Sk4fLinearGradient fuzzer fixes

gm/gradients.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gm.h"
 #include "SkGradientShader.h"
 #include "SkLinearGradient.h"
@@ skipping 901 matching lines @@
     canvas->drawRect(SkRect::MakeXYWH(0, 0, 500, 500), p);
 }
 
 DEF_SIMPLE_GM(gradient_many_stops, canvas, 500, 500) {
     draw_many_stops(canvas, 0);
 }
 
 DEF_SIMPLE_GM(gradient_many_stops_4f, canvas, 500, 500) {
     draw_many_stops(canvas, SkLinearGradient::kForce4fContext_PrivateFlag);
 }
+
+static void draw_subpixel_gradient(SkCanvas* canvas, uint32_t flags) {
+    const SkPoint pts[] = { {50, 50}, {50.1f, 50.1f}};
+    SkColor colors[] = { SK_ColorRED, SK_ColorGREEN, SK_ColorBLUE };
+    SkPaint p;
+    p.setShader(SkGradientShader::MakeLinear(
+        pts, colors, nullptr, SK_ARRAY_COUNT(colors), SkShader::kRepeat_TileMode, flags, nullptr));
+    canvas->drawRect(SkRect::MakeXYWH(0, 0, 500, 500), p);
+}
+
+DEF_SIMPLE_GM(gradient_subpixel, canvas, 500, 500) {
+    draw_subpixel_gradient(canvas, 0);
+}
+
+DEF_SIMPLE_GM(gradient_subpixel_4f, canvas, 500, 500) {
+    draw_subpixel_gradient(canvas, SkLinearGradient::kForce4fContext_PrivateFlag);
+}