Sync changes from mozilla-central

webrender/res/ps_text_run.glsl

@@ -63,6 +63,7 @@ TextRun fetch_text_run(int address) {
 
 VertexInfo write_text_vertex(RectWithSize local_clip_rect,
                              float z,
+                             bool should_snap,
                              Transform transform,
                              PictureTask task,
                              vec2 text_offset,
@@ -73,13 +74,8 @@ VertexInfo write_text_vertex(RectWithSize local_clip_rect,
     vec2 snap_offset = vec2(0.0);
     mat2 local_transform;
 
-#ifdef WR_FEATURE_GLYPH_TRANSFORM
-    bool remove_subpx_offset = true;
-#else
-    bool remove_subpx_offset = transform.is_axis_aligned;
-#endif
     // Compute the snapping offset only if the scroll node transform is axis-aligned.
-    if (remove_subpx_offset) {
+    if (should_snap) {
         // Transform from local space to device space.
         float device_scale = task.common_data.device_pixel_scale / transform.m[3].w;
         mat2 device_transform = mat2(transform.m) * device_scale;
@@ -178,13 +174,18 @@ void main(void) {
     RectWithSize glyph_rect = RectWithSize(res.offset + glyph_transform * (text.offset + glyph.offset),
                                            res.uv_rect.zw - res.uv_rect.xy);
 
+    // Since the glyph is pre-transformed, snapping is both forced and does not depend on the transform.
+    bool should_snap = true;
 #else
     // Scale from glyph space to local space.
     float scale = res.scale / task.common_data.device_pixel_scale;
 
     // Compute the glyph rect in local space.
     RectWithSize glyph_rect = RectWithSize(scale * res.offset + text.offset + glyph.offset,
                                            scale * (res.uv_rect.zw - res.uv_rect.xy));
+
+    // Check if the primitive is actually safe to snap.
+    bool should_snap = ph.user_data.x != 0;
 #endif
 
     vec2 snap_bias;
@@ -214,6 +215,7 @@ void main(void) {
 
     VertexInfo vi = write_text_vertex(ph.local_clip_rect,
                                       ph.z,
+                                      should_snap,
                                       transform,
                                       task,
                                       text.offset,

webrender/src/batch.rs

@@ -829,7 +829,7 @@ impl AlphaBatchBuilder {
                             }
                         };
 
-                        let prim_header_index = prim_headers.push(&prim_header, z_id, [0; 3]);
+                        let prim_header_index = prim_headers.push(&prim_header, z_id, [run.should_snap as i32, 0, 0]);
                         let key = BatchKey::new(kind, blend_mode, textures);
                         let base_instance = GlyphInstance::new(
                             prim_header_index,

webrender/src/prim_store/text_run.rs

@@ -65,6 +65,7 @@ impl AsInstanceKind<TextRunDataHandle> for TextRunKey {
             used_font: self.font.clone(),
             glyph_keys_range: storage::Range::empty(),
             shadow: self.shadow,
+            should_snap: true,
         });
 
         PrimitiveInstanceKind::TextRun{ data_handle, run_index }
@@ -227,6 +228,7 @@ pub struct TextRunPrimitive {
     pub used_font: FontInstance,
     pub glyph_keys_range: storage::Range<GlyphKey>,
     pub shadow: bool,
+    pub should_snap: bool,
 }
 
 impl TextRunPrimitive {
@@ -262,6 +264,11 @@ impl TextRunPrimitive {
             FontTransform::identity()
         };
 
+        // We can snap only if the transform is axis-aligned and in screen-space.
+        self.should_snap =
+            transform.preserves_2d_axis_alignment() &&
+            raster_space == RasterSpace::Screen;
+
         // If the transform or device size is different, then the caller of
         // this method needs to know to rebuild the glyphs.
         let cache_dirty =

wrench/reftests/text/raster-space-snap-ref.yaml

@@ -0,0 +1,10 @@
+root:
+  items:
+    - type: stacking-context
+      bounds: [0, 0, 480, 80]
+      raster-space: screen
+      items:
+      - text: "a Bcd Efgh Ijklm Nopqrs Tuvwxyz"
+        origin: 20.5 50
+        size: 20
+        font: "FreeSans.ttf"

wrench/reftests/text/raster-space-snap.yaml

@@ -0,0 +1,10 @@
+root:
+  items:
+    - type: stacking-context
+      bounds: [0, 0, 480, 80]
+      raster-space: local(1.0)
+      items:
+      - text: "a Bcd Efgh Ijklm Nopqrs Tuvwxyz"
+        origin: 20.5 50
+        size: 20
+        font: "FreeSans.ttf"

wrench/reftests/text/reftest.list

@@ -68,3 +68,4 @@ fuzzy(1,113) platform(linux) == raster-space.yaml raster-space.png
 == shadow-image.yaml shadow-solid-ref.yaml
 options(disable-aa) == snap-clip.yaml snap-clip-ref.yaml
 platform(linux) == perspective-clip.yaml perspective-clip.png
+options(disable-subpixel) != raster-space-snap.yaml raster-space-snap-ref.yaml