Fixed position layer counter-scroll with main thread scroll offset fractional part

cc/layers/layer.cc

 // Copyright 2010 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 "cc/layers/layer.h"
 
 #include <algorithm>
 
 #include "base/atomic_sequence_num.h"
 #include "base/debug/trace_event.h"
@@ skipping 654 matching lines @@
 
 void Layer::SetScrollOffset(const gfx::ScrollOffset& scroll_offset) {
   DCHECK(IsPropertyChangeAllowed());
 
   if (scroll_offset_ == scroll_offset)
     return;
   scroll_offset_ = scroll_offset;
   SetNeedsCommit();
 }
 
+void Layer::SetScrollOffsetFractionalPart(

[aelias_OOO_until_Jul13, 2015/01/28 22:34:16]

Let's not mutate scroll_offset_ in this method.  We can just do something very
simple here:

void Layer::SetScrollOffsetFractionalPart(...) {
  if (scroll_offset_fractional_part_ == scroll_offset_fractional_part)
    return;
  scroll_offset_fractional_part_ = scroll_offset_fractional_part;
  SetNeedsCommit();
}

gfx::Vector2dF Layer::MainScrollOffsetFractionalPart() const {
  return scroll_offset_fractional_part_;
}

[Yufeng Shen (Slow to review), 2015/01/28 22:49:27]

Done.

+    const gfx::Vector2dF& scroll_offset_fractional_part) {
+  gfx::ScrollOffset floored_scroll_offset(
+      gfx::ScrollOffsetToFlooredVector2d(scroll_offset_));
+  gfx::ScrollOffset new_scroll_offset =
+      ScrollOffsetWithDelta(floored_scroll_offset,
+                            scroll_offset_fractional_part);
+  if (new_scroll_offset == scroll_offset_)
+    return;
+  scroll_offset_ = new_scroll_offset;
+  SetNeedsCommit();
+}
+
+gfx::Vector2dF Layer::MainScrollOffsetFractionalPart() const {
+  return scroll_offset_.DeltaFrom(gfx::ScrollOffset(
+      gfx::ScrollOffsetToFlooredVector2d(scroll_offset_)));
+}
+
 void Layer::SetScrollOffsetFromImplSide(
     const gfx::ScrollOffset& scroll_offset) {
   DCHECK(IsPropertyChangeAllowed());
   // This function only gets called during a BeginMainFrame, so there
   // is no need to call SetNeedsUpdate here.
   DCHECK(layer_tree_host_ && layer_tree_host_->CommitRequested());
   if (scroll_offset_ == scroll_offset)
     return;
   scroll_offset_ = scroll_offset;
   SetNeedsPushProperties();
@@ skipping 289 matching lines @@
   } else {
     if (layer_animation_controller_
             ->scroll_offset_animation_was_interrupted()) {
       layer->SetScrollOffsetAndDelta(scroll_offset_, gfx::Vector2dF());
     } else {
       layer->SetScrollOffsetAndDelta(
           scroll_offset_, layer->ScrollDelta() - layer->sent_scroll_delta());
     }
     layer->SetSentScrollDelta(gfx::Vector2dF());
   }
+  layer->SetMainScrollOffsetFractionalPart(MainScrollOffsetFractionalPart());
 
   // Wrap the copy_requests_ in a PostTask to the main thread.
   ScopedPtrVector<CopyOutputRequest> main_thread_copy_requests;
   for (ScopedPtrVector<CopyOutputRequest>::iterator it = copy_requests_.begin();
        it != copy_requests_.end();
        ++it) {
     scoped_refptr<base::SingleThreadTaskRunner> main_thread_task_runner =
         layer_tree_host()->proxy()->MainThreadTaskRunner();
     scoped_ptr<CopyOutputRequest> original_request = copy_requests_.take(it);
     const CopyOutputRequest& original_request_ref = *original_request;
@@ skipping 300 matching lines @@
 }
 
 void Layer::SetFrameTimingRequests(
     const std::vector<FrameTimingRequest>& requests) {
   frame_timing_requests_ = requests;
   frame_timing_requests_dirty_ = true;
   SetNeedsCommit();
 }
 
 }  // namespace cc