commit 6df2c8e8e030a3be9b3c1bb0436bb39d632df007
author robertphillips <robertphillips@google.com> Mon Oct 03 08:41:04 2016 -0700
committer Commit bot <commit-bot@chromium.org> Mon Oct 03 08:41:04 2016 -0700
tree 0dbaca0de7a9bc74695e5677d5e1bec17ff2a5eb
parent 497630a2af7569d4c6c0f6df0b232f5e0196a8a5

Fix precision issues in SkRRectsGaussianEdgeShader.cpp

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2383863002

Review-Url: https://codereview.chromium.org/2383863002

src/effects/SkRRectsGaussianEdgeShader.cpp

diff --git a/src/effects/SkRRectsGaussianEdgeShader.cpp b/src/effects/SkRRectsGaussianEdgeShader.cpp
index 25c57cd..e7703f9 100644
--- a/src/effects/SkRRectsGaussianEdgeShader.cpp
+++ b/src/effects/SkRRectsGaussianEdgeShader.cpp
@@ -117,7 +117,11 @@
 
             switch (mode) {
             case kCircle_Mode:
-                fragBuilder->codeAppendf("%s = clamp((%s.%c - length(delta))/%s, 0.0, 1.0);",
+                // When a shadow circle gets large we can have some precision issues if
+                // we do "length(delta)/radius". The scaleDist temporary cuts the
+                // delta vector down a bit before invoking length.
+                fragBuilder->codeAppendf("float scaledDist = length(delta/%s);", radName);
+                fragBuilder->codeAppendf("%s = clamp((%s.%c/%s - scaledDist), 0.0, 1.0);",
                                          outputName, sizesName, indices[0], radName);
                 break;
             case kRect_Mode:
@@ -136,7 +140,7 @@
                 // distance from the corner and then use the multiplier to mask
                 // between the two distances.
                 fragBuilder->codeAppendf("float xDist = clamp((%s.%c - abs(delta.x))/%s,"
-                                                             " 0.0, 1.0);",
+                                                             "0.0, 1.0);",
                                          sizesName, indices[0], radName);
                 fragBuilder->codeAppendf("float yDist = clamp((%s.%c - abs(delta.y))/%s,"
                                                              "0.0, 1.0);",