Index: cc/layer_sorter.cc |
diff --git a/cc/layer_sorter.cc b/cc/layer_sorter.cc |
index e251e11dc5e8d9764bf5997e6233d01a6b5c5667..ece0afb41fa6b0c9b3b7bec71fce1221864d0f70 100644 |
--- a/cc/layer_sorter.cc |
+++ b/cc/layer_sorter.cc |
@@ -20,6 +20,13 @@ using WebKit::WebTransformationMatrix; |
namespace cc { |
+// This epsilon is used to determine if two layers are too close to each other |
+// to be able to tell which is in front of the other. It's a relative epsilon |
+// so it is robust to changes in scene scale. This value was chosen by picking |
+// a value near machine epsilon and then increasing it until the flickering on |
+// the test scene went away. |
+const float LAYER_EPSILON = 1e-4f; |
enne (OOO)
2012/11/01 22:55:23
style nit: kLayerEpsilon
|
+ |
inline static float perpProduct(const gfx::Vector2dF& u, const gfx::Vector2dF& v) |
{ |
return u.x() * v.y() - u.y() * v.x(); |
@@ -114,10 +121,28 @@ LayerSorter::ABCompareResult LayerSorter::checkOverlap(LayerShape* a, LayerShape |
// which layer is in front. |
float maxPositive = 0; |
float maxNegative = 0; |
+ |
+ // This flag tracks the existance of a numerically accurate seperation |
+ // between two layers. If there is no accurate seperation, the layers |
+ // cannot be effectively sorted. |
+ bool accurate = false; |
shawnsingh
2012/11/01 23:03:57
Could we move the computation of "accurate" and as
|
+ |
for (unsigned o = 0; o < overlapPoints.size(); o++) { |
float za = a->layerZFromProjectedPoint(overlapPoints[o]); |
float zb = b->layerZFromProjectedPoint(overlapPoints[o]); |
+ // Here we attempt to avoid numeric issues with layers that are too |
+ // close together. If we have 2-sided quads that are very close |
+ // together then we will draw them in document order to avoid |
+ // flickering. The correct solution is for the content maker to turn |
+ // on back-face culling or move the quads apart (if they're not two |
+ // sides of one object). |
+ float absDif = fabsf(zb - za); |
+ float absMax = fmax(fabs(zb), fabs(za)); |
shawnsingh
2012/11/01 23:03:57
We probably should be consistent in our usage of f
danakj
2012/11/01 23:06:34
Why aren't we using std::abs() from <cmath> ?
|
+ // Check to see if we've got a result with a reasonable amount of error. |
+ if (absDif > LAYER_EPSILON * absMax) |
shawnsingh
2012/11/01 23:03:57
I'm still not understanding exactly how this check
|
+ accurate = true; |
+ |
float diff = za - zb; |
if (diff > maxPositive) |
maxPositive = diff; |
@@ -125,6 +150,10 @@ LayerSorter::ABCompareResult LayerSorter::checkOverlap(LayerShape* a, LayerShape |
maxNegative = diff; |
} |
+ // If we can't tell which should come first, we use document order. |
+ if (!accurate) |
+ return ABeforeB; |
+ |
float maxDiff = (fabsf(maxPositive) > fabsf(maxNegative) ? maxPositive : maxNegative); |
// If the results are inconsistent (and the z difference substantial to rule out |