wayland: support fractional scale for custom cursor

src/changelog/unreleased.md

@@ -253,3 +253,4 @@ changelog entry.
 - On macOS, fixed `run_app_on_demand` returning without closing open windows.
 - On Wayland, fixed a crash when consequently calling `set_cursor_grab` without pointer focus.
 - On Wayland, ensure that external event loop is woken-up when using pump_events and integrating via `FD`.
+- On Wayland, apply fractional scaling to custom cursors.

src/platform_impl/linux/wayland/seat/mod.rs

@@ -96,8 +96,12 @@ impl SeatHandler for WinitState {
             },
             SeatCapability::Pointer if seat_state.pointer.is_none() => {
                 let surface = self.compositor_state.create_surface(queue_handle);
+                let viewport = self
+                    .viewporter_state
+                    .as_ref()
+                    .map(|state| state.get_viewport(&surface, queue_handle));
                 let surface_id = surface.id();
-                let pointer_data = WinitPointerData::new(seat.clone());
+                let pointer_data = WinitPointerData::new(seat.clone(), viewport);
                 let themed_pointer = self
                     .seat_state
                     .get_pointer_with_theme_and_data(

src/platform_impl/linux/wayland/seat/pointer/mod.rs

@@ -18,6 +18,7 @@ use sctk::reexports::protocols::wp::cursor_shape::v1::client::wp_cursor_shape_ma
 use sctk::reexports::protocols::wp::pointer_constraints::zv1::client::zwp_pointer_constraints_v1::{Lifetime, ZwpPointerConstraintsV1};
 use sctk::reexports::client::globals::{BindError, GlobalList};
 use sctk::reexports::csd_frame::FrameClick;
+use sctk::reexports::protocols::wp::viewporter::client::wp_viewport::WpViewport;
 
 use sctk::compositor::SurfaceData;
 use sctk::globals::GlobalData;
@@ -246,13 +247,17 @@ pub struct WinitPointerData {
 
     /// The data required by the sctk.
     sctk_data: PointerData,
+
+    /// Viewport for fractional cursor.
+    viewport: Option<WpViewport>,
 }
 
 impl WinitPointerData {
-    pub fn new(seat: WlSeat) -> Self {
+    pub fn new(seat: WlSeat, viewport: Option<WpViewport>) -> Self {
         Self {
             inner: Mutex::new(WinitPointerDataInner::default()),
             sctk_data: PointerData::new(seat),
+            viewport,
         }
     }
 
@@ -333,6 +338,18 @@ impl WinitPointerData {
             locked_pointer.set_cursor_position_hint(surface_x, surface_y);
         }
     }
+
+    pub fn viewport(&self) -> Option<&WpViewport> {
+        self.viewport.as_ref()
+    }
+}
+
+impl Drop for WinitPointerData {
+    fn drop(&mut self) {
+        if let Some(viewport) = self.viewport.take() {
+            viewport.destroy();
+        }
+    }
 }
 
 impl PointerDataExt for WinitPointerData {

src/platform_impl/linux/wayland/window/state.rs

@@ -29,7 +29,7 @@ use tracing::{info, warn};
 use wayland_protocols_plasma::blur::client::org_kde_kwin_blur::OrgKdeKwinBlur;
 
 use crate::cursor::CustomCursor as CoreCustomCursor;
-use crate::dpi::{LogicalPosition, LogicalSize, PhysicalSize, Size};
+use crate::dpi::{LogicalPosition, LogicalSize, PhysicalPosition, PhysicalSize, Size};
 use crate::error::{NotSupportedError, RequestError};
 use crate::platform_impl::wayland::event_loop::OwnedDisplayHandle;
 use crate::platform_impl::wayland::logical_to_physical_rounded;
@@ -725,17 +725,26 @@ impl WindowState {
     }
 
     fn apply_custom_cursor(&self, cursor: &CustomCursor) {
-        self.apply_on_pointer(|pointer, _| {
+        self.apply_on_pointer(|pointer, data| {
             let surface = pointer.surface();
 
-            let scale = surface.data::<SurfaceData>().unwrap().surface_data().scale_factor();
+            let scale = if let Some(viewport) = data.viewport() {
+                let scale = self.scale_factor();
+                let size = PhysicalSize::new(cursor.w, cursor.h).to_logical(scale);
+                viewport.set_destination(size.width, size.height);
+                scale
+            } else {
+                let scale = surface.data::<SurfaceData>().unwrap().surface_data().scale_factor();
+                surface.set_buffer_scale(scale);
+                scale as f64
+            };
 
-            surface.set_buffer_scale(scale);
             surface.attach(Some(cursor.buffer.wl_buffer()), 0, 0);
             if surface.version() >= 4 {
                 surface.damage_buffer(0, 0, cursor.w, cursor.h);
             } else {
-                surface.damage(0, 0, cursor.w / scale, cursor.h / scale);
+                let size = PhysicalSize::new(cursor.w, cursor.h).to_logical(scale);
+                surface.damage(0, 0, size.width, size.height);
             }
             surface.commit();
 
@@ -745,12 +754,9 @@ impl WindowState {
                 .and_then(|data| data.pointer_data().latest_enter_serial())
                 .unwrap();
 
-            pointer.pointer().set_cursor(
-                serial,
-                Some(surface),
-                cursor.hotspot_x / scale,
-                cursor.hotspot_y / scale,
-            );
+            let hotspot =
+                PhysicalPosition::new(cursor.hotspot_x, cursor.hotspot_y).to_logical(scale);
+            pointer.pointer().set_cursor(serial, Some(surface), hotspot.x, hotspot.y);
         });
     }