[Reland] Fix SkTwoPointConicalGradient zero-radius handling

tests/GradientTest.cpp

Index: tests/GradientTest.cpp
diff --git a/tests/GradientTest.cpp b/tests/GradientTest.cpp
index 6a277d520efa64d51b654d853cf0297bff95ac31..cc94cbaf7591d3e7ecbca31cfc3422754854d55b 100644
--- a/tests/GradientTest.cpp
+++ b/tests/GradientTest.cpp
@@ -6,6 +6,7 @@
  */
 
 #include "SkCanvas.h"
+#include "SkColorPriv.h"
 #include "SkColorShader.h"
 #include "SkGradientShader.h"
 #include "SkShader.h"
@@ -233,10 +234,33 @@ static void test_linear_fuzz(skiatest::Reporter* reporter) {
     surface->getCanvas()->drawRect(r, paint);
 }
 
+// https://bugs.chromium.org/p/skia/issues/detail?id=5023
+// We should still shade pixels for which the radius is exactly 0.
+static void test_two_point_conical_zero_radius(skiatest::Reporter* reporter) {
+    SkAutoTUnref<SkSurface> surface(SkSurface::NewRasterN32Premul(5, 5));
+    surface->getCanvas()->clear(SK_ColorRED);
+
+    const SkColor colors[] = { SK_ColorGREEN, SK_ColorBLUE };
+    SkAutoTUnref<SkShader> shader(SkGradientShader::CreateTwoPointConical(
+        SkPoint::Make(2.5f, 2.5f), 0,
+        SkPoint::Make(3.0f, 3.0f), 10,
+        colors, nullptr, SK_ARRAY_COUNT(colors), SkShader::kClamp_TileMode));
+    SkPaint p;
+    p.setShader(shader);
+    surface->getCanvas()->drawPaint(p);
+
+    // r == 0 for the center pixel.
+    // verify that we draw it (no red bleed)
+    SkPMColor centerPMColor;
+    surface->readPixels(SkImageInfo::MakeN32Premul(1, 1), &centerPMColor, sizeof(SkPMColor), 2, 2);
+    REPORTER_ASSERT(reporter, SkGetPackedR32(centerPMColor) == 0);
+}
+
 DEF_TEST(Gradient, reporter) {
     TestGradientShaders(reporter);
     TestConstantGradient(reporter);
     test_big_grad(reporter);
     test_nearly_vertical(reporter);
     test_linear_fuzz(reporter);
+    test_two_point_conical_zero_radius(reporter);
 }