Add flag to gradients to interpolate colors in premul space. Experimental API to encapsulate the sh…

gm/alphagradients.cpp

+/*
+ * Copyright 2013 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 "SkCanvas.h"
+#include "SkGradientShader.h"
+
+class AlphaGradientsGM : public skiagm::GM {
+public:
+    AlphaGradientsGM() {}
+
+protected:
+    virtual SkString onShortName() SK_OVERRIDE {
+        return SkString("alphagradients");
+    }
+
+    virtual SkISize onISize() SK_OVERRIDE {
+        return SkISize::Make(640, 480);
+    }
+
+    static void draw_grad(SkCanvas* canvas, const SkRect& r,
+                          SkColor c0, SkColor c1, bool doPreMul) {
+        SkColor colors[] = { c0, c1 };
+        SkPoint pts[] = { { r.fLeft, r.fTop }, { r.fRight, r.fBottom } };
+        SkPaint paint;
+        uint32_t flags = doPreMul ? SkGradientShader::kInterpolateColorsInPremul_Flag : 0;
+        SkShader* s = SkGradientShader::CreateLinear(pts, colors, NULL, 2,
+                                                     SkShader::kClamp_TileMode,
+                                                     NULL, flags);
+        paint.setShader(s)->unref();
+        canvas->drawRect(r, paint);
+        
+        paint.setShader(NULL);
+        paint.setStyle(SkPaint::kStroke_Style);
+        canvas->drawRect(r, paint);
+    }
+
+    virtual void onDraw(SkCanvas* canvas) SK_OVERRIDE {
+        static const struct {
+            SkColor fColor0;
+            SkColor fColor1;
+        } gRec[] = {
+            { 0xFFFFFFFF, 0x00000000 },
+            { 0xFFFFFFFF, 0x00FF0000 },
+            { 0xFFFFFFFF, 0x00FFFF00 },
+            { 0xFFFFFFFF, 0x00FFFFFF },
+            { 0xFFFF0000, 0x00000000 },
+            { 0xFFFF0000, 0x00FF0000 },
+            { 0xFFFF0000, 0x00FFFF00 },
+            { 0xFFFF0000, 0x00FFFFFF },
+            { 0xFF0000FF, 0x00000000 },
+            { 0xFF0000FF, 0x00FF0000 },
+            { 0xFF0000FF, 0x00FFFF00 },
+            { 0xFF0000FF, 0x00FFFFFF },
+        };
+    
+        SkRect r = SkRect::MakeWH(300, 30);
+        
+        canvas->translate(10, 10);
+
+        for (int doPreMul = 0; doPreMul <= 1; ++doPreMul) {
+            canvas->save();
+            for (size_t i = 0; i < SK_ARRAY_COUNT(gRec); ++i) {
+                draw_grad(canvas, r, gRec[i].fColor0, gRec[i].fColor1, SkToBool(doPreMul));
+                canvas->translate(0, r.height() + 8);
+            }
+            canvas->restore();
+            canvas->translate(r.width() + 10, 0);
+        }
+    }
+
+    virtual uint32_t onGetFlags() const { return kSkipPipe_Flag; }
+
+private:
+    typedef skiagm::GM INHERITED;
+};
+
+DEF_GM( return SkNEW(AlphaGradientsGM); )