Ensure the Gaussian tail of circle blurs goes to zero.

Compare blurcircle GM masked so that values <255 are white and =255 are black:
https://x20web.corp.google.com/~benjaminwagner/review/1723383002/blurcircles-lt255-before.png
https://x20web.corp.google.com/~benjaminwagner/review/1723383002/blurcircles-lt255-after.png

This is a spinoff of https://codereview.chromium.org/1691403002, which was previously causing more "rectangles" in this GM.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1723383002

Review URL: https://codereview.chromium.org/1723383002

1 files changed, 3 insertions, 1 deletions

diff --git a/src/effects/GrCircleBlurFragmentProcessor.cpp b/src/effects/GrCircleBlurFragmentProcessor.cpp
index f319e3d90f..39e3947049 100644
--- a/src/effects/GrCircleBlurFragmentProcessor.cpp
+++ b/src/effects/GrCircleBlurFragmentProcessor.cpp
@@ -209,9 +209,11 @@ static uint8_t* create_profile(float halfWH, float sigma) {
     compute_profile_offset_and_size(halfWH, sigma, &offset, &numSteps);
 
     uint8_t* weights = new uint8_t[numSteps];
-    for (int i = 0; i < numSteps; ++i) {
+    for (int i = 0; i < numSteps - 1; ++i) {
         weights[i] = eval_at(offset+i, halfWH, halfKernel.get(), kernelWH);
     }
+    // Ensure the tail of the Gaussian goes to zero.
+    weights[numSteps-1] = 0;
 
     return weights;
 }