change composeshader_alpha to exercise srcover as well

gm/composeshader.cpp

Index: gm/composeshader.cpp
diff --git a/gm/composeshader.cpp b/gm/composeshader.cpp
index b5607d511b9bcf92704ef1eb212a0f87990b2ead..9fdcb74369566e89e83bbe4ebd9f2d371004dcad 100644
--- a/gm/composeshader.cpp
+++ b/gm/composeshader.cpp
@@ -15,32 +15,33 @@
 #include "SkString.h"
 #include "SkXfermode.h"
 
+static SkShader* make_shader(SkXfermode::Mode mode) {
+    SkPoint pts[2];
+    SkColor colors[2];
+    
+    pts[0].set(0, 0);
+    pts[1].set(SkIntToScalar(100), 0);
+    colors[0] = SK_ColorRED;
+    colors[1] = SK_ColorBLUE;
+    SkAutoTUnref<SkShader> shaderA(SkGradientShader::CreateLinear(pts, colors, NULL, 2,
+                                                                  SkShader::kClamp_TileMode));
+    
+    pts[0].set(0, 0);
+    pts[1].set(0, SkIntToScalar(100));
+    colors[0] = SK_ColorBLACK;
+    colors[1] = SkColorSetARGB(0x80, 0, 0, 0);
+    SkAutoTUnref<SkShader> shaderB(SkGradientShader::CreateLinear(pts, colors, NULL, 2,
+                                                                  SkShader::kClamp_TileMode));
+    
+    SkAutoTUnref<SkXfermode> xfer(SkXfermode::Create(mode));
+    
+    return SkNEW_ARGS(SkComposeShader, (shaderA, shaderB, xfer));
+}
+
 class ComposeShaderGM : public skiagm::GM {
 public:
     ComposeShaderGM() {
-        SkPoint pts[2];
-        SkColor colors[2];
-
-        pts[0].set(0, 0);
-        pts[1].set(SkIntToScalar(100), 0);
-        colors[0] = SK_ColorRED;
-        colors[1] = SK_ColorBLUE;
-        SkShader* shaderA = SkGradientShader::CreateLinear(pts, colors, NULL, 2,
-                                                           SkShader::kClamp_TileMode);
-
-        pts[0].set(0, 0);
-        pts[1].set(0, SkIntToScalar(100));
-        colors[0] = SK_ColorBLACK;
-        colors[1] = SkColorSetARGB(0x80, 0, 0, 0);
-        SkShader* shaderB = SkGradientShader::CreateLinear(pts, colors, NULL, 2,
-                                                           SkShader::kClamp_TileMode);
-
-        SkXfermode* mode = SkXfermode::Create(SkXfermode::kDstIn_Mode);
-
-        fShader = new SkComposeShader(shaderA, shaderB, mode);
-        shaderA->unref();
-        shaderB->unref();
-        mode->unref();
+        fShader = make_shader(SkXfermode::kDstIn_Mode);
     }
 
     virtual ~ComposeShaderGM() {
@@ -77,7 +78,7 @@ private:
     typedef GM INHERITED ;
 };
 
-class ComposeShaderAlphaGM : public ComposeShaderGM {
+class ComposeShaderAlphaGM : public skiagm::GM {
 public:
     ComposeShaderAlphaGM() {}
 
@@ -87,24 +88,35 @@ protected:
     }
     
     virtual SkISize onISize() SK_OVERRIDE {
-        return SkISize::Make(120, 1024);
+        return SkISize::Make(220, 750);
     }
     
     virtual void onDraw(SkCanvas* canvas) SK_OVERRIDE {
+        SkAutoTUnref<SkShader> shader0(make_shader(SkXfermode::kDstIn_Mode));
+        SkAutoTUnref<SkShader> shader1(make_shader(SkXfermode::kSrcOver_Mode));
+        SkShader* shaders[] = { shader0.get(), shader1.get() };
+
         SkPaint paint;
         paint.setColor(SK_ColorGREEN);
         
         const SkRect r = SkRect::MakeXYWH(5, 5, 100, 100);
-        for (int alpha = 0xFF; alpha > 0; alpha -= 0x20) {
-            paint.setAlpha(0xFF);
-            paint.setShader(NULL);
-            canvas->drawRect(r, paint);
-            
-            paint.setAlpha(alpha);
-            paint.setShader(fShader);
-            canvas->drawRect(r, paint);
-            
-            canvas->translate(r.width() + 5, 0);
+        
+        for (size_t y = 0; y < SK_ARRAY_COUNT(shaders); ++y) {
+            SkShader* shader = shaders[y];
+            canvas->save();
+            for (int alpha = 0xFF; alpha > 0; alpha -= 0x28) {
+                paint.setAlpha(0xFF);
+                paint.setShader(NULL);
+                canvas->drawRect(r, paint);
+                
+                paint.setAlpha(alpha);
+                paint.setShader(shader);
+                canvas->drawRect(r, paint);
+                
+                canvas->translate(r.width() + 5, 0);
+            }
+            canvas->restore();
+            canvas->translate(0, r.height() + 5);
         }
     }
 };