Bug 1606771 - Fix the middle area of border-image nine-patches. r=gw

Unlike the border areas that only nead their own dimensions, the middle area of a border-image determines its repetition parameter based on the size of the borders. A new flag is provided for the brush_image shader to know whether to use the segment's own rect or look at the borders when computing the pattern's size.

Differential Revision: https://phabricator.services.mozilla.com/D59675

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/834d49acd3c02a7e5ae75d0a4d01a55e69c8fdba

webrender/res/brush.glsl

@@ -114,7 +114,8 @@ void multi_brush_vs(
 #define BRUSH_FLAG_SEGMENT_REPEAT_Y             8
 #define BRUSH_FLAG_SEGMENT_REPEAT_X_ROUND      16
 #define BRUSH_FLAG_SEGMENT_REPEAT_Y_ROUND      32
-#define BRUSH_FLAG_TEXEL_RECT                  64
+#define BRUSH_FLAG_SEGMENT_NINEPATCH_MIDDLE    64
+#define BRUSH_FLAG_TEXEL_RECT                 128
 
 #define INVALID_SEGMENT_INDEX                   0xffff
 

webrender/res/brush_image.glsl

@@ -104,13 +104,39 @@ void image_brush_vs(
             uv1 = res.uv_rect.p0 + segment_data.zw * uv_size;
 
             #ifdef WR_FEATURE_REPETITION
+            // The repetition parameters for the middle area of a nine-patch are based
+            // on the size of the border segments rather than the middle segment itself,
+            // taking top and left by default, falling back to bottom and right when a
+            // size is empty.
+            // TODO(bug 1609893): Move this logic of the CPU as well as other sources of
+            // branchiness in this shader.
+            if ((brush_flags & BRUSH_FLAG_SEGMENT_NINEPATCH_MIDDLE) != 0) {
+                dx = segment_data.x;
+                dy = segment_data.y;
+                stretch_size.x = segment_rect.p0.x - prim_rect.p0.x;
+                stretch_size.y = segment_rect.p0.y - prim_rect.p0.y;
+                float epsilon = 0.001;
+                if (dx < epsilon || stretch_size.x < epsilon) {
+                    dx = 1.0 - segment_data.z;
+                    stretch_size.x = prim_rect.p0.x + prim_rect.size.x
+                        - segment_rect.p0.x - segment_rect.size.x;
+                }
+                if (dy < epsilon || stretch_size.y < epsilon) {
+                    dy = 1.0 - segment_data.w;
+                    stretch_size.y = prim_rect.p0.y + prim_rect.size.y
+                        - segment_rect.p0.y - segment_rect.size.y;
+                }
+            }
+
+            vec2 original_stretch_size = stretch_size;
             if ((brush_flags & BRUSH_FLAG_SEGMENT_REPEAT_X) != 0) {
-              stretch_size.x = local_rect.size.y / dy * dx;
+              stretch_size.x = original_stretch_size.y / dy * dx;
             }
             if ((brush_flags & BRUSH_FLAG_SEGMENT_REPEAT_Y) != 0) {
-              stretch_size.y = local_rect.size.x / dx * dy;
+              stretch_size.y = original_stretch_size.x / dx * dy;
             }
             #endif
+
         } else {
             #ifdef WR_FEATURE_REPETITION
             if ((brush_flags & BRUSH_FLAG_SEGMENT_REPEAT_X) != 0) {

webrender/src/border.rs

@@ -1349,7 +1349,8 @@ impl NinePatchDescriptor {
             rect: LayoutRect,
             uv_rect: TexelRect,
             repeat_horizontal: RepeatMode,
-            repeat_vertical: RepeatMode
+            repeat_vertical: RepeatMode,
+            extra_flags: BrushFlags,
         ) {
             if uv_rect.uv1.x < uv_rect.uv0.x || uv_rect.uv1.y < uv_rect.uv0.y {
                 return;
@@ -1359,7 +1360,8 @@ impl NinePatchDescriptor {
             // instances in this primitive.
             let mut brush_flags =
                 BrushFlags::SEGMENT_RELATIVE |
-                BrushFlags::SEGMENT_TEXEL_RECT;
+                BrushFlags::SEGMENT_TEXEL_RECT |
+                extra_flags;
 
             // Enable repeat modes on the segment.
             if repeat_horizontal == RepeatMode::Repeat {
@@ -1399,31 +1401,35 @@ impl NinePatchDescriptor {
             LayoutRect::from_floats(tl_outer.x, tl_outer.y, tl_inner.x, tl_inner.y),
             TexelRect::new(px0, py0, px1, py1),
             RepeatMode::Stretch,
-            RepeatMode::Stretch
+            RepeatMode::Stretch,
+            BrushFlags::empty(),
         );
         // Top right
         add_segment(
             &mut segments,
             LayoutRect::from_floats(tr_inner.x, tr_outer.y, tr_outer.x, tr_inner.y),
             TexelRect::new(px2, py0, px3, py1),
             RepeatMode::Stretch,
-            RepeatMode::Stretch
+            RepeatMode::Stretch,
+            BrushFlags::empty(),
         );
         // Bottom right
         add_segment(
             &mut segments,
             LayoutRect::from_floats(br_inner.x, br_inner.y, br_outer.x, br_outer.y),
             TexelRect::new(px2, py2, px3, py3),
             RepeatMode::Stretch,
-            RepeatMode::Stretch
+            RepeatMode::Stretch,
+            BrushFlags::empty(),
         );
         // Bottom left
         add_segment(
             &mut segments,
             LayoutRect::from_floats(bl_outer.x, bl_inner.y, bl_inner.x, bl_outer.y),
             TexelRect::new(px0, py2, px1, py3),
             RepeatMode::Stretch,
-            RepeatMode::Stretch
+            RepeatMode::Stretch,
+            BrushFlags::empty(),
         );
 
         // Center
@@ -1433,7 +1439,8 @@ impl NinePatchDescriptor {
                 LayoutRect::from_floats(tl_inner.x, tl_inner.y, tr_inner.x, bl_inner.y),
                 TexelRect::new(px1, py1, px2, py2),
                 self.repeat_horizontal,
-                self.repeat_vertical
+                self.repeat_vertical,
+                BrushFlags::SEGMENT_NINEPATCH_MIDDLE,
             );
         }
 
@@ -1446,6 +1453,7 @@ impl NinePatchDescriptor {
             TexelRect::new(px1, py0, px2, py1),
             self.repeat_horizontal,
             RepeatMode::Stretch,
+            BrushFlags::empty(),
         );
         // Bottom
         add_segment(
@@ -1454,6 +1462,7 @@ impl NinePatchDescriptor {
             TexelRect::new(px1, py2, px2, py3),
             self.repeat_horizontal,
             RepeatMode::Stretch,
+            BrushFlags::empty(),
         );
         // Left
         add_segment(
@@ -1462,6 +1471,7 @@ impl NinePatchDescriptor {
             TexelRect::new(px0, py1, px1, py2),
             RepeatMode::Stretch,
             self.repeat_vertical,
+            BrushFlags::empty(),
         );
         // Right
         add_segment(
@@ -1470,6 +1480,7 @@ impl NinePatchDescriptor {
             TexelRect::new(px2, py1, px3, py2),
             RepeatMode::Stretch,
             self.repeat_vertical,
+            BrushFlags::empty(),
         );
 
         segments

webrender/src/gpu_types.rs

@@ -411,12 +411,14 @@ bitflags! {
         const SEGMENT_REPEAT_X = 4;
         /// Repeat UVs vertically.
         const SEGMENT_REPEAT_Y = 8;
-        /// Horizontally follow border-image-repeat: round
+        /// Horizontally follow border-image-repeat: round.
         const SEGMENT_REPEAT_X_ROUND = 16;
-        /// Vorizontally follow border-image-repeat: round
+        /// Vertically follow border-image-repeat: round.
         const SEGMENT_REPEAT_Y_ROUND = 32;
+        /// Middle (fill) area of a border-image-repeat.
+        const SEGMENT_NINEPATCH_MIDDLE = 64;
         /// The extra segment data is a texel rect.
-        const SEGMENT_TEXEL_RECT = 64;
+        const SEGMENT_TEXEL_RECT = 128;
     }
 }