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//! How big a custom cursor image has to be when it reaches the platform, so it
//! appears the size [`CustomCursorSize`] asks for everywhere.
//!
//! Platforms disagree about two things. macOS takes an image's pixels as
//! points and enlarges them by the display density and by the person's
//! pointer size itself. Windows, X11 and Wayland take them as physical pixels
//! and enlarge them by neither. Each backend states what its platform does in
//! a [`CursorSurface`], and [`image_scale`] says what is left for the app to do.
use crate::CustomCursorSize;
/// What the platform under a window does to a custom cursor image by itself.
#[derive(Clone, Copy, Debug, PartialEq)]
pub(crate) struct CursorSurface {
/// How much the person has enlarged the system pointer; 1 when they have
/// not.
pub(crate) pointer_scale: f64,
/// The window's physical pixels per logical point.
pub(crate) density: f64,
/// The platform reads an image's pixels as points and enlarges them by
/// the density itself.
pub(crate) image_in_points: bool,
/// The platform enlarges a custom image by the pointer scale itself.
pub(crate) enlarges_custom_images: bool,
}
/// A factor to scale by: 1 for anything missing, below 1 or not a number.
pub(crate) fn usable_scale(raw: f64) -> f64 {
if raw.is_finite() && raw > 1.0 {
raw
} else {
1.0
}
}
fn usable_density(raw: f64) -> f64 {
if raw.is_finite() && raw > 0.0 {
raw
} else {
1.0
}
}
/// How much a custom cursor image drawn one pixel to a point has to be scaled
/// before it reaches `surface`, for it to appear the size `size` asks for: the
/// drawn size in points, enlarged by the pointer scale when it follows the
/// system. 1 hands it over as drawn.
pub(crate) fn image_scale(size: CustomCursorSize, surface: CursorSurface) -> f64 {
let pointer = usable_scale(surface.pointer_scale);
let density = usable_density(surface.density);
let wanted = density
* match size {
CustomCursorSize::FollowSystem => pointer,
CustomCursorSize::AsDrawn => 1.0,
};
let given = if surface.image_in_points {
density
} else {
1.0
} * if surface.enlarges_custom_images {
pointer
} else {
1.0
};
wanted / given
}
/// Whether `factor` changes the image at all.
pub(crate) fn rescales(factor: f64) -> bool {
(factor - 1.0).abs() > 1e-3
}
/// The pointer scale an X11 or Wayland session asks for: its `XCURSOR_SIZE`
/// over the 24 pixels cursor themes are drawn at, the size winit's own themed
/// cursors take.
#[cfg(any(test, not(any(target_os = "macos", target_os = "windows"))))]
pub(crate) fn xcursor_scale(xcursor_size: Option<&str>) -> f64 {
xcursor_size
.and_then(|size| size.trim().parse::<f64>().ok())
.map_or(1.0, |size| usable_scale(size / 24.0))
}
/// The pointer scale Windows asks for: its `CursorBaseSize` over the 32
/// pixels of the standard cursors.
#[cfg(any(test, target_os = "windows"))]
pub(crate) fn windows_cursor_scale(cursor_base_size: Option<u32>) -> f64 {
cursor_base_size.map_or(1.0, |size| usable_scale(f64::from(size) / 32.0))
}
/// `pixels`, RGBA `width` by `height`, scaled by `factor` nearest-neighbour,
/// so a cursor drawn as pixel art keeps hard pixel edges, with its `hotspot`
/// moved to the same place on the scaled image.
pub(crate) fn scaled_image(
pixels: &[u8],
width: u32,
height: u32,
hotspot: (u32, u32),
factor: f64,
) -> (Vec<u8>, u32, u32, (u32, u32)) {
let scale = |length: u32| ((f64::from(length) * factor).round() as u32).max(1);
let (scaled_width, scaled_height) = (scale(width), scale(height));
let source = |at: u32, length: u32| {
(((f64::from(at) + 0.5) / factor) as u32).min(length.saturating_sub(1))
};
let mut scaled = Vec::with_capacity(scaled_width as usize * scaled_height as usize * 4);
for y in 0..scaled_height {
let row = source(y, height) as usize * width as usize;
for x in 0..scaled_width {
let at = (row + source(x, width) as usize) * 4;
scaled.extend_from_slice(&pixels[at..at + 4]);
}
}
let place =
|at: u32, length: u32| ((f64::from(at) * factor) as u32).min(length.saturating_sub(1));
let hotspot = (
place(hotspot.0, scaled_width),
place(hotspot.1, scaled_height),
);
(scaled, scaled_width, scaled_height, hotspot)
}
#[cfg(test)]
#[path = "tests/cursor_scale_tests.rs"]
mod tests;