Bug 1543844 - Fix incorrect max scale detection in WR border rendering. r=emilio

The local rect for border segments is not solely determined by
the widths and/or radius. Instead of determining the max scale
based on those parameters, use the calculated border segment
rects to determine an appropriate max scale factor.

Differential Revision: https://phabricator.services.mozilla.com/D27189

--HG--
extra : moz-landing-system : lando

gfx/wr/webrender/src/border.rs

@@ -11,7 +11,7 @@ use display_list_flattener::DisplayListFlattener;
 use gpu_types::{BorderInstance, BorderSegment, BrushFlags};
 use prim_store::{BorderSegmentInfo, BrushSegment, NinePatchDescriptor};
 use prim_store::{EdgeAaSegmentMask, ScrollNodeAndClipChain};
-use prim_store::borders::NormalBorderPrim;
+use prim_store::borders::{NormalBorderPrim, NormalBorderData};
 use util::{lerp, RectHelpers};
 
 // Using 2048 as the maximum radius in device space before which we
@@ -872,21 +872,13 @@ pub fn create_border_segments(
 /// resolution and stretching them, so they will have the right shape, but
 /// blurrier.
 pub fn get_max_scale_for_border(
-    radii: &BorderRadius,
-    widths: &LayoutSideOffsets
+    border_data: &NormalBorderData,
 ) -> LayoutToDeviceScale {
-    let r = radii.top_left.width
-        .max(radii.top_left.height)
-        .max(radii.top_right.width)
-        .max(radii.top_right.height)
-        .max(radii.bottom_left.width)
-        .max(radii.bottom_left.height)
-        .max(radii.bottom_right.width)
-        .max(radii.bottom_right.height)
-        .max(widths.top)
-        .max(widths.bottom)
-        .max(widths.left)
-        .max(widths.right);
+    let mut r = 1.0;
+    for segment in &border_data.border_segments {
+        let size = segment.local_task_size;
+        r = size.width.max(size.height.max(r));
+    }
 
     LayoutToDeviceScale::new(MAX_BORDER_RESOLUTION as f32 / r)
 }

gfx/wr/webrender/src/prim_store/mod.rs

@@ -2583,8 +2583,7 @@ impl PrimitiveStore {
                 // Pick the maximum dimension as scale
                 let world_scale = LayoutToWorldScale::new(scale_width.max(scale_height));
                 let mut scale = world_scale * device_pixel_scale;
-                let max_scale = get_max_scale_for_border(&border_data.border.radius,
-                                                         &border_data.widths);
+                let max_scale = get_max_scale_for_border(border_data);
                 scale.0 = scale.0.min(max_scale.0);
 
                 // For each edge and corner, request the render task by content key

gfx/wr/wrench/reftests/border/max-scale-ref.yaml

@@ -0,0 +1,9 @@
+---
+root:
+  items:
+    - type: border
+      bounds: [ 0, 0, 4000, 1 ]
+      width: [ 1, 0, 0, 0 ]
+      border-type: normal
+      style: solid
+      color: red

gfx/wr/wrench/reftests/border/max-scale.yaml

@@ -0,0 +1,12 @@
+---
+root:
+  items:
+    - type: stacking-context
+      transform: scale(3000, 1)
+      items:
+        - type: border
+          bounds: [ 0, 0, 100, 100 ]
+          width: [ 1, 0, 0, 0 ]
+          border-type: normal
+          style: solid
+          color: red

gfx/wr/wrench/reftests/border/reftest.list

@@ -28,3 +28,4 @@ platform(linux,mac) == border-dashed-dotted-caching.yaml border-dashed-dotted-ca
 != small-inset-outset.yaml small-inset-outset-notref.yaml
 == no-aa.yaml green-square.yaml
 border-double-1px.yaml border-double-1px-ref.yaml
+== max-scale.yaml max-scale-ref.yaml