cc : Reland move screen space scale factor to root transform node

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 650 matching lines @@
   bool is_invertible = node->is_invertible;
   // Even when the current node's transform and the parent's screen space
   // transform are invertible, the current node's screen space transform can
   // become uninvertible due to floating-point arithmetic.
   if (!node->ancestors_are_invertible && parent_node->ancestors_are_invertible)
     is_invertible = false;
   node->node_and_ancestors_are_animated_or_invertible =
       node->has_potential_animation || is_invertible;
 }
 
-void TransformTree::SetDeviceTransform(const gfx::Transform& transform,
-                                       gfx::PointF root_position) {
-  gfx::Transform root_post_local = transform;
-  TransformNode* node = Node(1);
-  root_post_local.Scale(node->post_local_scale_factor,
-                        node->post_local_scale_factor);
-  root_post_local.Translate(root_position.x(), root_position.y());
-  if (node->post_local == root_post_local)
-    return;
+void TransformTree::SetRootTransformsAndScales(
+    float device_scale_factor,
+    float page_scale_factor_for_root,
+    const gfx::Transform& device_transform,
+    gfx::PointF root_position) {
+  // If DT is the device transform, DSF is the matrix scaled by (device scale
+  // factor * page scale factor for root), RP is the matrix translated by root's
+  // position,
+  // Let Screen Space Scale(SSS) = scale component of DT*DSF*RP,
+  // then the screen space transform of the root transform node is set to SSS
+  // and the post local transform of the contents root node is set to
+  // SSS^-1*DT*DSF*RP.
+  gfx::Transform transform = device_transform;
+  transform.Scale(device_scale_factor * page_scale_factor_for_root,
+                  device_scale_factor * page_scale_factor_for_root);
+  transform.Translate(root_position.x(), root_position.y());
+  float fallback_value = device_scale_factor * page_scale_factor_for_root;
+  gfx::Vector2dF screen_space_scale =
+      MathUtil::ComputeTransform2dScaleComponents(transform, fallback_value);
+  DCHECK_NE(screen_space_scale.x(), 0.f);
+  DCHECK_NE(screen_space_scale.y(), 0.f);
 
-  node->post_local = root_post_local;
-  node->needs_local_transform_update = true;
+  gfx::Transform root_to_screen;
+  root_to_screen.Scale(screen_space_scale.x(), screen_space_scale.y());
+  gfx::Transform root_from_screen;
+  bool invertible = root_to_screen.GetInverse(&root_from_screen);
+  DCHECK(invertible);
+  SetToScreen(kRootNodeId, root_to_screen);
+  SetFromScreen(kRootNodeId, root_from_screen);
   set_needs_update(true);
+
+  transform.ConcatTransform(root_from_screen);
+  TransformNode* contents_root_node = Node(kContentsRootNodeId);
+  if (contents_root_node->post_local != transform) {
+    contents_root_node->post_local = transform;
+    contents_root_node->needs_local_transform_update = true;
+  }
 }
 
 void TransformTree::SetDeviceTransformScaleFactor(

[weiliangc, 2016/11/02 15:38:21]

Could this function be folded into above function? I assume the device transform
passed in here should be same as device transform in above function?

[jaydasika, 2016/11/02 17:36:55]

Done.

     const gfx::Transform& transform) {
   gfx::Vector2dF device_transform_scale_components =
       MathUtil::ComputeTransform2dScaleComponents(transform, 1.f);
 
   // Not handling the rare case of different x and y device scale.
   device_transform_scale_factor_ =
       std::max(device_transform_scale_components.x(),
                device_transform_scale_components.y());
 }
 
@@ skipping 248 matching lines @@
               transform_node->local.IsBackFaceVisible();
         }
         return;
       }
     }
   }
   node->hidden_by_backface_visibility = false;
 }
 
 void EffectTree::UpdateSurfaceContentsScale(EffectNode* effect_node) {
-  if (!effect_node->has_render_surface ||
-      effect_node->transform_id == kRootNodeId) {
+  if (!effect_node->has_render_surface) {
     effect_node->surface_contents_scale = gfx::Vector2dF(1.0f, 1.0f);
     return;
   }
 
   TransformTree& transform_tree = property_trees()->transform_tree;
   float layer_scale_factor = transform_tree.device_scale_factor() *
                              transform_tree.device_transform_scale_factor();
   TransformNode* transform_node =
       transform_tree.Node(effect_node->transform_id);
   if (transform_node->in_subtree_of_page_scale_layer)
@@ skipping 1204 matching lines @@
   gfx::Transform from_target;
   bool already_computed_inverse = false;
   if (transform_id == dest_id) {
     target_space_transform.Scale(effect_node->surface_contents_scale.x(),
                                  effect_node->surface_contents_scale.y());
     data.transforms.to_valid = true;
     data.transforms.from_valid = false;
   } else if (transform_id > dest_id) {
     transform_tree.CombineTransformsBetween(transform_id, dest_id,
                                             &target_space_transform);
-    if (dest_id != TransformTree::kRootNodeId)
-      target_space_transform.matrix().postScale(
-          effect_node->surface_contents_scale.x(),
-          effect_node->surface_contents_scale.y(), 1.f);
+    target_space_transform.matrix().postScale(
+        effect_node->surface_contents_scale.x(),
+        effect_node->surface_contents_scale.y(), 1.f);
     data.transforms.to_valid = true;
     data.transforms.from_valid = false;
     data.transforms.might_be_invertible = true;
   } else {
     gfx::Transform combined_transform;
     transform_tree.CombineTransformsBetween(dest_id, transform_id,
                                             &combined_transform);
     if (effect_node->surface_contents_scale.x() != 0.f &&
         effect_node->surface_contents_scale.y() != 0.f)
       combined_transform.Scale(1.0f / effect_node->surface_contents_scale.x(),
@@ skipping 54 matching lines @@
 
   const EffectNode* effect_node = effect_tree.Node(effect_id);
 
   bool success = GetFromTarget(transform_id, effect_id, transform);
   transform->Scale(effect_node->surface_contents_scale.x(),
                    effect_node->surface_contents_scale.y());
   return success;
 }
 
 }  // namespace cc