Auto merge of #3868 - moz-gfx:github-sync, r=auto

Sync changes from mozilla-central gfx/wr

 Fixes #3864,

webrender/res/brush.glsl

@@ -164,8 +164,12 @@ void main(void) {
 
     // Write the normal vertex information out.
     if (transform.is_axis_aligned) {
+
+        // Select the corner of the local rect that we are processing.
+        vec2 local_pos = segment_rect.p0 + segment_rect.size * aPosition.xy;
+
         vi = write_vertex(
-            segment_rect,
+            local_pos,
             ph.local_clip_rect,
             ph.z,
             transform,

webrender/res/prim_shared.glsl

@@ -109,15 +109,11 @@ struct VertexInfo {
     vec4 world_pos;
 };
 
-VertexInfo write_vertex(RectWithSize instance_rect,
+VertexInfo write_vertex(vec2 local_pos,
                         RectWithSize local_clip_rect,
                         float z,
                         Transform transform,
                         PictureTask task) {
-
-    // Select the corner of the local rect that we are processing.
-    vec2 local_pos = instance_rect.p0 + instance_rect.size * aPosition.xy;
-
     // Clamp to the two local clip rects.
     vec2 clamped_local_pos = clamp_rect(local_pos, local_clip_rect);
 

webrender/res/ps_text_run.glsl

@@ -90,6 +90,28 @@ TextRun fetch_text_run(int address) {
     return TextRun(data[0], data[1]);
 }
 
+vec2 get_snap_bias(int subpx_dir) {
+    // In subpixel mode, the subpixel offset has already been
+    // accounted for while rasterizing the glyph. However, we
+    // must still round with a subpixel bias rather than rounding
+    // to the nearest whole pixel, depending on subpixel direciton.
+    switch (subpx_dir) {
+        case SUBPX_DIR_NONE:
+        default:
+            return vec2(0.5);
+        case SUBPX_DIR_HORIZONTAL:
+            // Glyphs positioned [-0.125, 0.125] get a
+            // subpx position of zero. So include that
+            // offset in the glyph position to ensure
+            // we round to the correct whole position.
+            return vec2(0.125, 0.5);
+        case SUBPX_DIR_VERTICAL:
+            return vec2(0.5, 0.125);
+        case SUBPX_DIR_MIXED:
+            return vec2(0.125);
+    }
+}
+
 void main(void) {
     Instance instance = decode_instance_attributes();
 
@@ -118,30 +140,7 @@ void main(void) {
 
     GlyphResource res = fetch_glyph_resource(instance.resource_address);
 
-    vec2 snap_bias;
-    // In subpixel mode, the subpixel offset has already been
-    // accounted for while rasterizing the glyph. However, we
-    // must still round with a subpixel bias rather than rounding
-    // to the nearest whole pixel, depending on subpixel direciton.
-    switch (subpx_dir) {
-        case SUBPX_DIR_NONE:
-        default:
-            snap_bias = vec2(0.5);
-            break;
-        case SUBPX_DIR_HORIZONTAL:
-            // Glyphs positioned [-0.125, 0.125] get a
-            // subpx position of zero. So include that
-            // offset in the glyph position to ensure
-            // we round to the correct whole position.
-            snap_bias = vec2(0.125, 0.5);
-            break;
-        case SUBPX_DIR_VERTICAL:
-            snap_bias = vec2(0.5, 0.125);
-            break;
-        case SUBPX_DIR_MIXED:
-            snap_bias = vec2(0.125);
-            break;
-    }
+    vec2 snap_bias = get_snap_bias(subpx_dir);
 
     // Glyph space refers to the pixel space used by glyph rasterization during frame
     // building. If a non-identity transform was used, WR_FEATURE_GLYPH_TRANSFORM will
@@ -220,26 +219,22 @@ void main(void) {
     vec2 local_pos = glyph_rect.p0 + glyph_rect.size * aPosition.xy;
 #endif
 
-    // Clamp to the local clip rect.
-    local_pos = clamp_rect(local_pos, ph.local_clip_rect);
-
-    // Map the clamped local space corner into device space.
-    vec4 world_pos = transform.m * vec4(local_pos, 0.0, 1.0);
-    vec2 device_pos = world_pos.xy * task.device_pixel_scale;
-
-    // Apply offsets for the render task to get correct screen location.
-    vec2 final_offset = -task.content_origin + task.common_data.task_rect.p0;
-
-    gl_Position = uTransform * vec4(device_pos + final_offset * world_pos.w, ph.z * world_pos.w, world_pos.w);
+    VertexInfo vi = write_vertex(
+        local_pos,
+        ph.local_clip_rect,
+        ph.z,
+        transform,
+        task
+    );
 
 #ifdef WR_FEATURE_GLYPH_TRANSFORM
-    vec2 f = (glyph_transform * local_pos - glyph_rect.p0) / glyph_rect.size;
+    vec2 f = (glyph_transform * vi.local_pos - glyph_rect.p0) / glyph_rect.size;
     V_UV_CLIP = vec4(f, 1.0 - f);
 #else
-    vec2 f = (local_pos - glyph_rect.p0) / glyph_rect.size;
+    vec2 f = (vi.local_pos - glyph_rect.p0) / glyph_rect.size;
 #endif
 
-    write_clip(world_pos, clip_area);
+    write_clip(vi.world_pos, clip_area);
 
     switch (color_mode) {
         case COLOR_MODE_ALPHA: