Auto merge of #1693 - mephisto41:transform3d-clipping, r=kvark

If the transform contains perspective component, the clip rect don't affect by this transform.

When calculating the LCCR. If current transform or parent transform has
perspective component, then we shouldn't transform the LCCR by this
transform because we only consider 2d component for LCCR. Once the
perspective component is presence, the LCCR would be wrong.

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webrender/src/tiling.rs

@@ -26,7 +26,8 @@ use renderer::ImageBufferKind;
 use resource_cache::{GlyphFetchResult, ResourceCache};
 use std::{cmp, usize, f32, i32};
 use texture_allocator::GuillotineAllocator;
-use util::{TransformedRect, TransformedRectKind};
+use util::{MatrixHelpers, TransformedRect, TransformedRectKind};
+use euclid::rect;
 
 // Special sentinel value recognized by the shader. It is considered to be
 // a dummy task that doesn't mask out anything.
@@ -1690,7 +1691,13 @@ impl PackedLayer {
         screen_rect: &DeviceIntRect,
         device_pixel_ratio: f32,
     ) -> Option<(TransformedRectKind, DeviceIntRect)> {
-        self.local_clip_rect = *local_rect;
+        self.local_clip_rect = if self.transform.has_perspective_component() {
+            // Given a very large rect which means any rect would be inside this rect.
+            // That is, nothing would be clipped.
+            rect(f32::MIN / 2.0, f32::MIN / 2.0, f32::MAX, f32::MAX)
+        } else {
+            *local_rect
+        };
         let xf_rect = TransformedRect::new(local_rect, &self.transform, device_pixel_ratio);
         xf_rect
             .bounding_rect

webrender/src/util.rs

@@ -17,6 +17,7 @@ pub trait MatrixHelpers<Src, Dst> {
     fn transform_rect(&self, rect: &TypedRect<f32, Src>) -> TypedRect<f32, Dst>;
     fn is_identity(&self) -> bool;
     fn preserves_2d_axis_alignment(&self) -> bool;
+    fn has_perspective_component(&self) -> bool;
     fn inverse_project(&self, target: &TypedPoint2D<f32, Dst>) -> Option<TypedPoint2D<f32, Src>>;
     fn inverse_rect_footprint(&self, rect: &TypedRect<f32, Dst>) -> TypedRect<f32, Src>;
 }
@@ -66,6 +67,10 @@ impl<Src, Dst> MatrixHelpers<Src, Dst> for TypedTransform3D<f32, Src, Dst> {
         col0 < 2 && col1 < 2 && row0 < 2 && row1 < 2
     }
 
+    fn has_perspective_component(&self) -> bool {
+         self.m14 != 0.0 || self.m24 != 0.0 || self.m34 != 0.0 || self.m44 != 1.0
+    }
+
     fn inverse_project(&self, target: &TypedPoint2D<f32, Dst>) -> Option<TypedPoint2D<f32, Src>> {
         let m: TypedTransform2D<f32, Src, Dst>;
         m = TypedTransform2D::column_major(

wrench/reftests/split/perspective-clipping-ref.yaml

@@ -0,0 +1,9 @@
+---
+root:
+  items:
+    - type: stacking-context
+      bounds: 0 0 1024 768
+      items:
+        - type: rect
+          bounds: 0 0 1024 768
+          color: green

wrench/reftests/split/perspective-clipping.yaml

@@ -0,0 +1,22 @@
+---
+root:
+  items:
+    - type: stacking-context
+      bounds: 0 0 1024 768
+      items:
+        - type: rect
+          bounds: 0 0 1024 768
+          color: red
+        - type: stacking-context
+          bounds: 0 0 1024 768
+          transform-style: preserve-3d
+          perspective: 300
+          items:
+            - type: stacking-context
+              bounds: 0 0 1024 768
+              # translate-Z(-300) scale(2)
+              transform: 2 0 0 0 0 2 0 0 0 0 2 0 0 0 -300 1
+              items:
+                - type: rect
+                  bounds: 0 0 1024 768
+                  color: green

wrench/reftests/split/reftest.list

@@ -2,4 +2,5 @@
 == order.yaml order-ref.yaml
 == nested.yaml nested-ref.yaml
 == nested-preserve3d-crash.yaml nested-preserve3d-crash.yaml
+== perspective-clipping.yaml perspective-clipping-ref.yaml
 #== cross.yaml cross-ref.yaml #TODO: investigate sub-pixel differences