Chromium Code Reviews
chromiumcodereview-hr@appspot.gserviceaccount.com (chromiumcodereview-hr) | Please choose your nickname with Settings | Help | Chromium Project | Gerrit Changes | Sign out
(4750)

Unified Diff: cc/layer_sorter.cc

Issue 11362024: added fix that deals with precision in layer sorter (Closed) Base URL: svn://svn.chromium.org/chrome/trunk/src
Patch Set: updated to tip of tree Created 8 years, 1 month ago
Use n/p to move between diff chunks; N/P to move between comments. Draft comments are only viewable by you.
Jump to:
View side-by-side diff with in-line comments
Download patch
« no previous file with comments | « no previous file | cc/layer_sorter_unittest.cc » ('j') | cc/layer_sorter_unittest.cc » ('J')
Expand Comments ('e') | Collapse Comments ('c') | Show Comments Hide Comments ('s')
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
« no previous file with comments | « no previous file | cc/layer_sorter_unittest.cc » ('j') | cc/layer_sorter_unittest.cc » ('J')

Powered by Google App Engine
This is Rietveld 408576698