Raster PictureLayerTiling with fractional translation

cc/layers/picture_layer_impl.cc

Index: cc/layers/picture_layer_impl.cc
diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index 44b594f8a42db1ed7b372dd88d7454cc65eaecad..5cd14b3f6532ac463414485372914ed03ab4bfb2 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -109,6 +109,7 @@ PictureLayerImpl::PictureLayerImpl(LayerTreeImpl* tree_impl,
       only_used_low_res_last_append_quads_(false),
       mask_type_(mask_type),
       nearest_neighbor_(false),
+      use_transformed_rasterization_(false),
       is_directly_composited_image_(false) {
   layer_tree_impl()->RegisterPictureLayerImpl(this);
 }
@@ -145,6 +146,7 @@ void PictureLayerImpl::PushPropertiesTo(LayerImpl* base_layer) {
   layer_impl->twin_layer_ = this;
 
   layer_impl->SetNearestNeighbor(nearest_neighbor_);
+  layer_impl->SetUseTransformedRasterization(use_transformed_rasterization_);
 
   // Solid color layers have no tilings.
   DCHECK(!raster_source_->IsSolidColor() || tilings_->num_tilings() == 0);
@@ -275,7 +277,7 @@ void PictureLayerImpl::AppendQuads(RenderPass* render_pass,
         } else if (iter.resolution() == LOW_RESOLUTION) {
           color = DebugColors::LowResTileBorderColor();
           width = DebugColors::LowResTileBorderWidth(device_scale_factor);
-        } else if (iter->contents_scale() > max_contents_scale) {
+        } else if (iter->contents_scale_key() > max_contents_scale) {
           color = DebugColors::ExtraHighResTileBorderColor();
           width = DebugColors::ExtraHighResTileBorderWidth(device_scale_factor);
         } else {
@@ -343,8 +345,8 @@ void PictureLayerImpl::AppendQuads(RenderPass* render_pass,
           // complete. But if a tile is ideal scale, we don't want to consider
           // it incomplete and trying to replace it with a tile at a worse
           // scale.
-          if (iter->contents_scale() != raster_contents_scale_ &&
-              iter->contents_scale() != ideal_contents_scale_ &&
+          if (iter->contents_scale_key() != raster_contents_scale_ &&
+              iter->contents_scale_key() != ideal_contents_scale_ &&
               geometry_rect.Intersects(scaled_viewport_for_tile_priority)) {
             append_quads_data->num_incomplete_tiles++;
           }
@@ -644,19 +646,22 @@ bool PictureLayerImpl::RasterSourceUsesLCDText() const {
 }
 
 void PictureLayerImpl::NotifyTileStateChanged(const Tile* tile) {
-  if (layer_tree_impl()->IsActiveTree()) {
-    gfx::Rect layer_damage_rect = gfx::ScaleToEnclosingRect(
-        tile->content_rect(), 1.f / tile->contents_scale());
-    AddDamageRect(layer_damage_rect);
-  }
+  if (layer_tree_impl()->IsActiveTree())
+    AddDamageRect(tile->enclosing_layer_rect());
   if (tile->draw_info().NeedsRaster()) {
     PictureLayerTiling* tiling =
-        tilings_->FindTilingWithScaleKey(tile->contents_scale());
+        tilings_->FindTilingWithScaleKey(tile->contents_scale_key());
     if (tiling)
       tiling->set_all_tiles_done(false);
   }
 }
 
+SimpleEnclosedRegion PictureLayerImpl::VisibleOpaqueRegion() const {
+  if (use_transformed_rasterization_)
+    return SimpleEnclosedRegion();
+  return LayerImpl::VisibleOpaqueRegion();
+}
+
 void PictureLayerImpl::DidBeginTracing() {
   raster_source_->DidBeginTracing();
 }
@@ -724,7 +729,13 @@ const PictureLayerTiling* PictureLayerImpl::GetPendingOrActiveTwinTiling(
   PictureLayerImpl* twin_layer = GetPendingOrActiveTwinLayer();
   if (!twin_layer)
     return nullptr;
-  return twin_layer->tilings_->FindTilingWithScaleKey(tiling->contents_scale());
+  const PictureLayerTiling* twin_tiling =
+      twin_layer->tilings_->FindTilingWithScaleKey(
+          tiling->contents_scale_key());
+  if (twin_tiling &&
+      twin_tiling->raster_transform() == tiling->raster_transform())
+    return twin_tiling;
+  return nullptr;
 }
 
 bool PictureLayerImpl::RequiresHighResToDraw() const {
@@ -872,12 +883,21 @@ void PictureLayerImpl::SetNearestNeighbor(bool nearest_neighbor) {
   NoteLayerPropertyChanged();
 }
 
-PictureLayerTiling* PictureLayerImpl::AddTiling(float contents_scale) {
+void PictureLayerImpl::SetUseTransformedRasterization(bool use) {
+  if (use_transformed_rasterization_ == use)
+    return;
+
+  use_transformed_rasterization_ = use;
+  NoteLayerPropertyChanged();
+}
+
+PictureLayerTiling* PictureLayerImpl::AddTiling(
+    const ScaleTranslate2d& contents_transform) {
   DCHECK(CanHaveTilings());
-  DCHECK_GE(contents_scale, MinimumContentsScale());
-  DCHECK_LE(contents_scale, MaximumContentsScale());
+  DCHECK_GE(contents_transform.scale(), MinimumContentsScale());
+  DCHECK_LE(contents_transform.scale(), MaximumContentsScale());
   DCHECK(raster_source_->HasRecordings());
-  return tilings_->AddTiling(contents_scale, raster_source_);
+  return tilings_->AddTiling(contents_transform, raster_source_);
 }
 
 void PictureLayerImpl::RemoveAllTilings() {
@@ -893,9 +913,17 @@ void PictureLayerImpl::AddTilingsForRasterScale() {
 
   PictureLayerTiling* high_res =
       tilings_->FindTilingWithScaleKey(raster_contents_scale_);
+  gfx::Vector2dF raster_translation =
+      CalculateRasterTranslation(raster_contents_scale_);
+  if (high_res &&
+      high_res->raster_transform().translation() != raster_translation) {
+    tilings_->Remove(high_res);
+    high_res = nullptr;
+  }
   if (!high_res) {
     // We always need a high res tiling, so create one if it doesn't exist.
-    high_res = AddTiling(raster_contents_scale_);
+    high_res =
+        AddTiling(ScaleTranslate2d(raster_contents_scale_, raster_translation));
   } else if (high_res->may_contain_low_resolution_tiles()) {
     // If the tiling we find here was LOW_RESOLUTION previously, it may not be
     // fully rastered, so destroy the old tiles.
@@ -992,7 +1020,8 @@ void PictureLayerImpl::AddLowResolutionTilingIfNeeded() {
   bool is_animating = draw_properties().screen_space_transform_is_animating;
   if (!is_pinching && !is_animating) {
     if (!low_res)
-      low_res = AddTiling(low_res_raster_contents_scale_);
+      low_res = AddTiling(
+          ScaleTranslate2d(low_res_raster_contents_scale_, gfx::Vector2dF()));
     low_res->set_resolution(LOW_RESOLUTION);
   }
 }
@@ -1158,6 +1187,34 @@ void PictureLayerImpl::CleanUpTilingsOnActiveLayer(
   SanityCheckTilingState();
 }
 
+gfx::Vector2dF PictureLayerImpl::CalculateRasterTranslation(
+    float raster_scale) {
+  if (!use_transformed_rasterization_)
+    return gfx::Vector2dF();
+
+  DCHECK(!draw_properties().screen_space_transform_is_animating);
+  gfx::Transform draw_transform = DrawTransform();
+  DCHECK(draw_transform.IsScaleOrTranslation());
+
+  // It is only useful to align the content space to the target space if their
+  // relative pixel ratio is some small rational number. Currently we only
+  // align if the relative pixel ratio is 1:1.
+  // Good match if the maximum alignment error on a layer of size 10000px
+  // does not exceed 0.001px.
+  static constexpr float kErrorThreshold = 0.0000001f;
+  if (std::abs(draw_transform.matrix().getFloat(0, 0) - raster_scale) >
+          kErrorThreshold ||
+      std::abs(draw_transform.matrix().getFloat(1, 1) - raster_scale) >
+          kErrorThreshold)
+    return gfx::Vector2dF();
+
+  // Extract the fractional part of layer origin in the target space.
+  float origin_x = draw_transform.matrix().getFloat(0, 3);
+  float origin_y = draw_transform.matrix().getFloat(1, 3);
+  return gfx::Vector2dF(origin_x - floorf(origin_x),
+                        origin_y - floorf(origin_y));
+}
+
 float PictureLayerImpl::MinimumContentsScale() const {
   float setting_min = layer_tree_impl()->settings().minimum_contents_scale;