Add GrEffect::updateKnownColorComponents(). It is used to determine whether the output of an effect has a constant output value for r,g,b, or a.

Review URL: https://codereview.appspot.com/7064057

git-svn-id: http://skia.googlecode.com/svn/trunk@7144 2bbb7eff-a529-9590-31e7-b0007b416f81

2 files changed, 12 insertions, 0 deletions

diff --git a/src/effects/gradients/SkGradientShader.cpp b/src/effects/gradients/SkGradientShader.cpp
index 8521bdbf61..7d779708f6 100644
--- a/src/effects/gradients/SkGradientShader.cpp
+++ b/src/effects/gradients/SkGradientShader.cpp
@@ -753,6 +753,8 @@ GrGradientEffect::GrGradientEffect(GrContext* ctx,
     SkBitmap bitmap;
     shader.getGradientTableBitmap(&bitmap);
 
+    fIsOpaque = shader.isOpaque();
+
     GrTextureStripAtlas::Desc desc;
     desc.fWidth  = bitmap.width();
     desc.fHeight = 32;
diff --git a/src/effects/gradients/SkGradientShaderPriv.h b/src/effects/gradients/SkGradientShaderPriv.h
index 552013efa5..b2b8c47a1c 100644
--- a/src/effects/gradients/SkGradientShaderPriv.h
+++ b/src/effects/gradients/SkGradientShaderPriv.h
@@ -243,6 +243,15 @@ public:
                fYCoord == s.getYCoord() && fMatrix.cheapEqualTo(s.getMatrix());
     }
 
+    virtual void getConstantColorComponents(GrColor* color,
+                                            uint32_t* validFlags) const SK_OVERRIDE {
+        if (fIsOpaque && (kA_ValidComponentFlag & *validFlags) && 0xff == GrColorUnpackA(*color)) {
+            *validFlags = kA_ValidComponentFlag;
+        } else {
+            *validFlags = 0;
+        }
+    }
+
 protected:
 
     /** Populates a pair of arrays with colors and stop info to construct a random gradient.
@@ -264,6 +273,7 @@ private:
     GrTextureStripAtlas* fAtlas;
     int fRow;
     SkMatrix fMatrix;
+    bool fIsOpaque;
 
     typedef GrEffect INHERITED;