openxr: support changing overlay opacity

src/backend/openxr/lines.rs

@@ -135,10 +135,11 @@ impl LinePool {
             if let Some(inner) = line.maybe_line.take() {
                 let quad = xr::CompositionLayerQuad::new()
                     .pose(inner.pose)
-                    .sub_image(
-                        line.swapchain
-                            .acquire_present_release(command_buffer, inner.view),
-                    )
+                    .sub_image(line.swapchain.acquire_present_release(
+                        command_buffer,
+                        inner.view,
+                        1.0,
+                    ))
                     .eye_visibility(xr::EyeVisibility::BOTH)
                     .layer_flags(xr::CompositionLayerFlags::CORRECT_CHROMATIC_ABERRATION)
                     .space(&xr.stage)

src/backend/openxr/overlay.rs

@@ -50,7 +50,7 @@ impl OverlayData<OpenXrOverlayData> {
             srd
         });
 
-        let sub_image = data.acquire_present_release(command_buffer, my_view);
+        let sub_image = data.acquire_present_release(command_buffer, my_view, self.state.alpha);
         let posef = helpers::transform_to_posef(&self.state.transform);
 
         let aspect_ratio = extent[1] as f32 / extent[0] as f32;

src/backend/openxr/swapchain.rs

@@ -87,6 +87,7 @@ impl SwapchainRenderData {
         &mut self,
         command_buffer: &mut WlxCommandBuffer,
         view: Arc<ImageView>,
+        alpha: f32,
     ) -> xr::SwapchainSubImage<xr::Vulkan> {
         let idx = self.swapchain.acquire_image().unwrap() as usize;
         self.swapchain.wait_image(xr::Duration::INFINITE).unwrap();
@@ -95,14 +96,18 @@ impl SwapchainRenderData {
         command_buffer.begin_rendering(render_target.clone());
 
         let target_extent = render_target.image().extent();
-        let set = self
+
+        let set0 = self
             .pipeline
             .uniform_sampler(0, view.clone(), Filter::Linear);
+
+        let set1 = self.pipeline.uniform_buffer(1, vec![alpha]);
+
         let pass = self.pipeline.create_pass(
             [target_extent[0] as _, target_extent[1] as _],
             command_buffer.graphics.quad_verts.clone(),
             command_buffer.graphics.quad_indices.clone(),
-            vec![set],
+            vec![set0, set1],
         );
         command_buffer.run_ref(&pass);
         command_buffer.end_rendering();