cc: Correct inverted directions in occlusion tracker background filter logic.

cc/trees/occlusion_tracker_unittest.cc

Index: cc/trees/occlusion_tracker_unittest.cc
diff --git a/cc/trees/occlusion_tracker_unittest.cc b/cc/trees/occlusion_tracker_unittest.cc
index 766df2da1743604e315c5435d482e085e386c88c..539f0a397f7a6c4c2e5304744607c7063915b894 100644
--- a/cc/trees/occlusion_tracker_unittest.cc
+++ b/cc/trees/occlusion_tracker_unittest.cc
@@ -1540,6 +1540,125 @@ class OcclusionTrackerTestDontOccludePixelsNeededForBackgroundFilter
 ALL_OCCLUSIONTRACKER_TEST(
     OcclusionTrackerTestDontOccludePixelsNeededForBackgroundFilter);
 
+class OcclusionTrackerTestDontOccludePixelsNeededForDropShadowBackgroundFilter
+    : public OcclusionTrackerTest {
+ protected:
+  explicit OcclusionTrackerTestDontOccludePixelsNeededForDropShadowBackgroundFilter(
+      bool opaque_layers)
+      : OcclusionTrackerTest(opaque_layers) {}
+  void RunMyTest() override {
+    gfx::Transform scale_by_half;
+    scale_by_half.Scale(0.5, 0.5);
+
+    FilterOperations filters;
+    filters.Append(FilterOperation::CreateDropShadowFilter(gfx::Point(10, 10),
+                                                           5, SK_ColorBLACK));
+
+    enum Direction {
+      LEFT,
+      RIGHT,
+      TOP,
+      BOTTOM,
+      LAST_DIRECTION = BOTTOM,
+    };
+
+    for (int i = 0; i <= LAST_DIRECTION; ++i) {
+      SCOPED_TRACE(i);
+
+      // Make a 50x50 filtered surface that is adjacent to occluding layers
+      // which are above it in the z-order in various configurations. The
+      // surface is scaled to test that the pixel moving is done in the target
+      // space, where the background filter is applied.
+      TestContentLayerImpl* parent = this->CreateRoot(
+          this->identity_matrix, gfx::PointF(), gfx::Size(200, 200));
+      LayerImpl* filtered_surface = this->CreateDrawingLayer(
+          parent, scale_by_half, gfx::PointF(50.f, 50.f), gfx::Size(100, 100),
+          false);
+      filtered_surface->test_properties()->background_filters = filters;
+      gfx::Rect occlusion_rect;
+      switch (i) {
+        case LEFT:
+          occlusion_rect = gfx::Rect(0, 0, 50, 200);
+          break;
+        case RIGHT:
+          occlusion_rect = gfx::Rect(100, 0, 50, 200);

[enne (OOO), 2016/07/06 18:20:30]

Shouldn't an adjacent occlusion layer be (150, 0) 50x200? Since you have a
200x200 root layer and the filtering layer is (50, 50) 100x100?

[jbroman, 2016/07/06 18:42:48]

That would also work. This matches what the test above does.

[enne (OOO), 2016/07/06 19:50:00]

I'm just saying the comment above that this is adjacent doesn't really make
sense here.  I think making it 150 would make the test more understandable. 
What do you think?

[jbroman, 2016/07/06 20:26:06]

Turns out it _is_ adjacent, because it's only 50x50 after the scale. The comment
above tries to explain this, but you and I both missed it, so I'm going to try
and clarify.

+          break;
+        case TOP:
+          occlusion_rect = gfx::Rect(0, 0, 200, 50);
+          break;
+        case BOTTOM:
+          occlusion_rect = gfx::Rect(0, 100, 200, 50);
+          break;
+      }
+
+      LayerImpl* occluding_layer = this->CreateDrawingLayer(
+          parent, this->identity_matrix, gfx::PointF(occlusion_rect.origin()),
+          occlusion_rect.size(), true);
+      occluding_layer->test_properties()->force_render_surface = false;
+      this->CalcDrawEtc(parent);
+
+      TestOcclusionTrackerWithClip occlusion(gfx::Rect(0, 0, 200, 200));
+
+      // This layer occludes pixels directly beside the filtered_surface.
+      // Because filtered surface blends pixels in a radius, it will need to see
+      // some of the pixels (up to radius far) underneath the occluding layers.
+      this->VisitLayer(occluding_layer, &occlusion);
+
+      EXPECT_EQ(occlusion_rect.ToString(),
+                occlusion.occlusion_from_inside_target().ToString());
+      EXPECT_TRUE(occlusion.occlusion_from_outside_target().IsEmpty());
+
+      this->VisitLayer(filtered_surface, &occlusion);
+
+      // The occlusion is used fully inside the surface.
+      gfx::Rect occlusion_inside_surface =
+          occlusion_rect - gfx::Vector2d(50, 50);
+      EXPECT_TRUE(occlusion.occlusion_from_inside_target().IsEmpty());
+      EXPECT_EQ(occlusion_inside_surface.ToString(),
+                occlusion.occlusion_from_outside_target().ToString());
+
+      // The surface has a background filter, so it needs pixels that are
+      // currently considered occluded in order to be drawn. So the pixels it
+      // needs should be removed some the occluded area so that when we get to

[enne (OOO), 2016/07/06 18:20:30]

grammar?

[jbroman, 2016/07/06 18:42:48]

Copied from the previous unit test. Would you like both reworded?

[enne (OOO), 2016/07/06 19:49:59]

Yes, please!

[jbroman, 2016/07/06 20:26:06]

Reworded in a way that's hopefully clearer.

+      // the parent they are drawn.
+      this->VisitContributingSurface(filtered_surface, &occlusion);
+      this->EnterLayer(parent, &occlusion);
+
+      gfx::Rect expected_occlusion;
+      switch (i) {
+        case LEFT:
+          // The right half of the occlusion is close enough to cast a shadow
+          // that would be visible in the background filter. The shadow reaches
+          // 3*5 + 10 = 25 pixels to the right.
+          expected_occlusion = gfx::Rect(0, 0, 25, 200);
+          break;
+        case RIGHT:
+          // The shadow spreads 3*5 - 10 = 5 pixels to the left, so the
+          // occlusion must recede by 5 to account for that.
+          expected_occlusion = gfx::Rect(105, 0, 45, 200);
+          break;
+        case TOP:
+          // Similar to LEFT.
+          expected_occlusion = gfx::Rect(0, 0, 200, 25);
+          break;
+        case BOTTOM:
+          // Similar to RIGHT.
+          expected_occlusion = gfx::Rect(0, 105, 200, 45);
+          break;
+      }
+
+      EXPECT_EQ(expected_occlusion.ToString(),
+                occlusion.occlusion_from_inside_target().ToString());
+      EXPECT_TRUE(occlusion.occlusion_from_outside_target().IsEmpty());
+
+      this->DestroyLayers();
+    }
+  }
+};
+
+ALL_OCCLUSIONTRACKER_TEST(
+    OcclusionTrackerTestDontOccludePixelsNeededForDropShadowBackgroundFilter);
+
 class OcclusionTrackerTestTwoBackgroundFiltersReduceOcclusionTwice
     : public OcclusionTrackerTest {
  protected: