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 175c33415100440aa966860f8d6a576a48d6f30e..26feaf1c0c738c0946962d8f6dbbf87b042eb558 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);
@@ -388,6 +387,7 @@ 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;
     }
@@ -409,6 +409,8 @@ 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
@@ -417,8 +419,19 @@ 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.ComputeTransformWithDestinationSublayerScale(
+          transform_node->data.target_id, target_id,
+          &transform_target_to_target);
+    } 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(
@@ -442,25 +455,57 @@ 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) {
+      if (clip_node->data.inherit_parent_target_space_clip) {
+        clip_node->data.transform_id = parent_clip_node->data.transform_id;

[ajuma, 2015/08/05 13:51:09]

I don't think we should be changing the transform id here -- that should only
change during tree building. Otherwise, suppose the value of the transform
that's currently uninvertible changes on the next frame, such that it becomes
invertible. If we've changed the transform_id here, we're going to do the wrong
thing, I think.

[jaydasika, 2015/08/05 15:07:20]

Ah, I see the problem. But I am still not sure what the alternative is?

[ajuma, 2015/08/05 15:21:58]

If we reach this point, we have an uninvertible transform, so we just need to
have some reasonable fallback. For example, there are places where CDP pretends
that an uninvertible transform's inverse is the identity. I think the equivalent
here might be to set the combined clip as you do on the next line, but leave the
transform id as-is.

[jaydasika, 2015/08/05 21:50:11]

Done.

+        clip_node->data.combined_clip = parent_clip_node->data.combined_clip;
+      } else {
+        clip_node->data.combined_clip = clip_node->data.clip;
+      }
       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
+    // doesn't apply any clip. So, we should clip using the clip value
+    // 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);
 }