Split radial_gradients2 GM into two to reproduce its bug.

gm/gradients.cpp

Index: gm/gradients.cpp
diff --git a/gm/gradients.cpp b/gm/gradients.cpp
index 9438c33bdc166d38391bb4c1ddcc7a9aacdedc78..e7964fc9ecceba24fcff483545861263400cc3e4 100644
--- a/gm/gradients.cpp
+++ b/gm/gradients.cpp
@@ -363,10 +363,13 @@ private:
 
 class RadialGradient2GM : public GM {
 public:
-    RadialGradient2GM() {}
+    explicit RadialGradient2GM(bool premulFirst) : fPremulFirst(premulFirst) {}
 
 protected:
-    SkString onShortName() { return SkString("radial_gradient2"); }
+    SkString onShortName() {
+        return SkString(fPremulFirst ? "radial_gradient2_premul_then_interp"
+                                     : "radial_gradient2_interp_then_premul");
+    }
     virtual SkISize onISize() { return make_isize(400, 400); }
     void drawBG(SkCanvas* canvas) {
         canvas->drawColor(0xFF000000);
@@ -388,17 +391,24 @@ protected:
         SkPoint center;
         center.set(cx, cy);
 
+        // We can either interpolate endpoints and premultiply each point (default, more precision),
+        // or premultiply the endpoints first, avoiding the need to premultiply each point (cheap).
+        const uint32_t flags = fPremulFirst ? SkGradientShader::kInterpolateColorsInPremul_Flag : 0;
+
         SkAutoTUnref<SkShader> sweep(
                 SkGradientShader::CreateSweep(cx, cy, sweep_colors,
-                                              NULL, SK_ARRAY_COUNT(sweep_colors)));
+                                              NULL, SK_ARRAY_COUNT(sweep_colors),
+                                              NULL, flags));
         SkAutoTUnref<SkShader> radial1(
                 SkGradientShader::CreateRadial(center, radius, colors1,
                                                NULL, SK_ARRAY_COUNT(colors1),
-                                               SkShader::kClamp_TileMode));
+                                               SkShader::kClamp_TileMode,
+                                               NULL, flags));
         SkAutoTUnref<SkShader> radial2(
                 SkGradientShader::CreateRadial(center, radius, colors2,
                                                NULL, SK_ARRAY_COUNT(colors2),
-                                               SkShader::kClamp_TileMode));
+                                               SkShader::kClamp_TileMode,
+                                               NULL, flags));
         paint1.setShader(sweep);
         paint2.setShader(radial1);
         paint3.setShader(radial2);
@@ -409,6 +419,7 @@ protected:
     }
 
 private:
+    bool fPremulFirst;
     typedef GM INHERITED;
 };
 
@@ -432,6 +443,9 @@ static GMRegistry reg5(MyFactory5);
 static GM* MyFactory6(void*) { return new GradientsViewPerspectiveGM; }
 static GMRegistry reg6(MyFactory6);
 
-static GM* MyFactory7(void*) { return new RadialGradient2GM; }
+static GM* MyFactory7(void*) { return new RadialGradient2GM(true); }

[reed1, 2013/09/11 14:33:27]

nitties:

1. If we're going to have 2 gms, might be slightly clearer if we just pass the
"flags" for the gradient as a param, rather than a bool which we happen to know
translates into diff flags.

2. Can we instead change the curr GM to just draw twice on screen, so we can see
at a glance the two different effects side-by-side?

questions, not demands

 static GMRegistry reg7(MyFactory7);
+
+static GM* MyFactory8(void*) { return new RadialGradient2GM(false); }
+static GMRegistry reg8(MyFactory8);
 }