cc : Use dynamically calculated target space transforms

cc/trees/property_tree.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stddef.h>
 
 #include <set>
 #include <vector>
 
 #include "base/logging.h"
@@ skipping 1968 matching lines @@
                                  1.0 / effect_node->surface_contents_scale.y());
   return screen_space_transform;
 }
 
 bool PropertyTrees::ComputeTransformToTarget(int transform_id,
                                              int effect_id,
                                              gfx::Transform* transform) const {
   transform->MakeIdentity();
 
   int target_transform_id;
+  const EffectNode* effect_node = effect_tree.Node(effect_id);
   if (effect_id == EffectTree::kInvalidNodeId) {
     // This can happen when PaintArtifactCompositor builds property trees as
     // it doesn't set effect ids on clip nodes. We want to compute transform
     // to the root in this case.
     target_transform_id = TransformTree::kRootNodeId;
   } else {
-    const EffectNode* effect_node = effect_tree.Node(effect_id);
     DCHECK(effect_node->has_render_surface ||
            effect_node->id == EffectTree::kRootNodeId);
     target_transform_id = effect_node->transform_id;
   }
 
-  return transform_tree.ComputeTransform(transform_id, target_transform_id,
-                                         transform);
+  if (!verify_transform_tree_calculations || transform_id < target_transform_id)
+    return transform_tree.ComputeTransform(transform_id, target_transform_id,
+                                           transform);
+  transform->ConcatTransform(
+      GetDrawTransforms(transform_id, effect_id).to_target);
+  if (effect_node->surface_contents_scale.x() != 0.f &&
+      effect_node->surface_contents_scale.y() != 0.f)
+    transform->matrix().postScale(
+        1.0f / effect_node->surface_contents_scale.x(),
+        1.0f / effect_node->surface_contents_scale.y(), 1.0f);
+#if DCHECK_IS_ON()
+  gfx::Transform expected;
+  transform_tree.ComputeTransform(transform_id, target_transform_id, &expected);
+  DCHECK(expected.ApproximatelyEqual(*transform));

[ajuma, 2016/07/29 18:03:18]

Since this has a relatively large tolerance for errors in the translation
component (it lets them be off by 1), I'd rather that the returned |transform|
be the value computed the old way, since that's still what is used outside of
tests (to avoid situations where we accidentally introduce an off-by-1 error in
the non-test code but have no test coverage to catch it).

[jaydasika, 2016/07/29 18:20:16]

Done.

+#endif
+  return true;
 }
 
 bool PropertyTrees::ComputeTransformFromTarget(
     int transform_id,
     int effect_id,
     gfx::Transform* transform) const {
   transform->MakeIdentity();
 
   int target_transform_id;
+  const EffectNode* effect_node = effect_tree.Node(effect_id);
   if (effect_id == EffectTree::kInvalidNodeId) {
     // This can happen when PaintArtifactCompositor builds property trees as
     // it doesn't set effect ids on clip nodes. We want to compute transform
     // to the root in this case.
     target_transform_id = TransformTree::kRootNodeId;
   } else {
-    const EffectNode* effect_node = effect_tree.Node(effect_id);
     DCHECK(effect_node->has_render_surface ||
            effect_node->id == EffectTree::kRootNodeId);
     target_transform_id = effect_node->transform_id;
   }
 
-  return transform_tree.ComputeTransform(target_transform_id, transform_id,
-                                         transform);
+  if (!verify_transform_tree_calculations || transform_id > target_transform_id)
+    return transform_tree.ComputeTransform(target_transform_id, transform_id,
+                                           transform);
+
+  auto draw_transforms = GetDrawTransforms(transform_id, effect_id);
+  transform->ConcatTransform(draw_transforms.from_target);
+  transform->Scale(effect_node->surface_contents_scale.x(),
+                   effect_node->surface_contents_scale.y());

[ajuma, 2016/07/29 18:03:18]

Same comment here about setting |transform| to the value computed the old way.

[jaydasika, 2016/07/29 18:20:16]

Done.

+#if DCHECK_IS_ON()
+  gfx::Transform expected;
+  transform_tree.ComputeTransform(target_transform_id, transform_id, &expected);
+  DCHECK(expected.ApproximatelyEqual(*transform) ||
+         !draw_transforms.invertible);
+#endif
+  return draw_transforms.invertible;
 }
 
 }  // namespace cc