Ensure that non-local clips are defaulted to be in the clip mask.

If we can't calculate a local space rect for the clip, due to
perspective weirdness, just assume that it should be in the
clip mask, for now.

webrender/src/clip.rs

@@ -556,52 +556,63 @@ impl ClipStore {
             let node = &mut self.clip_nodes[node_info.node_index.0 as usize];
 
             // Convert the prim rect into the clip nodes local space
-            if let Some(prim_rect) = node_info
+            let prim_rect = node_info
                 .conversion
-                .transform_from_prim_space(&current_local_clip_rect) {
+                .transform_from_prim_space(&current_local_clip_rect);
 
-                // See how this clip affects the prim region.
-                let clip_result = node.item.get_clip_result(&prim_rect);
+            // See how this clip affects the prim region.
+            let clip_result = match prim_rect {
+                Some(prim_rect) => {
+                    node.item.get_clip_result(&prim_rect)
+                }
+                None => {
+                    // If we can't get a local rect due to perspective
+                    // weirdness, just assume that we need a clip mask
+                    // for this case.
+                    // TODO(gw): We can probably improve on this once
+                    //           we support local space picture raster.
+                    ClipResult::Partial
+                }
+            };
 
-                match clip_result {
-                    ClipResult::Accept => {
-                        // Doesn't affect the primitive at all, so skip adding to list
-                    }
-                    ClipResult::Reject => {
-                        // Completely clips the supplied prim rect
-                        return None;
-                    }
-                    ClipResult::Partial => {
-                        // Needs a mask -> add to clip node indices
-
-                        // TODO(gw): Ensure this only runs once on each node per frame?
-                        node.update(
-                            gpu_cache,
-                            resource_cache,
-                            device_pixel_scale,
-                        );
-
-                        // Calculate some flags that are required for the segment
-                        // building logic.
-                        let flags = match node_info.conversion {
-                            ClipSpaceConversion::Local => {
-                                ClipNodeFlags::SAME_SPATIAL_NODE | ClipNodeFlags::SAME_COORD_SYSTEM
-                            }
-                            ClipSpaceConversion::Offset(..) => {
-                                ClipNodeFlags::SAME_COORD_SYSTEM
-                            }
-                            ClipSpaceConversion::Transform(..) => {
-                                has_clips_from_other_coordinate_systems = true;
-                                ClipNodeFlags::empty()
-                            }
-                        };
+            match clip_result {
+                ClipResult::Accept => {
+                    // Doesn't affect the primitive at all, so skip adding to list
+                }
+                ClipResult::Reject => {
+                    // Completely clips the supplied prim rect
+                    return None;
+                }
+                ClipResult::Partial => {
+                    // Needs a mask -> add to clip node indices
+
+                    // TODO(gw): Ensure this only runs once on each node per frame?
+                    node.update(
+                        gpu_cache,
+                        resource_cache,
+                        device_pixel_scale,
+                    );
+
+                    // Calculate some flags that are required for the segment
+                    // building logic.
+                    let flags = match node_info.conversion {
+                        ClipSpaceConversion::Local => {
+                            ClipNodeFlags::SAME_SPATIAL_NODE | ClipNodeFlags::SAME_COORD_SYSTEM
+                        }
+                        ClipSpaceConversion::Offset(..) => {
+                            ClipNodeFlags::SAME_COORD_SYSTEM
+                        }
+                        ClipSpaceConversion::Transform(..) => {
+                            has_clips_from_other_coordinate_systems = true;
+                            ClipNodeFlags::empty()
+                        }
+                    };
 
-                        // Store this in the index buffer for this clip chain instance.
-                        self.clip_node_indices
-                            .push(ClipNodeInstance::new(node_info.node_index, flags));
+                    // Store this in the index buffer for this clip chain instance.
+                    self.clip_node_indices
+                        .push(ClipNodeInstance::new(node_info.node_index, flags));
 
-                        has_non_root_coord_system |= node_info.has_non_root_coord_system;
-                    }
+                    has_non_root_coord_system |= node_info.has_non_root_coord_system;
                 }
             }
         }

wrench/reftests/transforms/perspective-mask.yaml

@@ -0,0 +1,22 @@
+---
+root:
+  items:
+    -
+      type: "scroll-frame"
+      id: 2
+      "content-size": [500, 100]
+      bounds: [0, 0, 500, 100]
+      items:
+        -
+          type: "stacking-context"
+          perspective: 125
+          items:
+            -
+              type: "stacking-context"
+              bounds: [0, 0, 250, 100]
+              transform: rotate-y(-54)
+              items:
+                -
+                  bounds: [0, 0, 128, 128]
+                  type: rect
+                  color: red

wrench/reftests/transforms/reftest.list

@@ -18,3 +18,4 @@ platform(linux) fuzzy(11,4592) == screen-space-blur.yaml screen-space-blur.png
 platform(linux,mac) == nested-rotate-x.yaml nested-rotate-x.png
 platform(linux,mac) == nested-preserve-3d.yaml nested-preserve-3d.png
 platform(linux,mac) == near-plane-clip.yaml near-plane-clip.png
+platform(linux,mac) == perspective-mask.yaml perspective-mask.png