Adding isOpaque method to skia shader classes

REVIEW=http://codereview.appspot.com/5451102/
TEST=unit test ShaderOpacity



git-svn-id: http://skia.googlecode.com/svn/trunk@2840 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 21 insertions, 14 deletions

diff --git a/src/effects/SkGradientShader.cpp b/src/effects/SkGradientShader.cpp
index bc7f8a3a68..af357a624b 100644
--- a/src/effects/SkGradientShader.cpp
+++ b/src/effects/SkGradientShader.cpp
@@ -119,6 +119,7 @@ public:
     // overrides
     virtual bool setContext(const SkBitmap&, const SkPaint&, const SkMatrix&) SK_OVERRIDE;
     virtual uint32_t getFlags() SK_OVERRIDE { return fFlags; }
+    virtual bool isOpaque() const SK_OVERRIDE;
 
 protected:
     Gradient_Shader(SkFlattenableReadBuffer& );
@@ -161,7 +162,8 @@ private:
         kStorageSize = kColorStorageCount * (sizeof(SkColor) + sizeof(Rec))
     };
     SkColor     fStorage[(kStorageSize + 3) >> 2];
-    SkColor*    fOrigColors;
+    SkColor*    fOrigColors; // original colors, before modulation by paint in setContext
+    bool        fColorsAreOpaque;
 
     mutable uint16_t*   fCache16;   // working ptr. If this is NULL, we need to recompute the cache values
     mutable SkPMColor*  fCache32;   // working ptr. If this is NULL, we need to recompute the cache values
@@ -174,6 +176,7 @@ private:
     static void Build32bitCache(SkPMColor[], SkColor c0, SkColor c1, int count,
                                 U8CPU alpha);
     void setCacheAlpha(U8CPU alpha) const;
+    void initCommon();
 
     typedef SkShader INHERITED;
 };
@@ -302,7 +305,7 @@ Gradient_Shader::Gradient_Shader(const SkColor colors[], const SkScalar pos[],
             }
         }
     }
-    fFlags = 0;
+    this->initCommon();
 }
 
 Gradient_Shader::Gradient_Shader(SkFlattenableReadBuffer& buffer) :
@@ -336,7 +339,7 @@ Gradient_Shader::Gradient_Shader(SkFlattenableReadBuffer& buffer) :
         }
     }
     SkReadMatrix(&buffer, &fPtsToUnit);
-    fFlags = 0;
+    this->initCommon();
 }
 
 Gradient_Shader::~Gradient_Shader() {
@@ -350,6 +353,15 @@ Gradient_Shader::~Gradient_Shader() {
     SkSafeUnref(fMapper);
 }
 
+void Gradient_Shader::initCommon() {
+    fFlags = 0;
+    unsigned colorAlpha = 0xFF;
+    for (int i = 0; i < fColorCount; i++) {
+        colorAlpha &= SkColorGetA(fOrigColors[i]);
+    }
+    fColorsAreOpaque = colorAlpha == 0xFF;
+}
+
 void Gradient_Shader::flatten(SkFlattenableWriteBuffer& buffer) {
     this->INHERITED::flatten(buffer);
     buffer.writeFlattenable(fMapper);
@@ -366,6 +378,10 @@ void Gradient_Shader::flatten(SkFlattenableWriteBuffer& buffer) {
     SkWriteMatrix(&buffer, fPtsToUnit);
 }
 
+bool Gradient_Shader::isOpaque() const {
+    return fColorsAreOpaque;
+}
+
 bool Gradient_Shader::setContext(const SkBitmap& device,
                                  const SkPaint& paint,
                                  const SkMatrix& matrix) {
@@ -384,23 +400,14 @@ bool Gradient_Shader::setContext(const SkBitmap& device,
 
     // now convert our colors in to PMColors
     unsigned paintAlpha = this->getPaintAlpha();
-    unsigned colorAlpha = 0xFF;
-
-    // FIXME: record colorAlpha in constructor, since this is not affected
-    // by setContext()
-    for (int i = 0; i < fColorCount; i++) {
-        SkColor src = fOrigColors[i];
-        unsigned sa = SkColorGetA(src);
-        colorAlpha &= sa;
-    }
 
     fFlags = this->INHERITED::getFlags();
-    if ((colorAlpha & paintAlpha) == 0xFF) {
+    if (fColorsAreOpaque && paintAlpha == 0xFF) {
         fFlags |= kOpaqueAlpha_Flag;
     }
     // we can do span16 as long as our individual colors are opaque,
     // regardless of the paint's alpha
-    if (0xFF == colorAlpha) {
+    if (fColorsAreOpaque) {
         fFlags |= kHasSpan16_Flag;
     }