Don't composite trivial 3D on low-end devices.

Bug: 810544
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: Ieec17582540cf79f4f73bc4221226dbdbf20c2d3
Reviewed-on: https://chromium-review.googlesource.com/909951
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: vmpstr <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#535611}

third_party/WebKit/Source/core/paint/compositing/CompositingReasonFinder.cpp

@@ -13,6 +13,8 @@
 #include "core/page/scrolling/RootScrollerUtil.h"
 #include "core/paint/PaintLayer.h"
 
+#include "public/platform/Platform.h"
+
 namespace blink {
 
 CompositingReasonFinder::CompositingReasonFinder(LayoutView& layout_view)
@@ -136,7 +138,12 @@ bool CompositingReasonFinder::RequiresCompositingForTransform(
   // may have transforms, but the layoutObject may be an inline that doesn't
   // support them.
   return layout_object.HasTransformRelatedProperty() &&
-         layout_object.StyleRef().Has3DTransform();
+         layout_object.StyleRef().Has3DTransform() &&
+         // Don't composite "trivial" 3D transforms such as translateZ(0) on
+         // low-end devices. These devices are much more sensitive to memory
+         // and per-composited-layer commit overhead.
+         (!Platform::Current()->IsLowEndDevice() ||
+          layout_object.StyleRef().Transform().HasNonTrivial3DComponent());
 }
 
 CompositingReasons CompositingReasonFinder::NonStyleDeterminedDirectReasons(

third_party/WebKit/Source/core/paint/compositing/CompositingReasonFinderTest.cpp

@@ -11,6 +11,7 @@
 #include "platform/graphics/GraphicsLayer.h"
 #include "platform/scroll/ScrollTypes.h"
 #include "platform/testing/RuntimeEnabledFeaturesTestHelpers.h"
+#include "platform/testing/TestingPlatformSupport.h"
 
 namespace blink {
 
@@ -26,6 +27,63 @@ class CompositingReasonFinderTest : public RenderingTest {
   }
 };
 
+class CompositingReasonFinderTestPlatform : public TestingPlatformSupport {
+ public:
+  bool IsLowEndDevice() override { return true; }
+};
+
+TEST_F(CompositingReasonFinderTest, DontPromoteTrivial3DLowEnd) {
+  ScopedTestingPlatformSupport<CompositingReasonFinderTestPlatform> platform;
+
+  SetBodyInnerHTML(R"HTML(
+    <div id='target'
+      style='width: 100px; height: 100px; transform: translateZ(0)'></div>
+  )HTML");
+
+  Element* target = GetDocument().getElementById("target");
+  PaintLayer* paint_layer =
+      ToLayoutBoxModelObject(target->GetLayoutObject())->Layer();
+  EXPECT_EQ(kNotComposited, paint_layer->GetCompositingState());
+}
+
+TEST_F(CompositingReasonFinderTest, PromoteNonTrivial3DLowEnd) {
+  ScopedTestingPlatformSupport<CompositingReasonFinderTestPlatform> platform;
+
+  SetBodyInnerHTML(R"HTML(
+    <div id='target'
+      style='width: 100px; height: 100px; transform: translateZ(1px)'></div>
+  )HTML");
+
+  Element* target = GetDocument().getElementById("target");
+  PaintLayer* paint_layer =
+      ToLayoutBoxModelObject(target->GetLayoutObject())->Layer();
+  EXPECT_EQ(kPaintsIntoOwnBacking, paint_layer->GetCompositingState());
+}
+
+TEST_F(CompositingReasonFinderTest, PromoteTrivial3DByDefault) {
+  SetBodyInnerHTML(R"HTML(
+    <div id='target'
+      style='width: 100px; height: 100px; transform: translateZ(0)'></div>
+  )HTML");
+
+  Element* target = GetDocument().getElementById("target");
+  PaintLayer* paint_layer =
+      ToLayoutBoxModelObject(target->GetLayoutObject())->Layer();
+  EXPECT_EQ(kPaintsIntoOwnBacking, paint_layer->GetCompositingState());
+}
+
+TEST_F(CompositingReasonFinderTest, PromoteNonTrivial3DByDefault) {
+  SetBodyInnerHTML(R"HTML(
+    <div id='target'
+      style='width: 100px; height: 100px; transform: translateZ(1px)'></div>
+  )HTML");
+
+  Element* target = GetDocument().getElementById("target");
+  PaintLayer* paint_layer =
+      ToLayoutBoxModelObject(target->GetLayoutObject())->Layer();
+  EXPECT_EQ(kPaintsIntoOwnBacking, paint_layer->GetCompositingState());
+}
+
 TEST_F(CompositingReasonFinderTest, PromoteOpaqueFixedPosition) {
   ScopedCompositeOpaqueFixedPositionForTest composite_fixed_position(true);
 
@@ -40,8 +98,6 @@ TEST_F(CompositingReasonFinderTest, PromoteOpaqueFixedPosition) {
     <div id='spacer' style='height: 2000px'></div>
   )HTML");
 
-  GetDocument().View()->UpdateAllLifecyclePhases();
-
   // The translucent fixed box should not be promoted.
   Element* element = GetDocument().getElementById("translucent");
   PaintLayer* paint_layer =
@@ -74,7 +130,6 @@ TEST_F(CompositingReasonFinderTest, OnlyAnchoredStickyPositionPromoted) {
       <div style='height: 2000px;'></div>
     </div>
   )HTML");
-  GetDocument().View()->UpdateAllLifecyclePhases();
 
   EXPECT_EQ(kPaintsIntoOwnBacking,
             ToLayoutBoxModelObject(GetLayoutObjectByElementId("sticky-top"))
@@ -100,7 +155,6 @@ TEST_F(CompositingReasonFinderTest, OnlyScrollingStickyPositionPromoted) {
       <div id='sticky-no-scrolling' class='sticky'></div>
     </div>
   )HTML");
-  GetDocument().View()->UpdateAllLifecyclePhases();
 
   EXPECT_EQ(
       kPaintsIntoOwnBacking,
@@ -131,7 +185,6 @@ TEST_F(CompositingReasonFinderTest, OnlyNonTransformedFixedLayersPromoted) {
       <div id="spacer"></div>
     </div>
   )HTML");
-  GetDocument().View()->UpdateAllLifecyclePhases();
 
   EXPECT_TRUE(RuntimeEnabledFeatures::CompositeOpaqueScrollersEnabled());
   Element* parent = GetDocument().getElementById("parent");
@@ -181,7 +234,6 @@ TEST_F(CompositingReasonFinderTest, OnlyOpaqueFixedLayersPromoted) {
       <div id="spacer"></div>
     </div>
   )HTML");
-  GetDocument().View()->UpdateAllLifecyclePhases();
 
   EXPECT_TRUE(RuntimeEnabledFeatures::CompositeOpaqueScrollersEnabled());
   Element* parent = GetDocument().getElementById("parent");
@@ -319,7 +371,6 @@ TEST_F(CompositingReasonFinderTest, CompositeNestedSticky) {
       </div>
     </div>
   )HTML");
-  GetDocument().View()->UpdateAllLifecyclePhases();
 
   Element* outer_sticky = GetDocument().getElementById("outerSticky");
   PaintLayer* outer_sticky_layer =

third_party/WebKit/Source/platform/transforms/ScaleTransformOperation.h

@@ -80,6 +80,8 @@ class PLATFORM_EXPORT ScaleTransformOperation final
     return x_ == s->x_ && y_ == s->y_ && z_ == s->z_;
   }
 
+  virtual bool HasNonTrivial3DComponent() const { return z_ != 1.0; }
+
   scoped_refptr<TransformOperation> Zoom(double factor) final { return this; }
 
   ScaleTransformOperation(double sx, double sy, double sz, OperationType type)

third_party/WebKit/Source/platform/transforms/TransformOperation.h

@@ -101,6 +101,8 @@ class PLATFORM_EXPORT TransformOperation
            op_type == kInterpolated;
   }
 
+  virtual bool HasNonTrivial3DComponent() const { return Is3DOperation(); }
+
   virtual bool DependsOnBoxSize() const { return false; }
 };
 

third_party/WebKit/Source/platform/transforms/TransformOperations.h

@@ -49,22 +49,32 @@ class PLATFORM_EXPORT TransformOperations {
   bool operator!=(const TransformOperations& o) const { return !(*this == o); }
 
   void Apply(const FloatSize& sz, TransformationMatrix& t) const {
-    for (unsigned i = 0; i < operations_.size(); ++i)
-      operations_[i]->Apply(t, sz);
+    for (auto& operation : operations_)
+      operation->Apply(t, sz);
   }
 
   // Return true if any of the operation types are 3D operation types (even if
   // the values describe affine transforms)
   bool Has3DOperation() const {
-    for (unsigned i = 0; i < operations_.size(); ++i)
-      if (operations_[i]->Is3DOperation())
+    for (auto& operation : operations_)
+      if (operation->Is3DOperation())
         return true;
     return false;
   }
 
+  // Returns true if any operation has a non-trivial component in the Z
+  // axis.
+  bool HasNonTrivial3DComponent() const {
+    for (auto& operation : operations_) {
+      if (operation->HasNonTrivial3DComponent())
+        return true;
+    }
+    return false;
+  }
+
   bool DependsOnBoxSize() const {
-    for (unsigned i = 0; i < operations_.size(); ++i) {
-      if (operations_[i]->DependsOnBoxSize())
+    for (auto& operation : operations_) {
+      if (operation->DependsOnBoxSize())
         return true;
     }
     return false;

third_party/WebKit/Source/platform/transforms/TranslateTransformOperation.h

@@ -107,6 +107,8 @@ class PLATFORM_EXPORT TranslateTransformOperation final
     DCHECK(IsMatchingOperationType(type));
   }
 
+  bool HasNonTrivial3DComponent() const override { return z_ != 0.0; }
+
   Length x_;
   Length y_;
   double z_;