retroglyph-window 0.5.0

//! wasm32-only DPR-capping, browser-viewport-fill, and pointer-rescaling helpers used by `super::run`
//! on `wasm32`.

#[cfg(target_arch = "wasm32")]
use std::sync::Arc;
#[cfg(target_arch = "wasm32")]
use winit::window::Window;

/// Upper bound on the device pixel ratio used to size the canvas backing store. Present cost is
/// O(pixels), so an uncapped DPR (3 on many phones, 2 on most laptops) quadruples or worse the
/// per-frame rasterize/present work for marginal crispness on a pseudo-graphic UI.
#[cfg(target_arch = "wasm32")]
const MAX_DEVICE_PIXEL_RATIO: f64 = 1.5;

/// The browser viewport's CSS width/height, or `None` if running outside a browser `window`
/// context. Shared by the two physical-size helpers below.
#[cfg(target_arch = "wasm32")]
fn web_viewport_css_size() -> Option<(f64, f64)> {
    let window = web_sys::window()?;
    let width = window.inner_width().ok()?.as_f64()?;
    let height = window.inner_height().ok()?.as_f64()?;
    Some((width, height))
}

/// The browser viewport size in true physical (device) pixels: i.e. at the real, uncapped
/// `devicePixelRatio`.
///
/// Pass this to winit's `with_inner_size`/`request_inner_size` (and *only* this, never
/// [`web_viewport_surface_physical_size`]). winit's wasm backend always converts the
/// `PhysicalSize` it's given back to a logical (CSS pixel) size by dividing by the real
/// `devicePixelRatio` to set the canvas's inline style; handing it anything scaled by a
/// different ratio (like our DPR-capped surface size) makes the canvas's CSS size come out
/// smaller than the viewport.
#[cfg(target_arch = "wasm32")]
#[allow(clippy::cast_possible_truncation, clippy::cast_sign_loss)]
pub(super) fn web_viewport_layout_physical_size() -> Option<winit::dpi::PhysicalSize<u32>> {
    let (width, height) = web_viewport_css_size()?;
    let dpr = web_sys::window()?.device_pixel_ratio();
    Some(winit::dpi::PhysicalSize::new(
        (width * dpr).round() as u32,
        (height * dpr).round() as u32,
    ))
}

/// Ratio to convert a pointer position winit reports (always in *real*, uncapped-DPR physical
/// pixels: see `to_physical(super::scale_factor)` in `winit`'s wasm `pointer.rs`) into the
/// raster-backing-store pixel space that
/// [`Presenter::cell_size`](crate::presenter::Presenter::cell_size), and therefore
/// [`translate_pixel_to_cell`](super::translate::translate_pixel_to_cell), are expressed in.
///
/// `1.0` whenever `real_dpr` is already at or below `capped_dpr` (desktop, non-Retina): no
/// correction needed. Below that, taps/clicks land scaled past their true position --
/// south-east of the intended cell, growing with how far `real_dpr` exceeds the cap (2x at DPR
/// 3 against a 1.5 cap). Pure math, kept separate from [`wasm_pointer_scale`] so it's
/// unit-testable without a wasm window (hence `cfg(any(.., test))`: unused on a native non-test
/// build, whose `on_cursor_moved` hardcodes `scale = 1.0` instead of calling this).
#[cfg(any(target_arch = "wasm32", test))]
fn dpr_pointer_scale(real_dpr: f64, capped_dpr: f64) -> f64 {
    (capped_dpr / real_dpr).min(1.0)
}

/// [`dpr_pointer_scale`] using the page's actual `devicePixelRatio` and [`MAX_DEVICE_PIXEL_RATIO`].
/// `1.0` if no browser `window` is available.
#[cfg(target_arch = "wasm32")]
pub(super) fn wasm_pointer_scale() -> f64 {
    web_sys::window().map_or(1.0, |w| {
        dpr_pointer_scale(w.device_pixel_ratio(), MAX_DEVICE_PIXEL_RATIO)
    })
}

/// The physical pixel size of the software renderer's raster backing store, capped at
/// [`MAX_DEVICE_PIXEL_RATIO`] for `present()` cost.
///
/// Not the size passed to winit (see [`web_viewport_layout_physical_size`]):
/// winit's `Resized` event always reports back whatever physical size we last requested, so if
/// this capped size were also used for `request_inner_size`, the canvas's CSS size would shrink
/// below the viewport on any device whose real DPR exceeds the cap (i.e. almost every phone).
#[cfg(target_arch = "wasm32")]
#[allow(clippy::cast_possible_truncation, clippy::cast_sign_loss)]
pub(super) fn web_viewport_surface_physical_size() -> Option<winit::dpi::PhysicalSize<u32>> {
    let (width, height) = web_viewport_css_size()?;
    let dpr = web_sys::window()?
        .device_pixel_ratio()
        .min(MAX_DEVICE_PIXEL_RATIO);
    Some(winit::dpi::PhysicalSize::new(
        (width * dpr).round() as u32,
        (height * dpr).round() as u32,
    ))
}

/// Re-requests the window's inner size to match the browser viewport on every `resize` event, so
/// the canvas keeps filling the screen instead of staying pinned to its size at first paint.
#[cfg(target_arch = "wasm32")]
pub(super) fn install_viewport_resize_listener(window: &Arc<Window>) {
    use wasm_bindgen::JsCast;
    use wasm_bindgen::prelude::Closure;

    let Some(web_window) = web_sys::window() else {
        return;
    };
    let window = window.clone();
    let closure = Closure::<dyn FnMut()>::new(move || {
        // Only the uncapped layout size goes to winit; `on_resized` (fired
        // by the `Resized` event this triggers) independently recomputes
        // the DPR-capped surface size for the backing store.
        if let Some(size) = web_viewport_layout_physical_size() {
            let _ = window.request_inner_size(size);
        }
    });
    if web_window
        .add_event_listener_with_callback("resize", closure.as_ref().unchecked_ref())
        .is_ok()
    {
        // Leaked: the listener, and the closure it wraps, need
        // to live as long as the page does: there's no window-teardown
        // hook on wasm to drop it from.
        closure.forget();
    }
}

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

    // ── dpr_pointer_scale ─────────────────────────────────────────────────────

    #[test]
    fn dpr_pointer_scale_no_correction_below_cap() {
        // Real DPR at or below the cap: pointer positions already match the
        // (uncapped) backing store, no rescale needed.
        assert!((dpr_pointer_scale(1.0, 1.5) - 1.0).abs() < 1e-9);
        assert!((dpr_pointer_scale(1.5, 1.5) - 1.0).abs() < 1e-9);
    }

    #[test]
    fn dpr_pointer_scale_corrects_above_cap() {
        // Real DPR 3 against a 1.5 cap: the backing store is half the real
        // resolution, so pointer positions must be halved to land on the
        // right cell instead of drifting south-east of it.
        assert!((dpr_pointer_scale(3.0, 1.5) - 0.5).abs() < 1e-9);
        assert!((dpr_pointer_scale(2.0, 1.5) - 0.75).abs() < 1e-9);
    }
}