Cursors: paint the tool cursors on Wayland, where the compositor showed the bitmap twice too big (fixes #1645)

apps/vectorcraft/src/main.rs

@@ -489,6 +489,8 @@ fn start_pick(request: PickRequest, parent: &Parent, ui: &egui::Context) -> Opti
 
 /// The host's services; `ui` is woken when a file dialog answers.
 fn services(parent: Parent, ui: egui::Context) -> Services {
+    use winit::raw_window_handle::{HasWindowHandle as _, RawWindowHandle};
+    let wayland = parent.as_ref().and_then(|w| w.window_handle().ok()).is_some_and(|h| matches!(h.as_raw(), RawWindowHandle::Wayland(_)));
     let (p1, p2, p3, p4, p5) = (parent.clone(), parent.clone(), parent.clone(), parent.clone(), parent);
     Services {
         pick_open: Some(Box::new(move |pick: &FilePick| pick_now(PickRequest::Open(pick.clone()), &p1).into_iter().next())),
@@ -498,6 +500,7 @@ fn services(parent: Parent, ui: egui::Context) -> Services {
         // dialogs run the window's events while they are open.
         start_pick: cfg!(unix).then(|| Box::new(move |request: PickRequest| start_pick(request, &p5, &ui)) as vectorcraft_ui_egui::picks::StartPick),
         dialogs_are_sheets: cfg!(target_os = "macos"),
+        wayland,
         read: Some(Box::new(|p: &str| std::fs::read(p).map_err(|e| e.to_string()))),
         write: Some(Box::new(write_file)),
         // Background Save and Export write from a worker thread.

crates/ui-egui/src/canvas.rs

@@ -492,7 +492,7 @@ pub fn show(app: &mut VectorcraftApp, ui: &mut Ui) {
             match ui.input(|i| i.pointer.hover_pos()) {
                 // An OS cursor: the system moves it at once, where a painted one trails the pointer
                 // (#444). The system cursor stands in for cursors without a glyph.
-                Some(_) if custom && crate::cursors::OS_CURSORS => {
+                Some(_) if custom && crate::cursors::os_cursors(crate::cursors::OS_CURSORS, app.services.wayland) => {
                     let ppp = ui.ctx().pixels_per_point() / ui_scale;
                     ui.ctx().set_cursor_image(app.canvas.cursors.get(c, ppp));
                     cursor_icon(c)

crates/ui-egui/src/cursors.rs

@@ -386,6 +386,14 @@ pub fn paint(painter: &Painter, c: Cursor, p: Pos2, scale: f32) -> bool {
 /// bitmap cursors there): those paint them into the window ([`paint`]).
 pub const OS_CURSORS: bool = !cfg!(any(target_os = "macos", target_arch = "wasm32"));
 
+/// Does this window show the glyphs as OS cursors, on a build that can ([`OS_CURSORS`])? Not on
+/// Wayland, where the compositor decides how big a cursor bitmap shows: Hyprland shows each pixel
+/// as a point, twice too big on a 2× display (#1645). The window paints them there, as PhotoCraft
+/// and PdfCraft do.
+pub fn os_cursors(build: bool, wayland: bool) -> bool {
+    build && !wayland
+}
+
 /// The cursor bitmaps handed to the OS, by (cursor, pixels per point): each glyph is rasterized
 /// once, and handing the same `Arc` every frame keeps the window's OS cursor instead of making a
 /// new one.
@@ -655,6 +663,21 @@ mod tests {
         assert!(off.platform_output.cursor_image.is_none());
     }
 
+    /// On Wayland the glyph is painted and the pointer hidden over the canvas, on every build (#1645).
+    #[test]
+    fn a_wayland_window_paints_the_tool_cursor() {
+        let mut app = VectorcraftApp::new(Session::new(), crate::Services { wayland: true, ..Default::default() });
+        app.run("file.new", json!({"width": 400, "height": 300})).unwrap();
+        let ctx = egui::Context::default();
+        for _ in 0..3 {
+            frame(&mut app, &ctx, vec![]);
+        }
+        let over = app.canvas_rect.unwrap().center();
+        let out = frame(&mut app, &ctx, vec![egui::Event::PointerMoved(over)]);
+        assert!(out.platform_output.cursor_image.is_none());
+        assert_eq!(out.platform_output.cursor_icon, egui::CursorIcon::None);
+    }
+
     /// User Interface › Scale Cursor Proportional to UI (#394): off, the tool cursors keep their
     /// size whatever the UI Scaling; on, they grow with it.
     #[test]
@@ -692,6 +715,13 @@ mod tests {
         assert!(full.contains(pos2(100.0, 100.0)) && half.contains(pos2(100.0, 100.0)), "{full:?} {half:?}");
     }
 
+    #[test]
+    fn wayland_windows_paint_the_glyphs() {
+        assert!(os_cursors(true, false), "Windows, X11");
+        assert!(!os_cursors(true, true), "Wayland: the compositor would size the bitmap (#1645)");
+        assert!(!os_cursors(false, false) && !os_cursors(false, true), "macOS, the web");
+    }
+
     #[test]
     fn arrow_hotspot_is_tip() {
         let pts = arrow_points(pos2(10.0, 20.0));

crates/ui-egui/src/lib.rs

@@ -261,6 +261,9 @@ pub struct Services {
     /// [`Self::start_pick`]'s dialogs are sheets on the window (macOS): while one is open the app
     /// neither quits nor closes documents, as under the modal dialog before.
     pub dialogs_are_sheets: bool,
+    /// The window is on Wayland: the tool cursors are painted into it instead of handed to the
+    /// compositor as bitmaps ([`cursors::os_cursors`]).
+    pub wayland: bool,
 }
 
 /// Cached canvas raster.