Remove TransformTree::ComputeTranslation

This code became unused after https://crrev.com/691020.

Change-Id: I9f91a36e98518ec907f63c7cfefc0503481e784b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1846338
Auto-Submit: Philip Rogers <pdr@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703758}

cc/trees/property_tree.cc

@@ -12,7 +12,6 @@
 #include "base/memory/ptr_util.h"
 #include "base/numerics/checked_math.h"
 #include "base/trace_event/traced_value.h"
-#include "cc/layers/layer_impl.h"
 #include "cc/trees/clip_node.h"
 #include "cc/trees/effect_node.h"
 #include "cc/trees/layer_tree_impl.h"
@@ -132,47 +131,6 @@ void TransformTree::set_needs_update(bool needs_update) {
   PropertyTree<TransformNode>::set_needs_update(needs_update);
 }
 
-bool TransformTree::ComputeTranslation(int source_id,
-                                       int dest_id,
-                                       gfx::Transform* transform) const {
-  transform->MakeIdentity();
-  if (source_id == dest_id)
-    return true;
-
-  const TransformNode* dest = Node(dest_id);
-  if (!dest->ancestors_are_invertible)
-    return false;
-  if (source_id != kInvalidNodeId)
-    transform->ConcatTransform(ToScreen(source_id));
-  if (dest_id != kInvalidNodeId) {
-    if (dest->local.IsFlat() && (dest->node_and_ancestors_are_flat ||
-                                 dest->flattens_inherited_transform)) {
-      // In this case, flattenning will not affect the result, so we can use the
-      // FromScreen transform of the dest node.
-      transform->ConcatTransform(FromScreen(dest_id));
-    } else {
-      // In this case, some node between source and destination flattens
-      // inherited transform. Consider the tree R->A->B->C->D, where D is the
-      // source, A is the destination and C flattens inherited transform. The
-      // expected result is D * C * flattened(B). D's ToScreen will be D * C *
-      // flattened(B * A * R), but as the source to destination transform is
-      // at most translation, C and B cannot be non-flat and so flattened(B * A
-      // * R) = B * flattened(A * R). So, to get the expected result we have to
-      // multiply D's ToScreen transform with flattened(A * R)^{-1}, which is
-      // the inverse of flattened ToScreen of destination.
-      gfx::Transform to_screen = ToScreen(dest_id);
-      to_screen.FlattenTo2d();
-      gfx::Transform from_screen;
-      bool success = to_screen.GetInverse(&from_screen);
-      if (!success)
-        return false;
-      transform->ConcatTransform(from_screen);
-    }
-  }
-
-  return true;
-}
-
 TransformNode* TransformTree::FindNodeFromElementId(ElementId id) {
   auto iterator = property_trees()->element_id_to_transform_node_index.find(id);
   if (iterator == property_trees()->element_id_to_transform_node_index.end())

cc/trees/property_tree.h

@@ -137,16 +137,6 @@ class CC_EXPORT TransformTree final : public PropertyTree<TransformNode> {
   TransformNode* FindNodeFromElementId(ElementId id);
   bool OnTransformAnimated(ElementId element_id,
                            const gfx::Transform& transform);
-  // Computes the change of basis transform from node |source_id| to |dest_id|.
-  // This is used by scroll children to compute transform from their scroll
-  // parent space (source) to their parent space (destination) and it can atmost
-  // be a translation. This function assumes that the path from source to
-  // destination has only translations. So, it should not be called when there
-  // can be intermediate 3d transforms but the end result is a translation.
-  bool ComputeTranslation(int source_id,
-                          int dest_id,
-                          gfx::Transform* transform) const;
-
   void ResetChangeTracking();
   // Updates the parent, target, and screen space transforms and snapping.
   void UpdateTransforms(int id);