Snap paint offset paint property to pixel boundaries

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilderTest.cpp

 // Copyright 2015 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/LayoutTestHelper.h"
 #include "core/layout/LayoutTreeAsText.h"
 #include "core/layout/LayoutView.h"
 #include "core/paint/ObjectPaintProperties.h"
 #include "platform/graphics/paint/TransformPaintPropertyNode.h"
 #include "platform/testing/UnitTestHelpers.h"
@@ skipping 900 matching lines @@
         "  <div style='position: relative; top: 100px; left: 100px'>"
         "    <div id='spanner' style='column-span: all; opacity: 0.5; width: 100px; height: 100px;'></div>"
         "  </div>"
         "</div>"
     );
 
     LayoutObject& spanner = *getLayoutObjectByElementId("spanner");
     EXPECT_EQ(LayoutPoint(55, 44), spanner.objectPaintProperties()->localBorderBoxProperties()->paintOffset);
 }
 
+TEST_F(PaintPropertyTreeBuilderTest, PaintOffsetPixelSnapping)
+{
+    setBodyInnerHTML(
+        "<style>"
+        "  * { margin: 0; }"
+        "  div { position: relative; }"
+        "</style>"
+        "<div id='a' style='width: 70px; height: 70px; left: 0.7px; top: 0.7px;'>"
+        "  <div id='b' style='background: red; width: 40px; height: 40px; transform: translateZ(0);'>"
+        "    <div id='c' style='background: white; width: 40px; height: 40px; left: 0.7px; top: 0.7px;'></div>"
+        "  </div>"
+        "</div>"
+    );
+
+    ObjectPaintProperties* bProperties = document().getElementById("b")->layoutObject()->objectPaintProperties();
+    EXPECT_EQ(TransformationMatrix().translate3d(0, 0, 0), bProperties->transform()->matrix());
+    // The paint offset transform should be snapped from (0.7,0.7) to (1,1).
+    EXPECT_EQ(TransformationMatrix().translate(1, 1), bProperties->transform()->parent()->matrix());

[chrishtr, 2016/06/29 23:46:30]

Is there already a unittest for not snapping if there is no transform yet
fractional paintOffset?

[pdr., 2016/06/30 16:03:12]

Added one in PaintOffsetWithBasicPixelSnapping.

[chrishtr, 2016/06/30 16:57:17]

That test still uses a transform. I was asking for one that has no transform yet
has fractional pixel offsets, to demonstrate
that they simply get added together, including integral parts.

+}
+
 } // namespace blink