feat: render named cursor images

compositor/src/cursor.rs

@@ -0,0 +1,146 @@
+use std::{fs, sync::OnceLock};
+
+use smithay::{
+    backend::{allocator::Fourcc, renderer::element::memory::MemoryRenderBuffer},
+    input::pointer::CursorIcon,
+    utils::{Buffer, Point, Size, Transform},
+};
+use xcursor::{CursorTheme, parser::Image};
+
+const DEFAULT_CURSOR_SIZE: u32 = 24;
+
+#[derive(Debug, Clone)]
+pub(crate) struct NamedCursor {
+    pub buffer: MemoryRenderBuffer,
+    pub hotspot: Point<i32, Buffer>,
+}
+
+pub(crate) fn cursor_theme() -> CursorTheme {
+    let name = std::env::var("XCURSOR_THEME").unwrap_or_else(|_| "default".into());
+
+    CursorTheme::load(&name)
+}
+
+pub(crate) fn load_named_cursor(theme: &CursorTheme, icon: CursorIcon) -> NamedCursor {
+    let requested_size = cursor_size();
+    let image = cursor_names(icon)
+        .iter()
+        .find_map(|name| load_image(theme, name, requested_size));
+
+    match image {
+        Some(image) => cursor_from_image(image),
+        None => fallback_cursor(),
+    }
+}
+
+fn cursor_size() -> u32 {
+    static SIZE: OnceLock<u32> = OnceLock::new();
+
+    *SIZE.get_or_init(|| {
+        std::env::var("XCURSOR_SIZE")
+            .ok()
+            .and_then(|value| value.parse().ok())
+            .filter(|size| *size > 0)
+            .unwrap_or(DEFAULT_CURSOR_SIZE)
+    })
+}
+
+fn cursor_names(icon: CursorIcon) -> [&'static str; 3] {
+    match icon {
+        CursorIcon::Default => ["default", "left_ptr", "arrow"],
+        CursorIcon::Pointer => ["pointer", "hand2", "left_ptr"],
+        CursorIcon::Text => ["text", "xterm", "left_ptr"],
+        _ => [icon.name(), "default", "left_ptr"],
+    }
+}
+
+fn load_image(theme: &CursorTheme, name: &str, requested_size: u32) -> Option<Image> {
+    let path = theme.load_icon(name)?;
+    let bytes = fs::read(path).ok()?;
+
+    xcursor::parser::parse_xcursor(&bytes)?
+        .into_iter()
+        .min_by_key(|image| {
+            (
+                image.size.abs_diff(requested_size),
+                image.width.abs_diff(requested_size),
+            )
+        })
+}
+
+fn cursor_from_image(image: Image) -> NamedCursor {
+    let size = Size::<i32, Buffer>::from((image.width as i32, image.height as i32));
+    let buffer = MemoryRenderBuffer::from_slice(
+        &image.pixels_rgba,
+        Fourcc::Abgr8888,
+        size,
+        1,
+        Transform::Normal,
+        None,
+    );
+
+    NamedCursor {
+        buffer,
+        hotspot: Point::from((image.xhot as i32, image.yhot as i32)),
+    }
+}
+
+fn fallback_cursor() -> NamedCursor {
+    const WIDTH: usize = 12;
+    const HEIGHT: usize = 18;
+    let mut pixels = vec![0_u8; WIDTH * HEIGHT * 4];
+
+    for y in 0..HEIGHT {
+        let body_width = (y / 2 + 1).min(8);
+
+        for x in 0..body_width {
+            let edge = x == 0 || x + 1 == body_width || y == 0;
+            let offset = (y * WIDTH + x) * 4;
+            let color = if edge { 0 } else { 255 };
+            pixels[offset..offset + 4].copy_from_slice(&[color, color, color, 255]);
+        }
+    }
+
+    NamedCursor {
+        buffer: MemoryRenderBuffer::from_slice(
+            &pixels,
+            Fourcc::Abgr8888,
+            Size::<i32, Buffer>::from((WIDTH as i32, HEIGHT as i32)),
+            1,
+            Transform::Normal,
+            None,
+        ),
+        hotspot: Point::default(),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use smithay::input::pointer::CursorIcon;
+
+    use super::cursor_names;
+
+    #[test]
+    fn supplies_legacy_fallback_names_for_common_cursors() {
+        assert_eq!(
+            cursor_names(CursorIcon::Default),
+            ["default", "left_ptr", "arrow"]
+        );
+        assert_eq!(
+            cursor_names(CursorIcon::Pointer),
+            ["pointer", "hand2", "left_ptr"]
+        );
+        assert_eq!(
+            cursor_names(CursorIcon::Text),
+            ["text", "xterm", "left_ptr"]
+        );
+    }
+
+    #[test]
+    fn falls_back_to_default_for_other_named_cursors() {
+        assert_eq!(
+            cursor_names(CursorIcon::Crosshair),
+            ["crosshair", "default", "left_ptr"]
+        );
+    }
+}