[Reland] Fix SkTwoPointConicalGradient zero-radius handling

r == 0 is within valid gradient range, we shouldn't skip it.

BUG=skia:5023
R=caryclark@google.com,reed@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1756573002

Committed: https://skia.googlesource.com/skia/+/9c0b02a557e9be663a0eb07519e1b6a61a6c3df2

Review URL: https://codereview.chromium.org/1756573002

2 files changed, 6 insertions, 4 deletions

diff --git a/src/effects/gradients/SkGradientShader.cpp b/src/effects/gradients/SkGradientShader.cpp
index 5444c1caad..985d45966b 100644
--- a/src/effects/gradients/SkGradientShader.cpp
+++ b/src/effects/gradients/SkGradientShader.cpp
@@ -840,8 +840,10 @@ SkShader* SkGradientShader::CreateTwoPointConical(const SkPoint& start,
     if (!valid_grad(colors, pos, colorCount, mode)) {
         return nullptr;
     }
-    if (start == end && startRadius == endRadius) {
-        return SkShader::CreateEmptyShader();
+    if (startRadius == endRadius) {
+        if (start == end || startRadius == 0) {
+            return SkShader::CreateEmptyShader();
+        }
     }
 
     EXPAND_1_COLOR(colorCount);
diff --git a/src/effects/gradients/SkTwoPointConicalGradient.cpp b/src/effects/gradients/SkTwoPointConicalGradient.cpp
index b938ebdec7..2209306fe3 100644
--- a/src/effects/gradients/SkTwoPointConicalGradient.cpp
+++ b/src/effects/gradients/SkTwoPointConicalGradient.cpp
@@ -122,10 +122,10 @@ SkFixed TwoPtRadialContext::nextT() {
     // find_quad_roots returns the values sorted, so we start with the last
     float t = roots[countRoots - 1];
     float r = lerp(fRec.fRadius, fRec.fDRadius, t);
-    if (r <= 0) {
+    if (r < 0) {
         t = roots[0];   // might be the same as roots[countRoots-1]
         r = lerp(fRec.fRadius, fRec.fDRadius, t);
-        if (r <= 0) {
+        if (r < 0) {
             return TwoPtRadial::kDontDrawT;
         }
     }