Add ClipNode when Render Surface Inherits Clip

cc/trees/draw_property_utils.cc

Index: cc/trees/draw_property_utils.cc
diff --git a/cc/trees/draw_property_utils.cc b/cc/trees/draw_property_utils.cc
index 39456bc83bad09fa3d57a8c91b645147a4f29e5d..fe464365fb6d2922de0cdf514273bf721fd265c9 100644
--- a/cc/trees/draw_property_utils.cc
+++ b/cc/trees/draw_property_utils.cc
@@ -57,7 +57,6 @@ void CalculateVisibleRects(const std::vector<LayerType*>& visible_layer_list,
         success = transform_tree.ComputeTransformWithDestinationSublayerScale(
             clip_transform_node->id, target_node->id, &clip_to_target);
       }
-
       if (target_node->id > clip_node->data.transform_id) {
         if (!success) {
           DCHECK(target_node->data.to_screen_is_animated);
@@ -390,6 +389,7 @@ void ComputeClips(ClipTree* clip_tree, const TransformTree& transform_tree) {
     // clip adjusted due to intersecting with an ancestor clip.
     const bool is_clipped = clip_node->parent_id > 0;
     if (!is_clipped) {
+      DCHECK(!clip_node->data.inherit_parent_target_space_clip);
       clip_node->data.combined_clip = clip_node->data.clip;
       continue;
     }
@@ -411,6 +411,8 @@ void ComputeClips(ClipTree* clip_tree, const TransformTree& transform_tree) {
     gfx::Transform parent_to_target;
     gfx::Transform clip_to_target;
     gfx::Transform target_to_clip;
+    gfx::Transform parent_to_transform_target;
+    gfx::Transform transform_target_to_target;
 
     const bool target_is_root_surface = clip_node->data.target_id == 1;
     // When the target is the root surface, we need to include the root
@@ -419,8 +421,21 @@ void ComputeClips(ClipTree* clip_tree, const TransformTree& transform_tree) {
         target_is_root_surface ? 0 : clip_node->data.target_id;
 
     bool success = true;
-    if (parent_transform_node->data.content_target_id ==
-        clip_node->data.target_id) {
+    // When render surface applies clip, we need the clip from the target's
+    // target space. But, as the combined clip is in parent clip's target
+    // space, we need to first transform it from parent's target space to
+    // target's target space.
+    if (clip_node->data.inherit_parent_target_space_clip) {
+      success &= transform_tree.ComputeTransformWithDestinationSublayerScale(
+          parent_transform_node->id, transform_node->data.target_id,
+          &parent_to_transform_target);
+      success &= transform_tree.ComputeTransformWithSourceSublayerScale(

[ajuma, 2015/08/06 14:25:45]

ComputeTransformWithSourceSublayerScale can divide by zero if the source has
sublayer scale zero. I think we've avoided problems with this so far just
because the other caller happens to get skipped when we have zero sublayer
scale. Please add a check for division by zero there (and make it return false
if it's about to divide by zero).

[jaydasika, 2015/08/06 16:39:34]

Done.

+          transform_node->data.target_id, target_id,
+          &transform_target_to_target);
+      transform_target_to_target.Scale(transform_node->data.sublayer_scale.x(),
+                                       transform_node->data.sublayer_scale.y());
+    } else if (parent_transform_node->data.content_target_id ==
+               clip_node->data.target_id) {
       parent_to_target = parent_transform_node->data.to_target;
     } else {
       success &= transform_tree.ComputeTransformWithDestinationSublayerScale(
@@ -444,25 +459,51 @@ void ComputeClips(ClipTree* clip_tree, const TransformTree& transform_tree) {
     // If we can't compute a transform, it's because we had to use the inverse
     // of a singular transform. We won't draw in this case, so there's no need
     // to compute clips.
-    if (!success)
+    if (!success) {
       continue;
+    }
 
     // In order to intersect with as small a rect as possible, we do a
     // preliminary clip in target space so that when we project back, there's
     // less likelihood of intersecting the view plane.
-    gfx::RectF inherited_clip_in_target_space = MathUtil::MapClippedRect(
-        parent_to_target, parent_clip_node->data.combined_clip);
+    gfx::RectF inherited_clip_in_target_space;
+    if (clip_node->data.inherit_parent_target_space_clip) {
+      gfx::RectF combined_clip_in_transform_target_space;
+      if (parent_transform_node->id > transform_node->data.target_id)
+        combined_clip_in_transform_target_space = MathUtil::MapClippedRect(
+            parent_to_transform_target, parent_clip_node->data.combined_clip);
+      else
+        combined_clip_in_transform_target_space = MathUtil::ProjectClippedRect(
+            parent_to_transform_target, parent_clip_node->data.combined_clip);
+      inherited_clip_in_target_space = MathUtil::ProjectClippedRect(
+          transform_target_to_target, combined_clip_in_transform_target_space);
+    } else if (parent_transform_node->id > target_id) {
+      inherited_clip_in_target_space = MathUtil::MapClippedRect(
+          parent_to_target, parent_clip_node->data.combined_clip);
+    } else {
+      inherited_clip_in_target_space = MathUtil::ProjectClippedRect(
+          parent_to_target, parent_clip_node->data.combined_clip);
+    }
 
-    gfx::RectF clip_in_target_space =
-        MathUtil::MapClippedRect(clip_to_target, clip_node->data.clip);
+    // When render surface applies clip, the layer that created the clip node

[ajuma, 2015/08/06 14:25:45]

s/applies clip/inherits its parent's target space clip/

[jaydasika, 2015/08/06 16:39:34]

Done.

+    // doesn't apply any clip. So, we should clip using the clip value

[ajuma, 2015/08/06 14:25:45]

Do you mean "we shouldn't clip" instead? (Since in that case, we're ignoring
data.clip.)

[jaydasika, 2015/08/06 16:39:34]

Done.

+    // stored in the clip node.
+    gfx::RectF intersected_in_target_space;
+    if (!clip_node->data.inherit_parent_target_space_clip) {
+      gfx::RectF clip_in_target_space =
+          MathUtil::MapClippedRect(clip_to_target, clip_node->data.clip);
 
-    gfx::RectF intersected_in_target_space = gfx::IntersectRects(
-        inherited_clip_in_target_space, clip_in_target_space);
+      intersected_in_target_space = gfx::IntersectRects(
+          inherited_clip_in_target_space, clip_in_target_space);
+    } else {
+      intersected_in_target_space = inherited_clip_in_target_space;
+    }
 
     clip_node->data.combined_clip = MathUtil::ProjectClippedRect(
         target_to_clip, intersected_in_target_space);
 
-    clip_node->data.combined_clip.Intersect(clip_node->data.clip);
+    if (!clip_node->data.inherit_parent_target_space_clip)
+      clip_node->data.combined_clip.Intersect(clip_node->data.clip);
   }
   clip_tree->set_needs_update(false);
 }