Shifting layer position for sticky element to avoid passing unnessary variable to cc

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMappingTest.cpp

 // 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 "core/layout/compositing/CompositedLayerMapping.h"
 
 #include "core/frame/LocalFrameView.h"
 #include "core/layout/LayoutBoxModelObject.h"
 #include "core/layout/LayoutTestHelper.h"
 #include "core/layout/api/LayoutViewItem.h"
@@ skipping 1477 matching lines @@
       "    <div class='composited container'>"
       "      <div class='innerPadding'></div>"
       "      <div id='sticky' class='composited'></div>"
       "  </div></div></div>");
 
   PaintLayer* sticky_layer =
       ToLayoutBox(GetLayoutObjectByElementId("sticky"))->Layer();
   CompositedLayerMapping* sticky_mapping =
       sticky_layer->GetCompositedLayerMapping();
   ASSERT_TRUE(sticky_mapping);
-  // Main thread offset for sticky should be "StickyTop - InnerPadding".
-  EXPECT_EQ(IntPoint(0, 15), IntPoint(sticky_mapping->MainGraphicsLayer()
-                                          ->ContentLayer()
-                                          ->Layer()
-                                          ->OffsetForStickyPosition()));
 
   // Now scroll the page - this should increase the main thread offset.
   LayoutBoxModelObject* scroller =
       ToLayoutBoxModelObject(GetLayoutObjectByElementId("scroller"));
   PaintLayerScrollableArea* scrollable_area = scroller->GetScrollableArea();
   scrollable_area->ScrollToAbsolutePosition(
       FloatPoint(scrollable_area->ScrollPosition().X(), 100));
   ASSERT_EQ(100.0, scrollable_area->ScrollPosition().Y());
 
   sticky_layer->SetNeedsCompositingInputsUpdate();
   EXPECT_TRUE(sticky_layer->NeedsCompositingInputsUpdate());
   GetDocument().View()->UpdateLifecycleToCompositingCleanPlusScrolling();
   EXPECT_FALSE(sticky_layer->NeedsCompositingInputsUpdate());
-
-  EXPECT_EQ(IntPoint(0, 115), IntPoint(sticky_mapping->MainGraphicsLayer()
-                                           ->ContentLayer()
-                                           ->Layer()
-                                           ->OffsetForStickyPosition()));
 }
 
 TEST_P(CompositedLayerMappingTest, StickyPositionNotSquashed) {
   SetBodyInnerHTML(
       "<style>"
       "#scroller { overflow: auto; height: 200px; }"
       "#sticky1, #sticky2, #sticky3 {position: sticky; top: 0; width: 50px;"
       "    height: 50px; background: rgba(0, 128, 0, 0.5);}"
       "#sticky1 {backface-visibility: hidden;}"
       ".spacer {height: 2000px;}"
@@ skipping 23 matching lines @@
   GetDocument().View()->UpdateAllLifecyclePhases();
 
   // Now that sticky2 and sticky3 overlap sticky1 they will be promoted, but
   // they should not be squashed into the same layer because they scroll with
   // respect to each other.
   EXPECT_EQ(kPaintsIntoOwnBacking, sticky1->GetCompositingState());
   EXPECT_EQ(kPaintsIntoOwnBacking, sticky2->GetCompositingState());
   EXPECT_EQ(kPaintsIntoOwnBacking, sticky3->GetCompositingState());
 }
 
+TEST_P(CompositedLayerMappingTest, LayerPositionForStickyElement) {
+  SetBodyInnerHTML(
+      "<style>"
+      " .scroller { overflow: scroll; width: 200px; height: 600px; }"
+      " .composited { will-change:transform; }"
+      " .box { position: sticky; width: 185px; height: 50px; top: 0px; }"
+      " .container { width: 100%; height: 1000px; }"
+      "</style>"
+      "<div id='scroller' class='composited scroller'>"
+      " <div class='container'>"
+      "  <div id='sticky' class='box'></div>"
+      " </div>"
+      "</div>");
+
+  CompositedLayerMapping* mapping =
+      ToLayoutBlock(GetLayoutObjectByElementId("sticky"))
+          ->Layer()
+          ->GetCompositedLayerMapping();
+  ASSERT_TRUE(mapping);
+  GraphicsLayer* main_graphics_layer = mapping->MainGraphicsLayer();
+
+  PaintLayer* scroller =
+      ToLayoutBlock(GetLayoutObjectByElementId("scroller"))->Layer();
+  PaintLayerScrollableArea* scrollable_area = scroller->GetScrollableArea();
+  scrollable_area->ScrollToAbsolutePosition(
+      FloatPoint(scrollable_area->ScrollPosition().Y(), 100));
+  GetDocument().View()->UpdateAllLifecyclePhases();
+
+  EXPECT_FLOAT_EQ(0, main_graphics_layer->GetPosition().X());
+  EXPECT_FLOAT_EQ(0, main_graphics_layer->GetPosition().Y());

[flackr, 2017/06/08 18:56:19]

You should have both a composited scroller and non composited scroller test
since these have different layer positions.

[yigu, 2017/06/08 23:30:03]

I added a test with non-composited scroller. As the scroller doesn't need
composited scrolling we don't compute the local sticky offset as we do in the
other test. The layer position is therefore not affected.

[flackr, 2017/06/08 23:54:46]

All else being equal, one test should have the sticky offset subtracted off of
the layer position and the other not (i.e. these two tests should exercise both
code branches, the one you added and the existing one).

+}
+
 }  // namespace blink