fix: create fractional scale for sctk subsurfaces

winit/src/platform_specific/wayland/event_loop/state.rs

@@ -518,15 +518,19 @@ impl SctkState {
         let mut id = None;
 
         for subsurface in &self.subsurfaces {
-            if subsurface.instance.parent != surface.id() {
+            if subsurface.instance.wl_surface != *surface {
                 continue;
             }
+            id = Some(subsurface.id);
+            if legacy && subsurface.instance.wp_fractional_scale.is_some() {
+                return;
+            }
+            let mut common = subsurface.common.lock().unwrap();
+            common.fractional_scale = Some(scale_factor);
+            if legacy {
+                subsurface.instance.wl_surface.set_buffer_scale(scale_factor as _);
+            }
 
-            self.sctk_events.push(SctkEvent::SurfaceScaleFactorChanged(
-                scale_factor,
-                surface.clone(),
-                subsurface.id,
-            ));
         }
 
         if let Some(popup) = self
@@ -1575,6 +1579,10 @@ impl SctkState {
             &self.queue_handle,
             cctk::sctk::globals::GlobalData,
         );
+        let wp_fractional_scale =
+            self.fractional_scaling_manager.as_ref().map(|fsm| {
+                fsm.fractional_scaling(&wl_surface, &self.queue_handle)
+            });
 
         let wp_alpha_modifier_surface = subsurface_state
             .wp_alpha_modifier
@@ -1595,6 +1603,7 @@ impl SctkState {
             wl_subsurface: wl_subsurface.clone(),
             wp_viewport: wp_viewport.clone(),
             wp_alpha_modifier_surface: wp_alpha_modifier_surface,
+            wp_fractional_scale,
 
             wl_buffer: None,
             bounds: Some(bounds),

winit/src/platform_specific/wayland/subsurface_widget.rs

@@ -48,6 +48,7 @@ use wayland_protocols::wp::{
         wp_alpha_modifier_surface_v1::WpAlphaModifierSurfaceV1,
         wp_alpha_modifier_v1::WpAlphaModifierV1,
     },
+    fractional_scale::v1::client::wp_fractional_scale_v1::WpFractionalScaleV1,
     linux_dmabuf::zv1::client::{
         zwp_linux_buffer_params_v1::{self, ZwpLinuxBufferParamsV1},
         zwp_linux_dmabuf_v1::{self, ZwpLinuxDmabufV1},
@@ -455,6 +456,7 @@ impl SubsurfaceState {
             wp_alpha_modifier_surface,
             wl_buffer: None,
             bounds: None,
+            wp_fractional_scale: None,
             transform: wl_output::Transform::Normal,
             z: 0,
             parent: parent.id(),
@@ -612,6 +614,7 @@ pub(crate) struct SubsurfaceInstance {
     pub(crate) wl_surface: WlSurface,
     pub(crate) wl_subsurface: WlSubsurface,
     pub(crate) wp_viewport: WpViewport,
+    pub(crate) wp_fractional_scale: Option<WpFractionalScaleV1>,
     pub(crate) wp_alpha_modifier_surface: Option<WpAlphaModifierSurfaceV1>,
     pub(crate) wl_buffer: Option<WlBuffer>,
     pub(crate) bounds: Option<Rectangle<f32>>,