Bug 1942959 - Fix clip rect that is applied to external swap chains with layer compositor enabled r=gfx-reviewers,lsalzman

Differential Revision: https://phabricator.services.mozilla.com/D235096

Author: Glenn Watson

webrender/src/composite.rs

@@ -1363,8 +1363,10 @@ pub trait Compositor {
 // implemention should prepare
 #[derive(Debug)]
 pub struct CompositorInputLayer {
-    // Device space location and size of the layer
-    pub rect: DeviceIntRect,
+    // Device space location of the layer (pre-clip)
+    pub offset: DeviceIntPoint,
+    // Device space clip-rect of the layer
+    pub clip_rect: DeviceIntRect,
     // Whether a content or external surface
     pub usage: CompositorSurfaceUsage,
     // If true, layer is opaque, blend can be disabled

webrender/src/renderer/mod.rs

@@ -3588,24 +3588,27 @@ impl Renderer {
             };
 
             if let Some(new_layer_kind) = new_layer_kind {
-                let (rect, is_opaque) = match usage {
+                let (offset, clip_rect, is_opaque) = match usage {
                     CompositorSurfaceUsage::Content => {
-                        (device_size.into(), input_layers.is_empty())
+                        (DeviceIntPoint::zero(), device_size.into(), input_layers.is_empty())
                     }
                     CompositorSurfaceUsage::External { .. } => {
                         let rect = composite_state.get_device_rect(
                             &tile.local_rect,
                             tile.transform_index
                         );
 
-                        (rect.to_i32(), is_opaque)
+                        let clip_rect = tile.device_clip_rect.to_i32();
+
+                        (rect.min.to_i32(), clip_rect, is_opaque)
                     }
                 };
 
                 input_layers.push(CompositorInputLayer {
                     usage: new_layer_kind,
                     is_opaque,
-                    rect,
+                    offset,
+                    clip_rect,
                 });
 
                 swapchain_layers.push(SwapChainLayer {
@@ -3635,7 +3638,8 @@ impl Renderer {
             input_layers.push(CompositorInputLayer {
                 usage: CompositorSurfaceUsage::Content,
                 is_opaque: true,
-                rect: device_size.into(),
+                offset: DeviceIntPoint::zero(),
+                clip_rect: device_size.into(),
             });
 
             swapchain_layers.push(SwapChainLayer {
@@ -3675,7 +3679,7 @@ impl Renderer {
                     compositor.bind_layer(layer_index);
 
                     DrawTarget::NativeSurface {
-                        offset: -layer.rect.min,
+                        offset: -layer.offset,
                         external_fbo_id: 0,
                         dimensions: fb_draw_target.dimensions(),
                     }
@@ -3718,7 +3722,7 @@ impl Renderer {
                 compositor.add_surface(
                     layer_index,
                     transform,
-                    layer.rect,
+                    layer.clip_rect,
                     ImageRendering::Auto,
                 );
             }