Update from https://crrev.com/316786

cc/trees/property_tree.cc

Index: cc/trees/property_tree.cc
diff --git a/cc/trees/property_tree.cc b/cc/trees/property_tree.cc
index 95c2b5a7730b570330e9d346cf42e8c241799fbf..25d42aad7451c90e13b3eddfa1f38cd86172076a 100644
--- a/cc/trees/property_tree.cc
+++ b/cc/trees/property_tree.cc
@@ -5,6 +5,7 @@
 #include <set>
 
 #include "base/logging.h"
+#include "cc/base/math_util.h"
 #include "cc/trees/property_tree.h"
 
 namespace cc {
@@ -35,11 +36,16 @@ template class PropertyTree<ClipNode>;
 
 TransformNodeData::TransformNodeData()
     : target_id(-1),
+      content_target_id(-1),
+      needs_local_transform_update(true),
       is_invertible(true),
       ancestors_are_invertible(true),
       is_animated(false),
       to_screen_is_animated(false),
-      flattens(false) {
+      flattens(false),
+      scrolls(false),
+      needs_sublayer_scale(false),
+      layer_scale_factor(1.0f) {
 }
 
 TransformNodeData::~TransformNodeData() {
@@ -79,47 +85,18 @@ bool TransformTree::Are2DAxisAligned(int source_id, int dest_id) const {
          transform.Preserves2dAxisAlignment();
 }
 
-void TransformTree::UpdateScreenSpaceTransform(int id) {
-  TransformNode* current_node = Node(id);
-  TransformNode* parent_node = parent(current_node);
-  TransformNode* target_node = Node(current_node->data.target_id);
-
-  if (!parent_node) {
-    current_node->data.to_screen = current_node->data.to_parent;
-    current_node->data.ancestors_are_invertible = true;
-    current_node->data.to_screen_is_animated = false;
-  } else if (parent_node->data.flattens) {
-    // Flattening is tricky. Once a layer is drawn into its render target, it
-    // cannot escape, so we only need to consider transforms between the layer
-    // and its target when flattening (i.e., its draw transform). To compute the
-    // screen space transform when flattening is involved we combine three
-    // transforms, A * B * C, where A is the screen space transform of the
-    // target, B is the flattened draw transform of the layer's parent, and C is
-    // the local transform.
-    current_node->data.to_screen = target_node->data.to_screen;
-    gfx::Transform flattened;
-    ComputeTransform(parent_node->id, target_node->id, &flattened);
-    flattened.FlattenTo2d();
-    current_node->data.to_screen.PreconcatTransform(flattened);
-    current_node->data.to_screen.PreconcatTransform(
-        current_node->data.to_parent);
-    current_node->data.ancestors_are_invertible =
-        parent_node->data.ancestors_are_invertible;
-  } else {
-    current_node->data.to_screen = parent_node->data.to_screen;
-    current_node->data.to_screen.PreconcatTransform(
-        current_node->data.to_parent);
-    current_node->data.ancestors_are_invertible =
-        parent_node->data.ancestors_are_invertible;
-  }
-  if (!current_node->data.to_screen.GetInverse(&current_node->data.from_screen))
-    current_node->data.ancestors_are_invertible = false;
-
-  if (parent_node) {
-    current_node->data.to_screen_is_animated =
-        current_node->data.is_animated ||
-        parent_node->data.to_screen_is_animated;
-  }
+void TransformTree::UpdateTransforms(int id) {
+  TransformNode* node = Node(id);
+  TransformNode* parent_node = parent(node);
+  TransformNode* target_node = Node(node->data.target_id);
+  if (node->data.needs_local_transform_update)
+    UpdateLocalTransform(node);
+  UpdateLocalTransform(node);
+  UpdateScreenSpaceTransform(node, parent_node, target_node);
+  UpdateSublayerScale(node);
+  UpdateTargetSpaceTransform(node, target_node);
+  UpdateIsAnimated(node, parent_node);
+  UpdateSnapping(node);
 }
 
 bool TransformTree::IsDescendant(int desc_id, int source_id) const {
@@ -196,4 +173,123 @@ bool TransformTree::CombineInversesBetween(int source_id,
   return all_are_invertible;
 }
 
+void TransformTree::UpdateLocalTransform(TransformNode* node) {
+  gfx::Transform transform = node->data.post_local;
+  transform.Translate(-node->data.scroll_offset.x(),
+                      -node->data.scroll_offset.y());
+  transform.PreconcatTransform(node->data.local);
+  transform.PreconcatTransform(node->data.pre_local);
+  node->data.set_to_parent(transform);
+  node->data.needs_local_transform_update = false;
+}
+
+void TransformTree::UpdateScreenSpaceTransform(TransformNode* node,
+                                               TransformNode* parent_node,
+                                               TransformNode* target_node) {
+  if (!parent_node) {
+    node->data.to_screen = node->data.to_parent;
+    node->data.ancestors_are_invertible = true;
+    node->data.to_screen_is_animated = false;
+  } else if (parent_node->data.flattens) {
+    // Flattening is tricky. Once a layer is drawn into its render target, it
+    // cannot escape, so we only need to consider transforms between the layer
+    // and its target when flattening (i.e., its draw transform). To compute the
+    // screen space transform when flattening is involved we combine three
+    // transforms, A * B * C, where A is the screen space transform of the
+    // target, B is the flattened draw transform of the layer's parent, and C is
+    // the local transform.
+    node->data.to_screen = target_node->data.to_screen;
+    gfx::Transform flattened;
+    ComputeTransform(parent_node->id, target_node->id, &flattened);
+    flattened.FlattenTo2d();
+    node->data.to_screen.PreconcatTransform(flattened);
+    node->data.to_screen.PreconcatTransform(node->data.to_parent);
+    node->data.ancestors_are_invertible =
+        parent_node->data.ancestors_are_invertible;
+  } else {
+    node->data.to_screen = parent_node->data.to_screen;
+    node->data.to_screen.PreconcatTransform(node->data.to_parent);
+    node->data.ancestors_are_invertible =
+        parent_node->data.ancestors_are_invertible;
+  }
+
+  if (!node->data.to_screen.GetInverse(&node->data.from_screen))
+    node->data.ancestors_are_invertible = false;
+}
+
+void TransformTree::UpdateSublayerScale(TransformNode* node) {
+  // The sublayer scale depends on the screen space transform, so update it too.
+  node->data.sublayer_scale =
+      node->data.needs_sublayer_scale
+          ? MathUtil::ComputeTransform2dScaleComponents(
+                node->data.to_screen, node->data.layer_scale_factor)
+          : gfx::Vector2dF(1.0f, 1.0f);
+}
+
+void TransformTree::UpdateTargetSpaceTransform(TransformNode* node,
+                                               TransformNode* target_node) {
+  node->data.to_target.MakeIdentity();
+  if (node->data.needs_sublayer_scale) {
+    node->data.to_target.Scale(node->data.sublayer_scale.x(),
+                               node->data.sublayer_scale.y());
+  } else {
+    const bool target_is_root_surface = target_node->id == 1;
+    // In order to include the root transform for the root surface, we walk up
+    // to the root of the transform tree in ComputeTransform.
+    int target_id = target_is_root_surface ? 0 : target_node->id;
+    if (target_node) {
+      node->data.to_target.Scale(target_node->data.sublayer_scale.x(),
+                                 target_node->data.sublayer_scale.y());
+    }
+
+    gfx::Transform unscaled_target_transform;
+    ComputeTransform(node->id, target_id, &unscaled_target_transform);
+    node->data.to_target.PreconcatTransform(unscaled_target_transform);
+  }
+
+  if (!node->data.to_target.GetInverse(&node->data.from_target))
+    node->data.ancestors_are_invertible = false;
+}
+
+void TransformTree::UpdateIsAnimated(TransformNode* node,
+                                     TransformNode* parent_node) {
+  if (parent_node) {
+    node->data.to_screen_is_animated =
+        node->data.is_animated || parent_node->data.to_screen_is_animated;
+  }
+}
+
+void TransformTree::UpdateSnapping(TransformNode* node) {
+  if (!node->data.scrolls || node->data.to_screen_is_animated ||
+      !node->data.to_target.IsScaleOrTranslation()) {
+    return;
+  }
+
+  // Scroll snapping must be done in target space (the pixels we care about).
+  // This means we effectively snap the target space transform. If TT is the
+  // target space transform and TT' is TT with its translation components
+  // rounded, then what we're after is the scroll delta X, where TT * X = TT'.
+  // I.e., we want a transform that will realize our scroll snap. It follows
+  // that X = TT^-1 * TT'. We cache TT and TT^-1 to make this more efficient.
+  gfx::Transform rounded = node->data.to_target;
+  rounded.RoundTranslationComponents();
+  gfx::Transform delta = node->data.from_target;
+  delta *= rounded;
+  gfx::Transform inverse_delta(gfx::Transform::kSkipInitialization);
+  bool invertible_delta = delta.GetInverse(&inverse_delta);
+
+  // The delta should be a translation, modulo floating point error, and should
+  // therefore be invertible.
+  DCHECK(invertible_delta);
+
+  // Now that we have our scroll delta, we must apply it to each of our
+  // combined, to/from matrices.
+  node->data.to_parent.PreconcatTransform(delta);
+  node->data.from_parent.ConcatTransform(inverse_delta);
+  node->data.to_target.PreconcatTransform(delta);
+  node->data.from_target.ConcatTransform(inverse_delta);
+  node->data.to_screen.PreconcatTransform(delta);
+  node->data.from_screen.ConcatTransform(inverse_delta);
+}
+
 }  // namespace cc