crcbl-input 0.17.2

//! Hand-written FFI to XInput: the structures `XInputGetState` fills, and
//! the ones the undocumented `XInputGetCapabilitiesEx` fills.
//!
//! **Loaded at runtime, not linked** — the opposite of the Win32 shell's
//! `#[link]` decision, for the reason that module's docs give for when the
//! opposite would be right: a library that can be absent. `xinput1_4.dll` ships
//! with Windows 8 and later, but a stripped Windows (Server Core, some N and
//! container images) can lack it, and a `#[link]` would stop the process in the
//! loader before a game could fall back to keyboard and mouse.
//! `xinput9_1_0.dll` is the older redistributable name, tried second.

#![allow(non_snake_case)]

/// `XINPUT_GAMEPAD`.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub(crate) struct XInputGamepad {
    /// `wButtons`: a bitmask of the `XINPUT_GAMEPAD_*` button constants.
    pub(crate) buttons: u16,
    /// `bLeftTrigger`: 0 at rest, 255 fully pulled.
    pub(crate) left_trigger: u8,
    /// `bRightTrigger`.
    pub(crate) right_trigger: u8,
    /// `sThumbLX`: −32768…32767, positive right.
    pub(crate) thumb_lx: i16,
    /// `sThumbLY`: −32768…32767, **positive up** — already the seam's sign.
    pub(crate) thumb_ly: i16,
    /// `sThumbRX`.
    pub(crate) thumb_rx: i16,
    /// `sThumbRY`, positive up.
    pub(crate) thumb_ry: i16,
}

/// `XINPUT_STATE`.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub(crate) struct XInputState {
    /// `dwPacketNumber`: changes whenever the state does. Not read: the poller
    /// compares mapped snapshots, which is the same answer without trusting a
    /// counter the backend cannot test.
    pub(crate) packet_number: u32,
    /// `Gamepad`.
    pub(crate) gamepad: XInputGamepad,
}

/// `XINPUT_VIBRATION`. Only here as part of [`XInputCapabilities`].
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub(crate) struct XInputVibration {
    /// `wLeftMotorSpeed`.
    pub(crate) left_motor: u16,
    /// `wRightMotorSpeed`.
    pub(crate) right_motor: u16,
}

/// `XINPUT_CAPABILITIES`. Only here as the head of
/// [`XInputCapabilitiesEx`]; none of it is read.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub(crate) struct XInputCapabilities {
    /// `Type`.
    pub(crate) kind: u8,
    /// `SubType`.
    pub(crate) sub_type: u8,
    /// `Flags`.
    pub(crate) flags: u16,
    /// `Gamepad`.
    pub(crate) gamepad: XInputGamepad,
    /// `Vibration`.
    pub(crate) vibration: XInputVibration,
}

/// What `xinput1_4.dll`'s **undocumented** export ordinal 108
/// (`XInputGetCapabilitiesEx`) fills: the documented `XINPUT_CAPABILITIES`,
/// then the device's USB vendor and product ids, which nothing documented in
/// XInput exposes.
///
/// No Windows SDK header declares it. The layout is SDL's declaration
/// (`SDL_XINPUT_CAPABILITIES_EX` in SDL's `src/core/windows/SDL_xinput.h`),
/// which SDL has read vendor ids through for years — including to recognise
/// Steam's virtual pad, which is what this backend reads it for.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub(crate) struct XInputCapabilitiesEx {
    /// `Capabilities`.
    pub(crate) capabilities: XInputCapabilities,
    /// `VendorId`: the USB vendor id.
    pub(crate) vendor_id: u16,
    /// `ProductId`.
    pub(crate) product_id: u16,
    /// `ProductVersion`.
    pub(crate) product_version: u16,
    /// Unnamed in SDL's declaration.
    pub(crate) unknown1: u16,
    /// Unnamed in SDL's declaration.
    pub(crate) unknown2: u32,
}

/// The export ordinal of `XInputGetCapabilitiesEx` in `xinput1_4.dll`
/// (SDL's `SDL_xinput.c` resolves it the same way). `xinput9_1_0.dll` does
/// not export it.
#[cfg(windows)]
pub(crate) const GET_CAPABILITIES_EX_ORDINAL: usize = 108;

/// `XInputGetCapabilitiesEx(DWORD dwReserved, DWORD dwUserIndex, DWORD
/// dwFlags, XINPUT_CAPABILITIES_EX *pCapabilities) -> DWORD`, as SDL declares
/// it; SDL passes `1` for the reserved argument and `0` for the flags, and so
/// does this backend.
#[cfg(windows)]
pub(crate) type XInputGetCapabilitiesExFn =
    unsafe extern "system" fn(u32, u32, u32, *mut XInputCapabilitiesEx) -> u32;

/// `XUSER_MAX_COUNT`: XInput's user slots, 0 through 3.
pub(crate) const XUSER_MAX_COUNT: u32 = 4;

/// `ERROR_SUCCESS`: the slot has a controller, and the state is filled in.
#[cfg(windows)]
pub(crate) const ERROR_SUCCESS: u32 = 0;
/// `ERROR_DEVICE_NOT_CONNECTED`: the slot is empty. Not a failure.
pub(crate) const ERROR_DEVICE_NOT_CONNECTED: u32 = 1167;

// The `XINPUT_GAMEPAD_*` button bits. 0x0400 is the Guide button, which only
// the undocumented ordinal-100 `XInputGetStateEx` reports; `XInputGetState`
// never sets it, so it is not declared.
pub(crate) const XINPUT_GAMEPAD_DPAD_UP: u16 = 0x0001;
pub(crate) const XINPUT_GAMEPAD_DPAD_DOWN: u16 = 0x0002;
pub(crate) const XINPUT_GAMEPAD_DPAD_LEFT: u16 = 0x0004;
pub(crate) const XINPUT_GAMEPAD_DPAD_RIGHT: u16 = 0x0008;
pub(crate) const XINPUT_GAMEPAD_START: u16 = 0x0010;
pub(crate) const XINPUT_GAMEPAD_BACK: u16 = 0x0020;
pub(crate) const XINPUT_GAMEPAD_LEFT_THUMB: u16 = 0x0040;
pub(crate) const XINPUT_GAMEPAD_RIGHT_THUMB: u16 = 0x0080;
pub(crate) const XINPUT_GAMEPAD_LEFT_SHOULDER: u16 = 0x0100;
pub(crate) const XINPUT_GAMEPAD_RIGHT_SHOULDER: u16 = 0x0200;
pub(crate) const XINPUT_GAMEPAD_A: u16 = 0x1000;
pub(crate) const XINPUT_GAMEPAD_B: u16 = 0x2000;
pub(crate) const XINPUT_GAMEPAD_X: u16 = 0x4000;
pub(crate) const XINPUT_GAMEPAD_Y: u16 = 0x8000;

/// `XInputGetState(DWORD dwUserIndex, XINPUT_STATE *pState) -> DWORD`.
#[cfg(windows)]
pub(crate) type XInputGetStateFn = unsafe extern "system" fn(u32, *mut XInputState) -> u32;

/// `HMODULE`.
#[cfg(windows)]
pub(crate) type Module = *mut core::ffi::c_void;

// The loader half of `kernel32`: all this backend needs to find XInput.
#[cfg(windows)]
#[link(name = "kernel32")]
unsafe extern "system" {
    pub(crate) fn LoadLibraryW(name: *const u16) -> Module;
    pub(crate) fn GetProcAddress(module: Module, name: *const u8) -> *mut core::ffi::c_void;
    pub(crate) fn FreeLibrary(module: Module) -> i32;
    pub(crate) fn GetLastError() -> u32;
}

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

    /// The layouts against `Xinput.h`. Every number is the SDK's own
    /// `sizeof`/`offsetof`, printed by a C program built with MSVC 19.44
    /// (`_MSC_FULL_VER` 194435229) against Windows SDK 10.0.26100.0 for x64 —
    /// the same toolchain the Win32 shell's table was printed with. Every field
    /// is fixed-width, so these hold on every target the tests run on, not only
    /// Windows.
    #[test]
    fn the_structures_match_the_c_layout() {
        assert_layout!(XInputGamepad, 12, {
            buttons: 0, 2;
            left_trigger: 2, 1;
            right_trigger: 3, 1;
            thumb_lx: 4, 2;
            thumb_ly: 6, 2;
            thumb_rx: 8, 2;
            thumb_ry: 10, 2;
        });
        assert_layout!(XInputState, 16, {
            packet_number: 0, 4;
            gamepad: 4, 12;
        });
    }

    /// The structures behind ordinal 108. Every number is MinGW-w64 GCC
    /// 16.2.0's `sizeof`/`offsetof` for x64, printed by a C++ program built
    /// against MinGW's own `xinput.h` — for `XINPUT_CAPABILITIES_EX`, which no
    /// SDK header declares, against SDL's declaration of it. As above, every
    /// field is fixed-width, so the numbers hold on every target.
    #[test]
    fn the_capabilities_structures_match_the_c_layout() {
        assert_layout!(XInputVibration, 4, {
            left_motor: 0, 2;
            right_motor: 2, 2;
        });
        assert_layout!(XInputCapabilities, 20, {
            kind: 0, 1;
            sub_type: 1, 1;
            flags: 2, 2;
            gamepad: 4, 12;
            vibration: 16, 4;
        });
        assert_layout!(XInputCapabilitiesEx, 32, {
            capabilities: 0, 20;
            vendor_id: 20, 2;
            product_id: 22, 2;
            product_version: 24, 2;
            unknown1: 26, 2;
            unknown2: 28, 4;
        });
    }
}