DWMWA_COLOR_NONE`: no border at all.
    pub const COLOR_NONE: u32 = 0xFFFF_FFFE;
}

/// `SHAppBarMessage`'s messages, edges and notifications.
pub mod appbar {
    /// `ABM_NEW`: registers an appbar and its callback message.
    pub const NEW: u32 = 0x0000_0000;
    /// `ABM_REMOVE`: gives the appbar's space back.
    pub const REMOVE: u32 = 0x0000_0001;
    /// `ABM_QUERYPOS`: asks where a proposed rectangle may go, which moves it
    /// clear of the taskbar and every other appbar on that edge.
    pub const QUERY_POS: u32 = 0x0000_0002;
    /// `ABM_SETPOS`: reserves the rectangle.
    pub const SET_POS: u32 = 0x0000_0003;
    /// `ABM_ACTIVATE`: the appbar was activated or deactivated.
    pub const ACTIVATE: u32 = 0x0000_0006;
    /// `ABM_WINDOWPOSCHANGED`: the appbar's window moved.
    pub const WINDOW_POS_CHANGED: u32 = 0x0000_0009;

    /// `ABE_LEFT`.
    pub const EDGE_LEFT: u32 = 0;
    /// `ABE_TOP`.
    pub const EDGE_TOP: u32 = 1;
    /// `ABE_RIGHT`.
    pub const EDGE_RIGHT: u32 = 2;
    /// `ABE_BOTTOM`.
    pub const EDGE_BOTTOM: u32 = 3;

    /// `ABN_POSCHANGED`: the taskbar or another appbar moved, so this one has
    /// to ask for its place again.
    pub const POS_CHANGED: u32 = 0x0000_0001;
    /// `ABN_FULLSCREENAPP`: a full-screen window opened on this appbar's
    /// monitor (`lParam` nonzero) or the last one closed (zero).
    pub const FULL_SCREEN_APP: u32 = 0x0000_0002;
}

/// The messages the window procedure recognizes.
pub mod msg {
    /// `WM_DESTROY`.
    pub const DESTROY: u32 = 0x0002;
    /// `WM_MOVE` — the window moved, so a pointer clip built from its client
    /// rectangle is now in the wrong place.
    pub const MOVE: u32 = 0x0003;
    /// `WM_SIZE`.
    pub const SIZE: u32 = 0x0005;
    /// `WM_ACTIVATE` — a window of this thread was activated or deactivated.
    pub const ACTIVATE: u32 = 0x0006;
    /// `WM_SETFOCUS`.
    pub const SET_FOCUS: u32 = 0x0007;
    /// `WM_KILLFOCUS`.
    pub const KILL_FOCUS: u32 = 0x0008;
    /// `WM_CLOSE`.
    pub const CLOSE: u32 = 0x0010;
    /// `WM_ACTIVATEAPP` — the foreground moved to or from another process.
    pub const ACTIVATE_APP: u32 = 0x001C;
    /// `WM_SETCURSOR` — asked on every pointer movement over the window, and
    /// the **only** place a cursor shape may be set.
    pub const SET_CURSOR: u32 = 0x0020;
    /// `WM_NCHITTEST` — which part of the window a point is over, and whether
    /// the window is there at all for the pointer.
    pub const NC_HIT_TEST: u32 = 0x0084;
    /// `WM_GETMINMAXINFO`.
    pub const GET_MIN_MAX_INFO: u32 = 0x0024;
    /// `WM_GETOBJECT` — an accessibility client asking for the window's
    /// provider. `lParam` names which object; see `access`. Behind the
    /// feature, because without an adapter nothing answers it.
    #[cfg(feature = "accesskit")]
    pub const GET_OBJECT: u32 = 0x003D;
    /// `WM_DISPLAYCHANGE`.
    pub const DISPLAY_CHANGE: u32 = 0x007E;
    /// `WM_WINDOWPOSCHANGED` — the window's size, position or place in the
    /// z-order changed. The default handler is what sends `WM_SIZE` and
    /// `WM_MOVE` from it.
    pub const WINDOW_POS_CHANGED: u32 = 0x0047;
    /// `WM_SETTINGCHANGE` — a system parameter changed. With
    /// [`SPI_SET_WORK_AREA`](super::value::SPI_SET_WORK_AREA) it is a monitor's
    /// work area moving: the taskbar, or an appbar coming or going.
    pub const SETTING_CHANGE: u32 = 0x001A;
    /// `WM_APP + 1`: what this backend registers appbars with, so the shell's
    /// `ABN_*` notifications arrive as this message, with the notification in
    /// `wParam`.
    pub const APP_BAR: u32 = 0x8001;
    /// `WM_NCCREATE`.
    pub const NC_CREATE: u32 = 0x0081;
    /// `WM_NCDESTROY`.
    pub const NC_DESTROY: u32 = 0x0082;
    /// `WM_INPUT_DEVICE_CHANGE` — a raw input device arrived or left. `lParam`
    /// is its handle, `wParam` says which.
    pub const INPUT_DEVICE_CHANGE: u32 = 0x00FE;
    /// `WM_INPUT` — a raw input report.
    pub const INPUT: u32 = 0x00FF;
    /// `WM_KEYDOWN`.
    pub const KEY_DOWN: u32 = 0x0100;
    /// `WM_KEYUP`.
    pub const KEY_UP: u32 = 0x0101;
    /// `WM_CHAR` — one UTF-16 code unit of committed text.
    pub const CHAR: u32 = 0x0102;
    /// `WM_SYSKEYDOWN` — a key pressed with Alt held, or F10.
    pub const SYS_KEY_DOWN: u32 = 0x0104;
    /// `WM_SYSKEYUP`.
    pub const SYS_KEY_UP: u32 = 0x0105;
    /// `WM_IME_STARTCOMPOSITION` — an input method began composing.
    pub const IME_START_COMPOSITION: u32 = 0x010D;
    /// `WM_IME_ENDCOMPOSITION` — the composition was committed or abandoned.
    pub const IME_END_COMPOSITION: u32 = 0x010E;
    /// `WM_IME_COMPOSITION` — the composition changed. `lParam` holds the
    /// `GCS_*` flags naming what did.
    pub const IME_COMPOSITION: u32 = 0x010F;
    /// `WM_IME_SETCONTEXT` — the window is gaining or losing the active input
    /// context. `lParam` holds the `ISC_*` flags saying which of the input
    /// method's own windows the default handler should show.
    pub const IME_SET_CONTEXT: u32 = 0x0281;
    /// `WM_SYSCOMMAND` — a window-menu command. `wParam`'s low four bits are
    /// the system's own and are masked off before comparing with an `SC_*`.
    pub const SYS_COMMAND: u32 = 0x0112;
    /// `WM_MOUSEMOVE`.
    pub const MOUSE_MOVE: u32 = 0x0200;
    /// `WM_LBUTTONDOWN`.
    pub const L_BUTTON_DOWN: u32 = 0x0201;
    /// `WM_LBUTTONUP`.
    pub const L_BUTTON_UP: u32 = 0x0202;
    /// `WM_RBUTTONDOWN`.
    pub const R_BUTTON_DOWN: u32 = 0x0204;
    /// `WM_RBUTTONUP`.
    pub const R_BUTTON_UP: u32 = 0x0205;
    /// `WM_MBUTTONDOWN`.
    pub const M_BUTTON_DOWN: u32 = 0x0207;
    /// `WM_MBUTTONUP`.
    pub const M_BUTTON_UP: u32 = 0x0208;
    /// `WM_MOUSEWHEEL`.
    pub const MOUSE_WHEEL: u32 = 0x020A;
    /// `WM_XBUTTONDOWN` — the two thumb buttons, told apart by `wParam`.
    pub const X_BUTTON_DOWN: u32 = 0x020B;
    /// `WM_XBUTTONUP`.
    pub const X_BUTTON_UP: u32 = 0x020C;
    /// `WM_MOUSEHWHEEL` — the tilt wheel.
    pub const MOUSE_H_WHEEL: u32 = 0x020E;
    /// `WM_POINTERUPDATE` — a pointer moved or changed state. `wParam`'s low
    /// word is the pointer id and its high word the `POINTER_MESSAGE_FLAG_*`
    /// bits; `lParam` is the position in **screen** coordinates.
    pub const POINTER_UPDATE: u32 = 0x0245;
    /// `WM_POINTERDOWN` — a pointer made contact.
    pub const POINTER_DOWN: u32 = 0x0246;
    /// `WM_POINTERUP` — a pointer broke contact.
    pub const POINTER_UP: u32 = 0x0247;
    /// `WM_POINTERCAPTURECHANGED` — the window lost the pointer's capture, so
    /// the rest of its gesture will not arrive here.
    pub const POINTER_CAPTURE_CHANGED: u32 = 0x024C;
    /// `WM_SIZING`.
    pub const SIZING: u32 = 0x0214;
    /// `WM_CAPTURECHANGED` — somebody else took the mouse capture, so ours is
    /// gone whether we released it or not.
    pub const CAPTURE_CHANGED: u32 = 0x0215;
    /// `WM_DROPFILES` — files were dropped on a window that asked for them with
    /// `DragAcceptFiles`. `wParam` is an `HDROP`; see [`dnd`](super::super::dnd).
    pub const DROP_FILES: u32 = 0x0233;
    /// `WM_EXITSIZEMOVE` — the modal drag loop finished.
    pub const EXIT_SIZE_MOVE: u32 = 0x0232;
    /// `WM_MOUSELEAVE` — the one-shot `TrackMouseEvent` armed for.
    pub const MOUSE_LEAVE: u32 = 0x02A3;
    /// `WM_DPICHANGED`.
    pub const DPI_CHANGED: u32 = 0x02E0;
}

/// Everything else, by the name it has in the SDK.
pub mod value {
    /// `SIZE_MINIMIZED`, the `wParam` of a `WM_SIZE` that means "iconified".
    pub const SIZE_MINIMIZED: usize = 1;

    /// `GWL_STYLE`.
    pub const GWL_STYLE: i32 = -16;
    /// `GWL_EXSTYLE`.
    pub const GWL_EX_STYLE: i32 = -20;
    /// `GWLP_USERDATA` — where the window procedure finds this shell's shared
    /// state. See the `proc` module.
    pub const GWLP_USERDATA: i32 = -21;

    /// `SW_HIDE`.
    pub const SW_HIDE: i32 = 0;
    /// `SW_SHOWNORMAL`.
    pub const SW_SHOW_NORMAL: i32 = 1;
    /// `SW_SHOWNOACTIVATE` — shown at its last size and position, and not
    /// activated: how a panel that takes no keyboard is shown.
    pub const SW_SHOW_NO_ACTIVATE: i32 = 4;
    /// `SW_MINIMIZE`: `ShowWindow` command that iconifies the window.
    ///
    /// Test-only, like [`PM_NOREMOVE`]: the backend never minimizes a window,
    /// and the clip test restores it again with [`SW_RESTORE`].
    #[cfg(test)]
    pub const SW_MINIMIZE: i32 = 6;
    /// `SW_RESTORE`: `ShowWindow` command that un-iconifies and activates.
    ///
    /// Test-only; see [`SW_MINIMIZE`].
    #[cfg(test)]
    pub const SW_RESTORE: i32 = 9;

    /// `SWP_NOSIZE`.
    pub const SWP_NO_SIZE: u32 = 0x0001;
    /// `SWP_NOMOVE`.
    pub const SWP_NO_MOVE: u32 = 0x0002;
    /// `SWP_NOZORDER`.
    pub const SWP_NO_Z_ORDER: u32 = 0x0004;
    /// `SWP_NOACTIVATE`.
    pub const SWP_NO_ACTIVATE: u32 = 0x0010;
    /// `SWP_FRAMECHANGED` — **required** after a style change, or the system
    /// keeps drawing the old frame until something else forces a recalculation.
    pub const SWP_FRAME_CHANGED: u32 = 0x0020;
    /// `SWP_NOOWNERZORDER`.
    pub const SWP_NO_OWNER_Z_ORDER: u32 = 0x0200;
    /// `HWND_BOTTOM`, as `SetWindowPos`'s insert-after: the bottom of the
    /// z-order.
    pub const HWND_BOTTOM: isize = 1;
    /// `HWND_TOPMOST`, as `SetWindowPos`'s insert-after: the top of the
    /// topmost band, which the window joins.
    pub const HWND_TOPMOST: isize = -1;

    /// `PM_REMOVE`.
    pub const PM_REMOVE: u32 = 0x0001;

    /// `PM_NOREMOVE` — read the message at the head of the queue and leave it
    /// there.
    ///
    /// Test-only, and `#[cfg(test)]` rather than merely unused: the backend
    /// itself always drains with [`PM_REMOVE`], and the one caller is the
    /// diagnostic peek that explains a wait which came back before its timeout.
    /// A `QS_*` word says what *kind* of message is in the queue; this is how a
    /// test gets the id, the window and the parameters of the actual one.
    #[cfg(test)]
    pub const PM_NOREMOVE: u32 = 0x0000;

    /// `MONITORINFOF_PRIMARY`.
    pub const MONITOR_PRIMARY: u32 = 0x0000_0001;
    /// `MONITOR_DEFAULTTONEAREST`.
    pub const MONITOR_DEFAULT_TO_NEAREST: u32 = 0x0000_0002;

    /// `HTTRANSPARENT`, as `WM_NCHITTEST`'s answer: the window is not there
    /// for the pointer, which goes to the window beneath it on this thread.
    pub const HT_TRANSPARENT: isize = -1;

    /// `SPI_SETWORKAREA`, as `WM_SETTINGCHANGE`'s `wParam`.
    pub const SPI_SET_WORK_AREA: usize = 0x002F;

    /// `MDT_EFFECTIVE_DPI` — the scale the *user* chose, which is the one every
    /// other window on the desktop is laid out at.
    pub const MDT_EFFECTIVE_DPI: i32 = 0;

    /// `ENUM_CURRENT_SETTINGS`.
    pub const ENUM_CURRENT_SETTINGS: u32 = 0xFFFF_FFFF;

    /// `QDC_ONLY_ACTIVE_PATHS` — `QueryDisplayConfig` flags: only the paths
    /// currently driving a display.
    pub const QDC_ONLY_ACTIVE_PATHS: u32 = 0x0000_0002;
    /// `DISPLAYCONFIG_DEVICE_INFO_GET_SOURCE_NAME` — the
    /// `DisplayConfigGetDeviceInfo` request that names a path's source.
    pub const DISPLAYCONFIG_DEVICE_INFO_GET_SOURCE_NAME: i32 = 1;
    /// `DISPLAYCONFIG_MODE_INFO_TYPE_TARGET` — a mode array entry describing a
    /// target (a display) rather than a source.
    pub const DISPLAYCONFIG_MODE_INFO_TYPE_TARGET: i32 = 2;
    /// `DISPLAYCONFIG_PATH_TARGET_MODE_IDX_INVALID` — the "no mode" sentinel in
    /// the high 16 bits of `DisplayConfigPathTargetInfo::mode_info_idx`.
    pub const DISPLAYCONFIG_PATH_TARGET_MODE_IDX_INVALID: u32 = 0xffff;
    /// `ERROR_SUCCESS` — the LONG success code every `LONG`-returning call here
    /// reports.
    pub const ERROR_SUCCESS: i32 = 0;

    /// `DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2`, which is a pseudo-handle
    /// rather than an enumerator.
    pub const DPI_PER_MONITOR_AWARE_V2: isize = -4;

    /// `USER_DEFAULT_SCREEN_DPI` — the DPI that is 100%.
    pub const DEFAULT_DPI: u32 = 96;

    /// `CW_USEDEFAULT` — "you choose", for a position with no monitor to
    /// place against.
    ///
    /// The literal is `0x80000000` as a **signed** `int`, which is
    /// `i32::MIN` — not a large positive number, and a window placed at a
    /// large positive number is off the desktop.
    pub const CW_USE_DEFAULT: i32 = i32::MIN;

    /// `IDC_ARROW`, as the integer resource id `MAKEINTRESOURCE` wraps.
    pub const IDC_ARROW: usize = 32_512;
    /// `IDC_IBEAM`.
    pub const IDC_IBEAM: usize = 32_513;
    /// `IDC_WAIT`.
    pub const IDC_WAIT: usize = 32_514;
    /// `IDC_CROSS`.
    pub const IDC_CROSS: usize = 32_515;
    /// `IDC_SIZENWSE`.
    pub const IDC_SIZE_NWSE: usize = 32_642;
    /// `IDC_SIZENESW`.
    pub const IDC_SIZE_NESW: usize = 32_643;
    /// `IDC_SIZEWE`.
    pub const IDC_SIZE_WE: usize = 32_644;
    /// `IDC_SIZENS`.
    pub const IDC_SIZE_NS: usize = 32_645;
    /// `IDC_SIZEALL`.
    pub const IDC_SIZE_ALL: usize = 32_646;
    /// `IDC_NO`.
    pub const IDC_NO: usize = 32_648;
    /// `IDC_HAND`.
    pub const IDC_HAND: usize = 32_649;
    /// `IDC_APPSTARTING`.
    pub const IDC_APP_STARTING: usize = 32_650;

    /// `BLACK_BRUSH`.
    pub const BLACK_BRUSH: i32 = 4;
    /// `RGN_OR` — `CombineRgn` makes the union of its two sources.
    pub const RGN_OR: i32 = 2;
    /// `ERROR` — what `CombineRgn` answers when it could not combine.
    pub const REGION_ERROR: i32 = 0;
    /// `CS_HREDRAW | CS_VREDRAW` — repaint the whole client area on a resize,
    /// so a window being dragged wider does not show stale pixels in the strip
    /// that just appeared.
    pub const CS_REDRAW: u32 = 0x0002 | 0x0001;

    /// `ERROR_ACCESS_DENIED` — what `SetProcessDpiAwarenessContext`
    /// reports when the awareness was already set, by a manifest or by an
    /// earlier call.
    pub const ERROR_ACCESS_DENIED: u32 = 5;
    /// `ERROR_CLASS_ALREADY_EXISTS`.
    pub const ERROR_CLASS_ALREADY_EXISTS: u32 = 1410;

    /// `QS_ALLINPUT` — every kind of message, `QS_SENDMESSAGE` included.
    ///
    /// **Not what the wait asks for**; see [`QS_ALL_EVENTS`]. This is what
    /// `GetQueueStatus` is asked for when a test has to explain a wait that came
    /// back early, because reporting *everything* is what makes the diagnosis
    /// complete — and it is the bit this constant has and the other one does not
    /// that ended a three-round-trip investigation.
    ///
    /// `MWMO_INPUTAVAILABLE` is deliberately **not** declared beside it: the
    /// shell's `wait` drains the queue itself and then sleeps with no flags,
    /// which is the stronger form of what that flag was there for. The CI
    /// evidence that took it out is written up on that function.
    ///
    /// Test-only since the wait moved to [`QS_ALL_EVENTS`], on the same terms as
    /// [`Rect::intersect`](super::Rect::intersect): the backend never asks for
    /// this mask, and only a test has to *explain* a wake.
    #[cfg(test)]
    pub const QS_ALL_INPUT: u32 = 0x04FF;
    /// `QS_ALLEVENTS` — `QS_ALLINPUT` **minus `QS_SENDMESSAGE`**, and what
    /// [`wait`](crate::win32::Win32Shell) actually sleeps on.
    ///
    /// # The one bit that cannot be drained
    ///
    /// A message *sent* to a window of this thread — `SendMessageW` from another
    /// process, and the system does this constantly — sets `QS_SENDMESSAGE`.
    /// `PeekMessageW` **processes** such a message but never *returns* it, so it
    /// can neither report it nor clear its bit: the instrumented CI run that
    /// settled this reported `GetQueueStatus` = `0x400040` with `PeekMessageW`
    /// (`PM_NOREMOVE`) answering `None` in the same breath. MSDN says as much in
    /// its own caveat — the presence of a `QS_` flag does not guarantee that a
    /// subsequent `PeekMessage` will return a message. So a wait that includes
    /// `QS_SENDMESSAGE` returns immediately, every time, and no amount of
    /// draining fixes it because there is nothing retrievable to drain.
    ///
    /// # What it costs, stated rather than glossed
    ///
    /// A sent message that arrives *while* this thread is asleep no longer wakes
    /// it; it waits out the timeout and is dispatched by the next
    /// `drain_messages`. That is the trade this constant makes, and it is the
    /// reason `SendMessageTimeout` exists — a well-behaved broadcaster does not
    /// rely on the recipient being awake.
    pub const QS_ALL_EVENTS: u32 = 0x04BF;
    /// `INFINITE`.
    pub const INFINITE: u32 = 0xFFFF_FFFF;
    /// `WAIT_OBJECT_0` — the first handle was signalled, or, with a handle
    /// count of zero, a message is available. With `n` handles a message is
    /// `WAIT_OBJECT_0 + n`.
    pub const WAIT_OBJECT_0: u32 = 0;
    /// `CREATE_WAITABLE_TIMER_HIGH_RESOLUTION` — a timer that fires to the
    /// hundred-nanosecond due time rather than on the next system clock tick.
    /// Windows 10 1803 and later; refused as an invalid parameter before that.
    pub const CREATE_WAITABLE_TIMER_HIGH_RESOLUTION: u32 = 0x0000_0002;
    /// `TIMER_MODIFY_STATE | SYNCHRONIZE` — enough to set a timer and wait on it.
    pub const TIMER_SET_AND_WAIT: u32 = 0x0000_0002 | 0x0010_0000;
    /// `WAIT_TIMEOUT` — the wait slept for its whole timeout, which is the
    /// outcome [`ShellCaps::EVENT_WAIT`](crate::ShellCaps::EVENT_WAIT) claims is
    /// reachable.
    pub const WAIT_TIMEOUT: u32 = 258;
    /// `WAIT_FAILED`. `GetLastError` says why, and a wait that fails returns
    /// *immediately* — which is indistinguishable from a wait that woke, unless
    /// the return value is read.
    pub const WAIT_FAILED: u32 = 0xFFFF_FFFF;

    /// `HTCLIENT` — the `WM_SETCURSOR` hit-test code for the drawable area.
    ///
    /// Every other value is a piece of the frame the *system* owns a cursor
    /// for: the resize arrows on a border, the arrow over the caption. Setting
    /// ours for those would replace a working resize affordance with an arrow.
    pub const HT_CLIENT: u32 = 1;

    /// `TME_LEAVE`.
    pub const TME_LEAVE: u32 = 0x0000_0002;

    /// `SC_KEYMENU` — the `WM_SYSCOMMAND` that opens the window menu from the
    /// keyboard.
    pub const SC_KEY_MENU: usize = 0xF100;
    /// The bits of a `WM_SYSCOMMAND`'s `wParam` that name the command; the low
    /// four are the system's own.
    pub const SC_COMMAND_MASK: usize = 0xFFF0;

    /// `XBUTTON1` — the `wParam` high word of a `WM_XBUTTON*`, "back".
    pub const XBUTTON1: u32 = 0x0001;
    /// `XBUTTON2` — "forward".
    pub const XBUTTON2: u32 = 0x0002;

    /// `WHEEL_DELTA` — one detent of a notched wheel.
    ///
    /// A high-resolution wheel reports fractions of it, which is why the
    /// division that produces
    /// [`ScrollDelta::Lines`](crcbl_core::input::ScrollDelta::Lines) is done in
    /// floating point rather than as an integer count of detents.
    ///
    /// `i16` because that is the width the message carries it in, and because
    /// it converts to `f32` losslessly — a widening cast on the divisor is the
    /// kind of thing that goes unnoticed until a lint changes.
    pub const WHEEL_DELTA: i16 = 120;

    /// `PT_TOUCH` — the `POINTER_INPUT_TYPE` `GetPointerType` answers for a
    /// finger. Pen, touchpad and mouse pointers have their own values and are
    /// left to the legacy mouse messages `DefWindowProc` synthesizes from them.
    pub const PT_TOUCH: u32 = 2;
    /// `POINTER_MESSAGE_FLAG_INCONTACT`, in the high word of a pointer
    /// message's `wParam`.
    pub const POINTER_MESSAGE_FLAG_IN_CONTACT: u32 = 0x0004;
    /// `POINTER_MESSAGE_FLAG_PRIMARY` — the first contact of the interaction,
    /// the only one the system turns into mouse messages.
    pub const POINTER_MESSAGE_FLAG_PRIMARY: u32 = 0x2000;
    /// `POINTER_MESSAGE_FLAG_CANCELED` — the system took the gesture away, so
    /// this `WM_POINTERUP` is not a completed touch.
    pub const POINTER_MESSAGE_FLAG_CANCELED: u32 = 0x8000;

    /// `HID_USAGE_PAGE_GENERIC`.
    pub const HID_USAGE_PAGE_GENERIC: u16 = 0x01;
    /// `HID_USAGE_GENERIC_MOUSE`.
    pub const HID_USAGE_GENERIC_MOUSE: u16 = 0x02;
    /// `HID_USAGE_GENERIC_KEYBOARD`.
    pub const HID_USAGE_GENERIC_KEYBOARD: u16 = 0x06;
    /// `RIDEV_DEVNOTIFY` — deliver `WM_INPUT_DEVICE_CHANGE` when a device of
    /// this usage arrives or leaves.
    pub const RIDEV_DEV_NOTIFY: u32 = 0x0000_2000;
    /// `RID_INPUT` — ask `GetRawInputData` for the report rather than its
    /// header.
    pub const RID_INPUT: u32 = 0x1000_0003;
    /// `RIDI_DEVICENAME` — ask `GetRawInputDeviceInfoW` for the device's
    /// interface path, which outlives the handle across a replug.
    pub const RIDI_DEVICE_NAME: u32 = 0x2000_0007;
    /// `RIM_TYPEMOUSE`.
    pub const RIM_TYPE_MOUSE: u32 = 0;
    /// `RIM_TYPEKEYBOARD`.
    pub const RIM_TYPE_KEYBOARD: u32 = 1;
    /// `RI_KEY_BREAK` — the report is a release.
    pub const RI_KEY_BREAK: u16 = 0x0001;
    /// `RI_KEY_E0` — the scan code carries the `E0` prefix.
    pub const RI_KEY_E0: u16 = 0x0002;
    /// `RI_KEY_E1` — the scan code carries the `E1` prefix (Pause alone).
    pub const RI_KEY_E1: u16 = 0x0004;
    /// `RI_MOUSE_LEFT_BUTTON_DOWN`; each button's up edge is the next bit.
    pub const RI_MOUSE_LEFT_BUTTON_DOWN: u16 = 0x0001;
    /// `RI_MOUSE_RIGHT_BUTTON_DOWN`.
    pub const RI_MOUSE_RIGHT_BUTTON_DOWN: u16 = 0x0004;
    /// `RI_MOUSE_MIDDLE_BUTTON_DOWN`.
    pub const RI_MOUSE_MIDDLE_BUTTON_DOWN: u16 = 0x0010;
    /// `RI_MOUSE_BUTTON_4_DOWN` — `XBUTTON1`, "back".
    pub const RI_MOUSE_BUTTON_4_DOWN: u16 = 0x0040;
    /// `RI_MOUSE_BUTTON_5_DOWN` — `XBUTTON2`, "forward".
    pub const RI_MOUSE_BUTTON_5_DOWN: u16 = 0x0100;
    /// `RI_MOUSE_WHEEL`.
    pub const RI_MOUSE_WHEEL: u16 = 0x0400;
    /// `RI_MOUSE_HWHEEL`.
    pub const RI_MOUSE_H_WHEEL: u16 = 0x0800;
    /// `GIDC_REMOVAL` — the `wParam` of a `WM_INPUT_DEVICE_CHANGE` for a device
    /// that left.
    pub const GIDC_REMOVAL: usize = 2;

    /// `GCS_COMPSTR` — the composition string changed, or the index that reads
    /// it.
    pub const GCS_COMP_STR: u32 = 0x0008;
    /// `ISC_SHOWUICOMPOSITIONWINDOW` — in `WM_IME_SETCONTEXT`'s `lParam`, asks
    /// the default handler to show the input method's own composition window.
    pub const ISC_SHOW_UI_COMPOSITION_WINDOW: u32 = 0x8000_0000;
    /// `GCS_CURSORPOS` — the index that reads the cursor within it.
    pub const GCS_CURSOR_POS: u32 = 0x0080;
    /// `GCS_RESULTSTR` — the composition produced a result, or the index that
    /// reads it.
    pub const GCS_RESULT_STR: u32 = 0x0800;
    /// `IACE_DEFAULT` — give a window back its default input context.
    pub const IACE_DEFAULT: u32 = 0x0010;
    /// `CFS_DEFAULT` — the input method places its window itself.
    pub const CFS_DEFAULT: u32 = 0x0000;
    /// `CFS_POINT` — the composition window starts at `ptCurrentPos`.
    pub const CFS_POINT: u32 = 0x0002;
    /// `CFS_EXCLUDE` — the candidate list opens at `ptCurrentPos` without
    /// covering `rcArea`.
    pub const CFS_EXCLUDE: u32 = 0x0080;
    /// `MOUSE_MOVE_ABSOLUTE` — the report carries a *position*, not a delta.
    ///
    /// Set by a remote-desktop session, a tablet and some virtual machines. A
    /// backend that assumes relative motion reads a screen coordinate as a
    /// delta, which sends the camera to the far wall on the first event.
    pub const MOUSE_MOVE_ABSOLUTE: u16 = 0x0001;
    /// `MOUSE_VIRTUAL_DESKTOP` — an absolute report normalized over the whole
    /// virtual desktop rather than over the primary monitor.
    pub const MOUSE_VIRTUAL_DESKTOP: u16 = 0x0002;
    /// The range an absolute [`RawMouse`](super::RawMouse) coordinate is
    /// normalized to.
    pub const ABSOLUTE_RANGE: i32 = 65_535;

    /// `SM_CXSCREEN`.
    pub const SM_CX_SCREEN: i32 = 0;
    /// `SM_CYSCREEN`.
    pub const SM_CY_SCREEN: i32 = 1;
    /// `SM_XVIRTUALSCREEN` — the virtual screen's left edge, which is
    /// **negative** whenever a secondary monitor sits to the left of the
    /// primary. A virtual screen assumed to start at the origin is the reason a
    /// multi-monitor rectangle test passes on one desk and fails on another.
    ///
    /// Test-only, with the two extents below it: the backend never needs the
    /// desktop's origin, because `ClipCursor` clamps to it without being asked.
    /// A test that has to predict the clamp does.
    #[cfg(test)]
    pub const SM_X_VIRTUAL_SCREEN: i32 = 76;
    /// `SM_YVIRTUALSCREEN`. See [`SM_X_VIRTUAL_SCREEN`].
    #[cfg(test)]
    pub const SM_Y_VIRTUAL_SCREEN: i32 = 77;
    /// `SM_CXVIRTUALSCREEN`.
    pub const SM_CX_VIRTUAL_SCREEN: i32 = 78;
    /// `SM_CYVIRTUALSCREEN`.
    pub const SM_CY_VIRTUAL_SCREEN: i32 = 79;
    /// `SM_CXICON` — the side of a large icon, at the system DPI.
    pub const SM_CX_ICON: i32 = 11;
    /// `SM_CXSMICON` — the side of a small icon, at the system DPI.
    pub const SM_CX_SM_ICON: i32 = 49;

    /// `RT_GROUP_ICON`, the resource type of an icon as a whole: one entry per
    /// icon, naming the images of each size inside it. Passed as an integer
    /// resource id.
    pub const RT_GROUP_ICON: usize = 14;
    /// `IMAGE_ICON`, what `LoadImageW` is asked to load.
    pub const IMAGE_ICON: u32 = 1;
    /// `LOAD_LIBRARY_AS_DATAFILE | LOAD_LIBRARY_AS_IMAGE_RESOURCE`: a module
    /// mapped for its resources alone, with none of its code run.
    #[cfg(test)]
    pub const LOAD_AS_RESOURCES: u32 = 0x0000_0022;

    /// `CF_UNICODETEXT` — UTF-16, NUL-terminated, and the only text format
    /// worth writing.
    ///
    /// The system **synthesizes** `CF_TEXT` and `CF_OEMTEXT` from it on demand
    /// and synthesizes it back from them, which is why this backend has no
    /// equivalent of X11's `TARGETS` negotiation for text: Windows does that
    /// negotiation itself, in the window station, for the one format everybody
    /// agrees on.
    pub const CF_UNICODETEXT: u32 = 13;

    /// `CF_HDROP` — a file list, the block behind an `HDROP`, which is what
    /// Explorer's "copy" puts on the clipboard. Read with `DragQueryFileW`,
    /// exactly as a `WM_DROPFILES` handle is.
    pub const CF_HDROP: u32 = 15;

    /// `GMEM_MOVEABLE` — the allocation flag `SetClipboardData` requires.
    ///
    /// A clipboard payload is handed to the *system*, which may move or discard
    /// it, so it is reached through `GlobalLock` rather than as a pointer.
    pub const GMEM_MOVEABLE: u32 = 0x0002;

    /// The `iFile` that asks `DragQueryFileW` for the file **count** rather
    /// than for a path. `0xFFFFFFFF` in the SDK, where the parameter is a
    /// `UINT`.
    pub const DRAG_QUERY_COUNT: u32 = 0xFFFF_FFFF;

    /// `MAPVK_VK_TO_CHAR` — the unshifted character a virtual key produces in
    /// the current layout, with no dead-key side effect.
    pub const MAPVK_VK_TO_CHAR: u32 = 2;
    /// `MAPVK_VK_TO_VSC_EX` — the scan code a virtual key sits on in the
    /// current layout, with an `E0` or `E1` prefix in the high byte where the
    /// call knows one.
    pub const MAPVK_VK_TO_VSC_EX: u32 = 4;

    /// `VK_SHIFT`-adjacent virtual keys, left and right told apart.
    ///
    /// The AltGr disambiguation in
    /// [`keys::modifiers`](crate::win32::keys::modifiers) depends on seeing
    /// *which* Control is down, so it reads these first and the unsided
    /// [`VK_SHIFT`]/[`VK_CONTROL`]/[`VK_MENU`] only where they add a key.
    pub const VK_L_SHIFT: usize = 0xA0;
    /// See [`VK_L_SHIFT`].
    pub const VK_R_SHIFT: usize = 0xA1;
    /// See [`VK_L_SHIFT`].
    pub const VK_L_CONTROL: usize = 0xA2;
    /// See [`VK_L_SHIFT`].
    pub const VK_R_CONTROL: usize = 0xA3;
    /// See [`VK_L_SHIFT`]. `VK_MENU` is Windows' name for Alt.
    pub const VK_L_MENU: usize = 0xA4;
    /// See [`VK_L_SHIFT`].
    pub const VK_R_MENU: usize = 0xA5;
    /// `VK_SHIFT`: either Shift, which Windows sets with a sided one and
    /// alone for a key injected by this unsided virtual key.
    pub const VK_SHIFT: usize = 0x10;
    /// `VK_CONTROL`. See [`VK_SHIFT`].
    pub const VK_CONTROL: usize = 0x11;
    /// `VK_MENU`: Alt. See [`VK_SHIFT`].
    pub const VK_MENU: usize = 0x12;
    /// `VK_LWIN`.
    pub const VK_L_WIN: usize = 0x5B;
    /// `VK_RWIN`.
    pub const VK_R_WIN: usize = 0x5C;
    /// `VK_CAPITAL` — Caps Lock, read for its *toggle* bit.
    pub const VK_CAPITAL: usize = 0x14;
    /// `VK_NUMLOCK`, likewise.
    pub const VK_NUM_LOCK: usize = 0x90;
    /// `VK_PROCESSKEY` — the virtual key a `WM_KEYDOWN` carries in place of
    /// the real one when an input method consumed the keystroke. A `u16`
    /// because it is compared with a key message's `wParam`, not used as an
    /// index into a keyboard-state snapshot.
    pub const VK_PROCESS_KEY: u16 = 0xE5;

    /// The `WMSZ_*` edge a `WM_SIZING` is being dragged by.
    pub const WMSZ_LEFT: usize = 1;
    /// See [`WMSZ_LEFT`].
    pub const WMSZ_RIGHT: usize = 2;
    /// See [`WMSZ_LEFT`].
    pub const WMSZ_TOP: usize = 3;
    /// See [`WMSZ_LEFT`].
    pub const WMSZ_TOP_LEFT: usize = 4;
    /// See [`WMSZ_LEFT`].
    pub const WMSZ_TOP_RIGHT: usize = 5;
    /// See [`WMSZ_LEFT`].
    pub const WMSZ_BOTTOM: usize = 6;
    /// See [`WMSZ_LEFT`].
    pub const WMSZ_BOTTOM_LEFT: usize = 7;
    /// See [`WMSZ_LEFT`].
    pub const WMSZ_BOTTOM_RIGHT: usize = 8;
}

// ---------------------------------------------------------------------------
// The imports
// ---------------------------------------------------------------------------

// The `user32` surface: window classes, windows, messages, monitors and DPI.
#[cfg(target_os = "windows")]
#[link(name = "user32")]
unsafe extern "system" {
    pub fn RegisterClassExW(class: *const WndClassExW) -> u16;
    pub fn CreateWindowExW(
        ex_style: u32,
        class_name: *const u16,
        window_name: *const u16,
        style: u32,
        x: i32,
        y: i32,
        width: i32,
        height: i32,
        parent: Handle,
        menu: Handle,
        instance: Handle,
        param: *mut c_void,
    ) -> Handle;
    pub fn DestroyWindow(hwnd: Handle) -> Bool32;
    pub fn DefWindowProcW(hwnd: Handle, message: u32, w_param: Wparam, l_param: Lparam) -> Lresult;
    pub fn GetWindowLongPtrW(hwnd: Handle, index: i32) -> isize;
    pub fn SetWindowLongPtrW(hwnd: Handle, index: i32, value: isize) -> isize;
    pub fn ShowWindow(hwnd: Handle, command: i32) -> Bool32;
    pub fn IsWindowVisible(hwnd: Handle) -> Bool32;
    pub fn IsIconic(hwnd: Handle) -> Bool32;
    pub fn SetWindowTextW(hwnd: Handle, text: *const u16) -> Bool32;
    pub fn SetWindowPos(
        hwnd: Handle,
        insert_after: Handle,
        x: i32,
        y: i32,
        width: i32,
        height: i32,
        flags: u32,
    ) -> Bool32;
    pub fn GetWindowPlacement(hwnd: Handle, placement: *mut WindowPlacement) -> Bool32;
    pub fn SetWindowPlacement(hwnd: Handle, placement: *const WindowPlacement) -> Bool32;
    pub fn GetClientRect(hwnd: Handle, rect: *mut Rect) -> Bool32;
    pub fn AdjustWindowRectExForDpi(
        rect: *mut Rect,
        style: u32,
        menu: Bool32,
        ex_style: u32,
        dpi: u32,
    ) -> Bool32;
    pub fn PeekMessageW(
        message: *mut Msg,
        hwnd: Handle,
        filter_min: u32,
        filter_max: u32,
        remove: u32,
    ) -> Bool32;
    /// Turns a virtual-key message into the `WM_CHAR` the layout says it
    /// produces, and posts it back to the front of this thread's queue.
    ///
    /// **The one call in the pump that is not about delivery.** A `WM_KEYDOWN`
    /// says which key went down; the *character* it produces — dead keys
    /// composed, AltGr applied, an IME's committed string — exists only because
    /// this ran. Without it `WM_CHAR` is never generated for a real keystroke
    /// and the whole [`Char`](super::events::RawEvent::Char) path is
    /// unreachable, however well tested it is by hand.
    pub fn TranslateMessage(message: *const Msg) -> Bool32;
    pub fn DispatchMessageW(message: *const Msg) -> Lresult;
    // Test-only: the two synchronous messages this backend answers —
    // `WM_GETMINMAXINFO` and `WM_SIZING` — are otherwise only sent by a user
    // dragging a window edge, which CI cannot do. Sending them by hand is what
    // makes the constraint path testable at all.
    #[cfg(test)]
    pub fn SendMessageW(hwnd: Handle, message: u32, w_param: Wparam, l_param: Lparam) -> Lresult;
    // Test-only: a message *posted* rather than sent is the one a wait's own
    // drain dispatches, which is the case `Win32Shell::wait` returns
    // `Wake::Recorded` for.
    #[cfg(test)]
    pub fn PostMessageW(hwnd: Handle, message: u32, w_param: Wparam, l_param: Lparam) -> Bool32;
    pub fn MsgWaitForMultipleObjectsEx(
        count: u32,
        handles: *const Handle,
        milliseconds: u32,
        wake_mask: u32,
        flags: u32,
    ) -> u32;
    // Test-only, like `SendMessageW` above and for a related reason: outside a
    // test nothing knows what the queue *should* hold, so a `QS_*` reading
    // answers no question the backend can act on. Inside one it is how a wait
    // that woke when the queue was known to be empty explains itself. The high
    // word is "there is a message now", the low word "there has been one since
    // you last looked" — the distinction `MWMO_INPUTAVAILABLE` turns on.
    #[cfg(test)]
    pub fn GetQueueStatus(flags: u32) -> u32;
    pub fn MonitorFromWindow(hwnd: Handle, flags: u32) -> Handle;
    pub fn MonitorFromPoint(point: Point, flags: u32) -> Handle;
    // Where the frame is, for building an input region in window coordinates;
    // also how tests read back where a panel landed.
    pub fn GetWindowRect(hwnd: Handle, rect: *mut Rect) -> Bool32;
    pub fn EnumDisplayMonitors(
        hdc: Handle,
        clip: *const Rect,
        callback: MonitorEnumProc,
        data: Lparam,
    ) -> Bool32;
    pub fn GetMonitorInfoW(monitor: Handle, info: *mut MonitorInfoExW) -> Bool32;
    pub fn EnumDisplaySettingsW(device: *const u16, mode: u32, dev_mode: *mut DevModeW) -> Bool32;
    // The exact refresh rate: `QueryDisplayConfig`'s `DISPLAYCONFIG_RATIONAL`
    // carries 60000/1001 where `EnumDisplaySettingsW` reports the integer 60.
    // `GetDisplayConfigBufferSizes` sizes the two arrays the query fills, and
    // `DisplayConfigGetDeviceInfo` names each path's source so a monitor's
    // `\\.\DISPLAYn` can be matched to its mode.
    pub fn GetDisplayConfigBufferSizes(
        flags: u32,
        path_count: *mut u32,
        mode_count: *mut u32,
    ) -> i32;
    pub fn QueryDisplayConfig(
        flags: u32,
        path_count: *mut u32,
        paths: *mut DisplayConfigPathInfo,
        mode_count: *mut u32,
        modes: *mut DisplayConfigModeInfo,
        topology: *mut u32,
    ) -> i32;
    pub fn DisplayConfigGetDeviceInfo(request: *mut DisplayConfigDeviceInfoHeader) -> i32;
    pub fn GetDpiForWindow(hwnd: Handle) -> u32;
    pub fn SetProcessDpiAwarenessContext(context: isize) -> Bool32;
    pub fn LoadCursorW(instance: Handle, name: usize) -> Handle;
    // The time of the message currently being processed, on the same
    // `GetTickCount` clock as `Msg::time`. A window procedure is not handed its
    // message's `MSG`, so this is the only way to stamp an event from inside
    // one — see `TimeBase`.
    pub fn GetMessageTime() -> i32;
    pub fn TrackMouseEvent(track: *mut TrackMouse) -> Bool32;
    pub fn SetCapture(hwnd: Handle) -> Handle;
    pub fn ReleaseCapture() -> Bool32;
    // A null rectangle *releases* the clip, which is the call that must run
    // when a window loses focus. See `input` for why that is not optional.
    pub fn ClipCursor(rect: *const Rect) -> Bool32;
    // Test-only: the clip is otherwise invisible from inside the process that
    // set it, and "the pointer is confined" is a claim about the *system's*
    // state rather than about a field this backend keeps. Reading it back is
    // what makes the confinement tests able to fail.
    #[cfg(test)]
    pub fn GetClipCursor(rect: *mut Rect) -> Bool32;
    // A panel that takes the keyboard asks for the foreground with this. The
    // tests use it too: `ClipCursor` and `SetCursorPos` are restricted to the
    // process that owns the foreground window, and CI has nobody to click on
    // ours. This is the click.
    pub fn SetForegroundWindow(hwnd: Handle) -> Bool32;
    // The other half of that request: `SetForegroundWindow` can be refused,
    // answer success while the foreground lock leaves another process in
    // front, or be honoured and then overtaken, and none of it shows up in
    // anything this backend keeps. A panel asks this afterwards to know whether
    // the foreground is really its own (see `panel::foreground_granted`), and
    // the tests ask it to confirm the foreground they depend on.
    pub fn GetForegroundWindow() -> Handle;
    // The window of this thread holding the keyboard focus, or null. Read once,
    // when a window's accessibility adapter is made: a window shown as it is
    // created takes the focus before the adapter exists to hear it.
    #[cfg(feature = "accesskit")]
    pub fn GetFocus() -> Handle;
    pub fn ClientToScreen(hwnd: Handle, point: *mut Point) -> Bool32;
    pub fn ScreenToClient(hwnd: Handle, point: *mut Point) -> Bool32;
    // The region is in window coordinates, frame included. On success the
    // **system** owns it and frees it when the window goes or a later call
    // replaces it; on failure it stays the caller's. Null removes the region.
    pub fn SetWindowRgn(hwnd: Handle, region: Handle, redraw: Bool32) -> i32;
    // Which kind of device a `WM_POINTER*` message's pointer id belongs to.
    // Answers only while that pointer is live, which is why it is asked inside
    // the window procedure rather than at translation time.
    pub fn GetPointerType(pointer_id: u32, kind: *mut u32) -> Bool32;
    pub fn SetCursorPos(x: i32, y: i32) -> Bool32;
    pub fn GetCursorPos(point: *mut Point) -> Bool32;
    pub fn SetCursor(cursor: Handle) -> Handle;
    // Returns the new display count; the cursor is drawn while it is >= 0,
    // which is why the count has to be balanced rather than merely decremented.
    pub fn ShowCursor(show: Bool32) -> i32;
    pub fn GetKeyboardState(state: *mut u8) -> Bool32;
    pub fn MapVirtualKeyW(code: u32, map_type: u32) -> u32;
    pub fn RegisterRawInputDevices(devices: *const RawInputDevice, count: u32, size: u32)
    -> Bool32;
    pub fn GetRawInputData(
        raw_input: Handle,
        command: u32,
        data: *mut c_void,
        size: *mut u32,
        header_size: u32,
    ) -> u32;
    // With `RIDI_DEVICENAME`, `size` is in **characters**, not bytes, and a
    // null `data` asks for the length the name needs.
    pub fn GetRawInputDeviceInfoW(
        device: Handle,
        command: u32,
        data: *mut c_void,
        size: *mut u32,
    ) -> u32;
    pub fn GetSystemMetrics(index: i32) -> i32;
    // The executable's own icon for the window class; see `window::module_icon`.
    pub fn LoadImageW(
        instance: Handle,
        name: *const u16,
        kind: u32,
        width: i32,
        height: i32,
        flags: u32,
    ) -> Handle;
    #[cfg(test)]
    pub fn DestroyIcon(icon: Handle) -> Bool32;
    // The clipboard. `OpenClipboard` **fails while another process has it
    // open**, which is routine rather than exceptional, so every one of these
    // is reached through the guard in `win32::clipboard` and never directly.
    // A registered format id is an atom in the window station's table, is the
    // same number for the same name in every process, and is what carries a
    // mime type Windows has no `CF_*` for.
    pub fn RegisterClipboardFormatW(name: *const u16) -> u32;
    pub fn OpenClipboard(hwnd: Handle) -> Bool32;
    pub fn CloseClipboard() -> Bool32;
    pub fn EmptyClipboard() -> Bool32;
    // Ownership of the handle passes to the **system** on success, and stays
    // ours on failure — the asymmetry the guard exists to get right.
    pub fn SetClipboardData(format: u32, mem: Handle) -> Handle;
    // The returned handle belongs to the clipboard: it must not be freed, and
    // it is valid only until `CloseClipboard`.
    pub fn GetClipboardData(format: u32) -> Handle;
    // Test-only: "the clipboard was closed on every path out" is a claim about
    // the *system's* state, not about a field this backend keeps, and this is
    // the only thing that can see it. Null means nobody has it open.
    #[cfg(test)]
    pub fn GetOpenClipboardWindow() -> Handle;
}

// The `shell32` surface: file drops, and nothing else.
//
// The fifth system library, on the same terms as `shcore` above — `shell32.dll`
// is present on every Windows this backend can run on, so there is nothing for
// a runtime probe to discover. It is here because `WM_DROPFILES` hands over an
// `HDROP`, which is a shell object rather than a window-manager one: only these
// four calls can read it, and the alternative is parsing the `DROPFILES`
// structure by hand, which means owning the `fWide` ANSI case that shell32
// already owns. See `win32::dnd`.
#[cfg(target_os = "windows")]
#[link(name = "shell32")]
unsafe extern "system" {
    // Sets or clears `WS_EX_ACCEPTFILES`; see `style::EX_ACCEPT_FILES` for why
    // that matters to anything that rewrites the extended style word.
    pub fn DragAcceptFiles(hwnd: Handle, accept: Bool32);
    // Returns a message-specific value; `ABM_NEW` and `ABM_REMOVE` answer
    // `TRUE` on success, and `ABM_QUERYPOS` and `ABM_SETPOS` write `data.rc`.
    pub fn SHAppBarMessage(message: u32, data: *mut AppBarData) -> usize;
    // With `DRAG_QUERY_COUNT` it answers the number of files and writes
    // nothing; with an index and a null buffer it answers the length in
    // characters, excluding the terminator; with an index and a buffer it
    // copies and answers how much it copied.
    pub fn DragQueryFileW(hdrop: Handle, index: u32, buffer: *mut u16, size: u32) -> u32;
    // Where in the window's **client** area the drop happened.
    pub fn DragQueryPoint(hdrop: Handle, point: *mut Point) -> Bool32;
    // Releases the `HDROP`. Not optional: the memory is the shell's and is
    // leaked without it.
    pub fn DragFinish(hdrop: Handle);
}

// The `imm32` surface: the input method's composition string, and where its
// windows go. A Text Services Framework IME reaches a window that is not
// TSF-aware through these same calls, so this is the whole surface for both.
#[cfg(target_os = "windows")]
#[link(name = "imm32")]
unsafe extern "system" {
    // Null for a window whose thread has no input context; released with
    // `ImmReleaseContext` by whoever took it.
    pub fn ImmGetContext(hwnd: Handle) -> Handle;
    pub fn ImmReleaseContext(hwnd: Handle, context: Handle) -> Bool32;
    // With a null buffer it answers the size in **bytes**; with a buffer it
    // copies and answers how many bytes it copied. `GCS_CURSORPOS` answers the
    // cursor as a code unit index and copies nothing.
    pub fn ImmGetCompositionStringW(
        context: Handle,
        index: u32,
        buffer: *mut c_void,
        size: u32,
    ) -> i32;
    pub fn ImmSetCompositionWindow(context: Handle, form: *const CompositionForm) -> Bool32;
    pub fn ImmSetCandidateWindow(context: Handle, form: *const CandidateForm) -> Bool32;
    // With a null context and no flags it leaves the window with no input
    // context, which keeps the input method out of it; `IACE_DEFAULT` gives
    // the window back its thread's default context.
    pub fn ImmAssociateContextEx(hwnd: Handle, context: Handle, flags: u32) -> Bool32;
}

// The `dwmapi` surface: one call, for the frame of a transparent window. On
// the same terms as `shcore`: the library is part of every Windows this backend
// runs on. An attribute the running Windows does not know is refused with
// `E_INVALIDARG`, which is a result, not a missing symbol.
#[cfg(target_os = "windows")]
#[link(name = "dwmapi")]
unsafe extern "system" {
    // An `HRESULT`; reads `size` bytes from `value`.
    pub fn DwmSetWindowAttribute(
        hwnd: Handle,
        attribute: u32,
        value: *const c_void,
        size: u32,
    ) -> i32;
}

// The `gdi32` surface: the class background brush, and the regions a window's
// input region is built from.
#[cfg(target_os = "windows")]
#[link(name = "gdi32")]
unsafe extern "system" {
    pub fn GetStockObject(object: i32) -> Handle;
    // Null when the system is out of GDI objects. The far edges are exclusive.
    pub fn CreateRectRgn(left: i32, top: i32, right: i32, bottom: i32) -> Handle;
    // Writes the combination into `destination`, which must already exist,
    // and answers the result's complexity, or `ERROR`.
    pub fn CombineRgn(destination: Handle, first: Handle, second: Handle, mode: i32) -> i32;
    pub fn DeleteObject(object: Handle) -> Bool32;
}

// The `shcore` surface: per-monitor DPI. `GetDpiForMonitor` lives here rather
// than in `user32` because it arrived with Windows 8.1's shell rather than with
// 1607's window manager. It is the per-*monitor* counterpart of
// `GetDpiForWindow`, and it is needed because a `MonitorInfo` has a scale
// factor even when no window of ours is on that monitor.
#[cfg(target_os = "windows")]
#[link(name = "shcore")]
unsafe extern "system" {
    pub fn GetDpiForMonitor(
        monitor: Handle,
        dpi_type: i32,
        dpi_x: *mut u32,
        dpi_y: *mut u32,
    ) -> i32;
}

// The `kernel32` surface.
#[cfg(target_os = "windows")]
#[link(name = "kernel32")]
unsafe extern "system" {
    pub fn GetModuleHandleW(name: *const u16) -> Handle;
    pub fn GetLastError() -> u32;
    // A module's resources, for the icon the window class takes from the
    // executable. The callback runs inside the call, once per name, and
    // returning zero stops the walk.
    pub fn EnumResourceNamesW(
        module: Handle,
        kind: *const u16,
        callback: EnumResNameProc,
        param: Lparam,
    ) -> Bool32;
    #[cfg(test)]
    pub fn LoadLibraryExW(name: *const u16, file: Handle, flags: u32) -> Handle;
    #[cfg(test)]
    pub fn FreeLibrary(module: Handle) -> Bool32;
    // The clipboard's payloads. A `GMEM_MOVEABLE` block has no address until it
    // is locked, and the lock count has to be balanced exactly as
    // `ShowCursor`'s does — an unbalanced one pins a block the system wants to
    // move for as long as the process lives.
    pub fn GlobalAlloc(flags: u32, bytes: usize) -> Handle;
    pub fn GlobalFree(mem: Handle) -> Handle;
    pub fn GlobalLock(mem: Handle) -> *mut c_void;
    pub fn GlobalUnlock(mem: Handle) -> Bool32;
    // May answer **more** than was asked for: the documented contract is that a
    // block is at least the requested size. See `win32::clipboard` for what
    // that means for a payload read back.
    pub fn GlobalSize(mem: Handle) -> usize;
    // Milliseconds since the system started, 64-bit: the clock `MSG::time` is
    // on. See `TimeBase` for why that makes Win32's timestamp rebasing the
    // easiest of the native backends' and still not free.
    pub fn GetTickCount64() -> u64;
    // The high-resolution timer `wait_events` sleeps on, so a short timeout is
    // not rounded up to the next clock tick. `due` is in 100 ns units and
    // negative for "relative to now".
    pub fn CreateWaitableTimerExW(
        attributes: *const c_void,
        name: *const u16,
        flags: u32,
        access: u32,
    ) -> Handle;
    pub fn SetWaitableTimer(
        timer: Handle,
        due: *const i64,
        period: i32,
        completion: *const c_void,
        argument: *const c_void,
        resume: Bool32,
    ) -> Bool32;
    pub fn CloseHandle(handle: Handle) -> Bool32;
    // The doorbell a `ShellWaker` rings from another thread: an auto-reset
    // event in the handle set `wait_events` waits on. See `win32::wake`.
    pub fn CreateEventW(
        attributes: *const c_void,
        manual_reset: Bool32,
        initial_state: Bool32,
        name: *const u16,
    ) -> Handle;
    pub fn SetEvent(event: Handle) -> Bool32;
}

// ---------------------------------------------------------------------------
// Small helpers over the imports
// ---------------------------------------------------------------------------

/// A Rust string as a NUL-terminated UTF-16 buffer, or `None` if it contains an
/// interior NUL.
///
/// Every `*W` entry point takes a NUL-terminated string, so an interior NUL
/// silently truncates rather than failing — a window titled `"save\0nothing"`
/// would appear as `"save"` in the taskbar with no error anywhere. The two
/// Linux backends reject the same input for the same reason, so the seam gives
/// one answer on every platform.
pub fn wide(text: &str) -> Option<Vec<u16>> {
    if text.as_bytes().contains(&0) {
        return None;
    }
    let mut buffer: Vec<u16> = text.encode_utf16().collect();
    buffer.push(0);
    Some(buffer)
}

/// `CLOCK`-equivalent: system uptime in nanoseconds.
///
/// `GetTickCount64` rather than `QueryPerformanceCounter`, and deliberately:
/// [`Msg::time`] is a `GetTickCount` value, so this is the clock the events
/// this backend has to rebase are already on. Reading a *different*, higher
/// resolution clock and subtracting a tick count from it would introduce an
/// error of up to one tick period (about 15.6 ms by default) into every
/// timestamp, in exchange for precision the source data does not have.
#[cfg(target_os = "windows")]
pub fn tick_nanos() -> u64 {
    // SAFETY: `GetTickCount64` takes no arguments, reads no memory and cannot
    // fail; it is available on every Windows this backend supports.
    unsafe { GetTickCount64() }.saturating_mul(1_000_000)
}

#[cfg(test)]
mod tests {
    use super::*;

    /// The width of the field `select` picks out, read from its type alone —
    /// the function is never called.
    fn field_size<T, F>(_select: fn(&T) -> &F) -> usize {
        size_of::<F>()
    }

    /// Asserts a structure's size and every field's offset and width, one
    /// `field: offset, width;` row per field.
    ///
    /// The destructuring pattern names every row's field and has no `..`, so a
    /// field added to the declaration without a row here fails to compile
    /// rather than going unchecked.
    macro_rules! assert_layout {
        ($ty:ident, $size:literal, { $($field:ident: $offset:literal, $width:literal;)+ }) => {{
            let _every_field_has_a_row: fn($ty) = |value| {
                let $ty { $($field: _),+ } = value;
            };
            assert_eq!(size_of::<$ty>(), $size, concat!("size of ", stringify!($ty)));
            $(
                assert_eq!(
                    core::mem::offset_of!($ty, $field),
                    $offset,
                    concat!("offset of ", stringify!($ty), "::", stringify!($field))
                );
                assert_eq!(
                    field_size(|value: &$ty| &value.$field),
                    $width,
                    concat!("width of ", stringify!($ty), "::", stringify!($field))
                );
            )+
        }};
    }

    /// The layouts, field by field, against what `windows.h` produces on x64.
    ///
    /// Every number is the SDK's own `sizeof`/`offsetof` for the matching
    /// field, printed by a C program built with MSVC 19.44 (`_MSC_FULL_VER`
    /// 194435229) against Windows SDK 10.0.26100.0 for x64. They are the x64
    /// Windows ABI, fixed by it rather than by anything in this crate. Where
    /// the Rust declaration flattens a C union into one field, the row is the
    /// union's extent; where it names bytes C leaves anonymous, the row is
    /// that gap.
    ///
    /// Checking every field's offset, not only the size, is what catches two
    /// same-width fields declared in the wrong order: the size is unchanged,
    /// and each would read the other's value.
    ///
    /// A field of the right width and the wrong type — `u32` where the SDK has
    /// `LONG` — passes here. On Windows, `sdk_layout` checks every field's type,
    /// down the arms of each union flattened here, against the `windows`
    /// crate's declarations, which are generated from Windows' own metadata.
    ///
    /// These run on the host as well as on Windows, because every field is a
    /// fixed-width type or a pointer and 64-bit Linux lays them out
    /// identically — which is the point: a padding mistake in [`DevModeW`]
    /// would read the refresh rate from the wrong offset and report a
    /// plausible number, and that is not something a Windows-only test would
    /// have caught any better.
    #[test]
    fn the_structures_match_the_c_layout() {
        assert_layout!(Rect, 16, {
            left: 0, 4;
            top: 4, 4;
            right: 8, 4;
            bottom: 12, 4;
        });
        assert_layout!(Point, 8, {
            x: 0, 4;
            y: 4, 4;
        });
        assert_layout!(Msg, 48, {
            hwnd: 0, 8;
            message: 8, 4;
            w_param: 16, 8;
            l_param: 24, 8;
            time: 32, 4;
            pt: 36, 8;
            // C's tail padding; see the type docs.
            l_private: 44, 4;
        });
        assert_layout!(WndClassExW, 80, {
            cb_size: 0, 4;
            style: 4, 4;
            lpfn_wnd_proc: 8, 8;
            cb_cls_extra: 16, 4;
            cb_wnd_extra: 20, 4;
            h_instance: 24, 8;
            h_icon: 32, 8;
            h_cursor: 40, 8;
            hbr_background: 48, 8;
            lpsz_menu_name: 56, 8;
            lpsz_class_name: 64, 8;
            h_icon_sm: 72, 8;
        });
        assert_layout!(CreateStructW, 80, {
            lp_create_params: 0, 8;
            h_instance: 8, 8;
            h_menu: 16, 8;
            hwnd_parent: 24, 8;
            cy: 32, 4;
            cx: 36, 4;
            y: 40, 4;
            x: 44, 4;
            style: 48, 4;
            lpsz_name: 56, 8;
            lpsz_class: 64, 8;
            dw_ex_style: 72, 4;
        });
        assert_layout!(MinMaxInfo, 40, {
            pt_reserved: 0, 8;
            pt_max_size: 8, 8;
            pt_max_position: 16, 8;
            pt_min_track_size: 24, 8;
            pt_max_track_size: 32, 8;
        });
        assert_layout!(WindowPlacement, 44, {
            length: 0, 4;
            flags: 4, 4;
            show_cmd: 8, 4;
            pt_min_position: 12, 8;
            pt_max_position: 20, 8;
            rc_normal_position: 28, 16;
        });
        assert_layout!(MonitorInfoExW, 104, {
            cb_size: 0, 4;
            rc_monitor: 4, 16;
            rc_work: 20, 16;
            dw_flags: 36, 4;
            sz_device: 40, 64;
        });
        // The one with two unions in it, and the one whose fields are read
        // past the padding.
        assert_layout!(DevModeW, 220, {
            dm_device_name: 0, 64;
            dm_spec_version: 64, 2;
            dm_driver_version: 66, 2;
            dm_size: 68, 2;
            dm_driver_extra: 70, 2;
            dm_fields: 72, 4;
            // The printer/display union's display arm. The probe printed the
            // union's extent, 76 for 16 bytes; these rows split it at the
            // arm's members, which `sdk_layout` checks against the SDK.
            dm_position: 76, 8;
            dm_display_orientation: 84, 4;
            dm_display_fixed_output: 88, 4;
            dm_color: 92, 2;
            dm_duplex: 94, 2;
            dm_y_resolution: 96, 2;
            dm_tt_option: 98, 2;
            dm_collate: 100, 2;
            dm_form_name: 102, 64;
            dm_log_pixels: 166, 2;
            dm_bits_per_pel: 168, 4;
            dm_pels_width: 172, 4;
            dm_pels_height: 176, 4;
            // `dmDisplayFlags` / `dmNup`.
            dm_display_flags: 180, 4;
            dm_display_frequency: 184, 4;
            dm_icm_method: 188, 4;
            dm_icm_intent: 192, 4;
            dm_media_type: 196, 4;
            dm_dither_type: 200, 4;
            dm_reserved1: 204, 4;
            dm_reserved2: 208, 4;
            dm_panning_width: 212, 4;
            dm_panning_height: 216, 4;
        });

        // The `QueryDisplayConfig` structures, read for the exact refresh
        // rate. A wrong one reads a plausible wrong rate: an offset mistake in
        // `DisplayConfigVideoSignalInfo` would report 59.94 Hz as something
        // only a CRT ran at, and the whole point of asking `QueryDisplayConfig`
        // is that `EnumDisplaySettingsW` already rounds.
        assert_layout!(Luid, 8, {
            low_part: 0, 4;
            high_part: 4, 4;
        });
        assert_layout!(DisplayConfig2dRegion, 8, {
            cx: 0, 4;
            cy: 4, 4;
        });
        assert_layout!(DisplayConfigRational, 8, {
            numerator: 0, 4;
            denominator: 4, 4;
        });
        assert_layout!(DisplayConfigVideoSignalInfo, 48, {
            pixel_rate: 0, 8;
            h_sync_freq: 8, 8;
            v_sync_freq: 16, 8;
            active_size: 24, 8;
            total_size: 32, 8;
            // `AdditionalSignalInfo` / `videoStandard`.
            additional_signal_info: 40, 4;
            scan_line_ordering: 44, 4;
        });
        assert_layout!(DisplayConfigTargetMode, 48, {
            target_video_signal_info: 0, 48;
        });
        assert_layout!(DisplayConfigModeInfo, 64, {
            info_type: 0, 4;
            id: 4, 4;
            adapter_id: 8, 8;
            // The union's `targetMode`, its largest arm: `sourceMode` and
            // `desktopImageInfo` are smaller and start at the same offset.
            target_mode: 16, 48;
        });
        assert_layout!(DisplayConfigPathSourceInfo, 20, {
            adapter_id: 0, 8;
            id: 8, 4;
            mode_info_idx: 12, 4;
            status_flags: 16, 4;
        });
        assert_layout!(DisplayConfigPathTargetInfo, 48, {
            adapter_id: 0, 8;
            id: 8, 4;
            mode_info_idx: 12, 4;
            output_technology: 16, 4;
            rotation: 20, 4;
            scaling: 24, 4;
            refresh_rate: 28, 8;
            scan_line_ordering: 36, 4;
            target_available: 40, 4;
            status_flags: 44, 4;
        });
        assert_layout!(DisplayConfigPathInfo, 72, {
            source_info: 0, 20;
            target_info: 20, 48;
            flags: 68, 4;
        });
        assert_layout!(DisplayConfigDeviceInfoHeader, 20, {
            kind: 0, 4;
            size: 4, 4;
            adapter_id: 8, 8;
            id: 16, 4;
        });
        assert_layout!(DisplayConfigSourceDeviceName, 84, {
            header: 0, 20;
            view_gdi_device_name: 20, 64;
        });

        // The input structures. `RAWMOUSE` is the one that matters: its
        // `usFlags` is followed by two bytes of union alignment, and reading
        // `lLastX` from offset 6 instead of 12 would produce a delta made of
        // half a button mask — a plausible number, never a crash.
        assert_layout!(TrackMouse, 24, {
            cb_size: 0, 4;
            dw_flags: 4, 4;
            hwnd_track: 8, 8;
            dw_hover_time: 16, 4;
        });
        assert_layout!(RawInputDevice, 16, {
            us_usage_page: 0, 2;
            us_usage: 2, 2;
            dw_flags: 4, 4;
            hwnd_target: 8, 8;
        });
        assert_layout!(RawInputHeader, 24, {
            dw_type: 0, 4;
            dw_size: 4, 4;
            h_device: 8, 8;
            w_param: 16, 8;
        });
        assert_layout!(RawMouse, 24, {
            us_flags: 0, 2;
            // The gap before the union, which C leaves unnamed.
            padding: 2, 2;
            // `ulButtons` / `usButtonFlags` + `usButtonData`.
            ul_buttons: 4, 4;
            ul_raw_buttons: 8, 4;
            l_last_x: 12, 4;
            l_last_y: 16, 4;
            ul_extra_information: 20, 4;
        });
        assert_layout!(RawKeyboard, 16, {
            make_code: 0, 2;
            flags: 2, 2;
            reserved: 4, 2;
            v_key: 6, 2;
            message: 8, 4;
            extra_information: 12, 4;
        });
        assert_layout!(RawInput, 48, {
            header: 0, 24;
            data: 24, 24;
        });
        // The union has no row table, since a union pattern names one field;
        // each arm's width is its own structure's, asserted above. `RAWHID`,
        // the arm left out, is smaller than both.
        assert_eq!(size_of::<RawInputData>(), 24);
        assert_eq!(core::mem::offset_of!(RawInput, data.mouse), 24);
        assert_eq!(core::mem::offset_of!(RawInput, data.keyboard), 24);
        assert!(size_of::<RawKeyboard>() <= size_of::<RawMouse>());

        // The input method's placement forms. These rows were printed by the
        // same kind of program against mingw-w64's `imm.h`, built by GCC 16.2
        // for x64, rather than against the Windows SDK: the x64 ABI is the
        // same either way.
        assert_layout!(CompositionForm, 28, {
            dw_style: 0, 4;
            pt_current_pos: 4, 8;
            rc_area: 12, 16;
        });
        assert_layout!(CandidateForm, 32, {
            dw_index: 0, 4;
            dw_style: 4, 4;
            pt_current_pos: 8, 8;
            rc_area: 16, 16;
        });

        // The one a *test* writes rather than reads. A wrong length here puts
        // the file list where `DragQueryFileW` does not look, and the drop test
        // would then report zero files as though the backend had lost them.
        assert_layout!(DropFiles, 20, {
            p_files: 0, 4;
            pt: 4, 8;
            f_nc: 12, 4;
            f_wide: 16, 4;
        });
    }

    #[test]
    fn the_defaults_carry_the_sizes_the_system_validates() {
        // Three structures are self-describing, and a wrong `cbSize` is
        // rejected rather than tolerated — `GetMonitorInfoW` with the plain
        // `MONITORINFO` size silently does not fill in the device name.
        assert_eq!(
            u32::from(DevModeW::default().dm_size),
            size_of::<DevModeW>() as u32
        );
        assert_eq!(
            MonitorInfoExW::default().cb_size,
            size_of::<MonitorInfoExW>() as u32
        );
    }

    #[test]
    fn a_rectangle_is_two_corners_and_never_has_a_negative_size() {
        let rect = Rect {
            left: 100,
            top: 50,
            right: 1380,
            bottom: 770,
        };
        assert_eq!(rect.width(), 1280);
        assert_eq!(rect.height(), 720);
        // Degenerate rather than negative: a window rectangle that has been
        // dragged inside out is zero-sized, and a negative width propagated
        // into a `u32` size would be four billion pixels.
        let inverted = Rect {
            left: 10,
            top: 10,
            right: 0,
            bottom: 0,
        };
        assert_eq!(inverted.width(), 0);
        assert_eq!(inverted.height(), 0);
    }

    #[test]
    fn an_intersection_is_the_overlap_and_is_degenerate_when_there_is_none() {
        // What `ClipCursor` does to a rectangle before applying it, and the
        // reason this exists: the Windows runner's display is 1024×768, which
        // is *smaller* than the default window, so the clip comes back clamped
        // and a test that asserted the client rectangle failed on real, correct
        // behaviour.
        let client = Rect {
            left: 8,
            top: 31,
            right: 1036,
            bottom: 751,
        };
        let screen = Rect {
            left: 0,
            top: 0,
            right: 1024,
            bottom: 768,
        };
        assert_eq!(
            client.intersect(screen),
            Rect {
                left: 8,
                top: 31,
                right: 1024,
                bottom: 751
            },
            "only the edge that overhangs moves"
        );
        assert_eq!(
            client.intersect(client),
            client,
            "a window that fits is not clamped at all"
        );

        // A virtual screen whose origin is negative — a second monitor to the
        // left of the primary — must not be treated as starting at zero.
        let left_monitor = Rect {
            left: -1920,
            top: 0,
            right: -900,
            bottom: 1080,
        };
        let virtual_screen = Rect {
            left: -1920,
            top: 0,
            right: 1920,
            bottom: 1080,
        };
        assert_eq!(left_monitor.intersect(virtual_screen), left_monitor);

        // Disjoint rectangles produce a degenerate one rather than a negative
        // width, which `width`/`height` already clamp.
        let elsewhere = Rect {
            left: 4_000,
            top: 4_000,
            right: 5_000,
            bottom: 5_000,
        };
        let empty = client.intersect(elsewhere);
        assert_eq!((empty.width(), empty.height()), (0, 0));
    }

    #[test]
    fn a_string_with_an_interior_nul_has_no_utf16_form() {
        assert_eq!(
            wide("crcbl"),
            Some(vec![0x0063, 0x0072, 0x0063, 0x0062, 0x006C, 0])
        );
        assert_eq!(wide(""), Some(vec![0]));
        // Non-BMP characters become surrogate pairs, which is what UTF-16 is.
        assert_eq!(wide("🎮").map(|text| text.len()), Some(3));
        assert_eq!(wide("save\0nothing"), None);
    }

    #[test]
    fn the_overlapped_window_style_is_the_sum_of_its_parts() {
        // The literal in `winuser.h` is 0x00CF0000, and spelling it as a union
        // of named bits is only correct if it comes to the same number.
        assert_eq!(style::OVERLAPPED_WINDOW, 0x00CF_0000);
        assert_eq!(style::CAPTION, 0x00C0_0000);
        assert_eq!(value::CS_REDRAW, 0x0003);
    }

    #[test]
    fn the_transparency_values_are_the_sdks() {
        // `winuser.h` and `dwmapi.h`. A wrong one is an extended style or an
        // attribute the system ignores, and no call fails to say so.
        assert_eq!(style::EX_NO_REDIRECTION_BITMAP, 0x0020_0000);
        assert_eq!(dwm::WINDOW_CORNER_PREFERENCE, 33);
        assert_eq!(dwm::CORNER_DEFAULT, 0);
        assert_eq!(dwm::CORNER_DO_NOT_ROUND, 1);
        assert_eq!(dwm::BORDER_COLOR, 34);
        assert_eq!(dwm::COLOR_DEFAULT, 0xFFFF_FFFF);
        assert_eq!(dwm::COLOR_NONE, 0xFFFF_FFFE);
        // `wingdi.h`; a wrong mode intersects or subtracts instead.
        assert_eq!(value::RGN_OR, 2);
        assert_eq!(value::REGION_ERROR, 0);
    }

    /// The conversion from `QueryDisplayConfig`'s rational to millihertz, and
    /// the target-mode index extraction. These are the two pure pieces of the
    /// exact-refresh path; `win32::monitors` (Windows-only) only wires them.
    #[test]
    fn a_rational_and_a_mode_index_convert_exactly() {
        // 59.94 Hz — the mode `EnumDisplaySettingsW` reports as the integer 60.
        let ntsc = DisplayConfigRational {
            numerator: 60_000,
            denominator: 1_001,
        };
        assert_eq!(ntsc.millihertz(0), Some(59_940));
        // 60.00 Hz stays exact.
        let sixty = DisplayConfigRational {
            numerator: 60_000,
            denominator: 1_000,
        };
        assert_eq!(sixty.millihertz(0), Some(60_000));
        // A divider halves the rate (interlaced modes), per the structure's
        // `vSyncFreqDivider` contract.
        assert_eq!(sixty.millihertz(2), Some(30_000));
        // Degenerate rationals are "no rate", not zero hertz.
        assert_eq!(DisplayConfigRational::default().millihertz(0), None);
        assert_eq!(
            DisplayConfigRational {
                numerator: 1,
                denominator: 0
            }
            .millihertz(0),
            None
        );

        // The target-mode index is the high 16 bits; 0xffff there is "no mode".
        let with_mode = DisplayConfigPathTargetInfo {
            mode_info_idx: 0x0003_0005, // target mode 3, desktop mode 5
            ..Default::default()
        };
        assert_eq!(with_mode.target_mode_index(), Some(3));
        let without = DisplayConfigPathTargetInfo {
            mode_info_idx: 0xFFFF_0000, // target half is the invalid sentinel
            ..Default::default()
        };
        assert_eq!(without.target_mode_index(), None);
    }
}

#[cfg(all(test, target_os = "windows"))]
mod sdk_layout;