Extract most of the mutable state of SkShader into a separate Context object.

src/effects/SkTransparentShader.cpp

Index: src/effects/SkTransparentShader.cpp
diff --git a/src/effects/SkTransparentShader.cpp b/src/effects/SkTransparentShader.cpp
index 9de4a0cc23423d14ec451d7f5237b554341aad90..6a1a116b09e5af2e00e948cd1cf8fd36b6219bb9 100644
--- a/src/effects/SkTransparentShader.cpp
+++ b/src/effects/SkTransparentShader.cpp
@@ -11,16 +11,37 @@
 #include "SkColorPriv.h"
 #include "SkString.h"
 
-bool SkTransparentShader::setContext(const SkBitmap& device,
-                                     const SkPaint& paint,
-                                     const SkMatrix& matrix) {
-    fDevice = &device;
-    fAlpha = paint.getAlpha();
+SkShader::Context* SkTransparentShader::createContext(const SkBitmap& device,
+                                                      const SkPaint& paint,
+                                                      const SkMatrix& matrix,
+                                                      void* storage) const {
+    if (!this->validContext(device, paint, matrix)) {
+        return NULL;
+    }
+
+    return SkNEW_PLACEMENT_ARGS(storage, TransparentShaderContext, (*this, device, paint, matrix));
+}
 
-    return this->INHERITED::setContext(device, paint, matrix);
+size_t SkTransparentShader::contextSize() const {
+    return sizeof(TransparentShaderContext);
 }
 
-uint32_t SkTransparentShader::getFlags() {
+bool SkTransparentShader::validContext(const SkBitmap& device,

[scroggo, 2014/03/24 21:24:46]

Why did you override this if all you do is call inherited?

[Dominik Grewe, 2014/03/26 17:22:22]

Removed it.

+                                       const SkPaint& paint,
+                                       const SkMatrix& matrix) const {
+    return this->INHERITED::validContext(device, paint, matrix);
+}
+
+SkTransparentShader::TransparentShaderContext::TransparentShaderContext(
+    const SkTransparentShader& shader, const SkBitmap& device,

[scroggo, 2014/03/24 21:24:46]

nit: 8 space indent.

[Dominik Grewe, 2014/03/26 17:22:22]

Done.

+    const SkPaint& paint, const SkMatrix& matrix)
+    : INHERITED(shader, device, paint, matrix)
+    , fDevice(&device)
+    , fAlpha(paint.getAlpha()) {}

[scroggo, 2014/03/24 21:24:46]

fAlpha wasn't created by you, but as long as we're modifying this code - isn't
it redundant? Can't you call getPaintAlpha() when you need it?

[Dominik Grewe, 2014/03/26 17:22:22]

Done.

+
+SkTransparentShader::TransparentShaderContext::~TransparentShaderContext() {}
+
+uint32_t SkTransparentShader::TransparentShaderContext::getFlags() const {
     uint32_t flags = this->INHERITED::getFlags();
 
     switch (fDevice->colorType()) {
@@ -39,7 +60,8 @@ uint32_t SkTransparentShader::getFlags() {
     return flags;
 }
 
-void SkTransparentShader::shadeSpan(int x, int y, SkPMColor span[], int count) {
+void SkTransparentShader::TransparentShaderContext::shadeSpan(
+        int x, int y, SkPMColor span[], int count) {

[scroggo, 2014/03/24 21:24:46]

nit: The parameters that fit on the same line should remain on the initial line.

     unsigned scale = SkAlpha255To256(fAlpha);
 
     switch (fDevice->colorType()) {
@@ -97,7 +119,8 @@ void SkTransparentShader::shadeSpan(int x, int y, SkPMColor span[], int count) {
     }
 }
 
-void SkTransparentShader::shadeSpan16(int x, int y, uint16_t span[], int count) {
+void SkTransparentShader::TransparentShaderContext::shadeSpan16(
+        int x, int y, uint16_t span[], int count) {

[scroggo, 2014/03/24 21:24:46]

same.

     SkASSERT(fDevice->colorType() == kRGB_565_SkColorType);
 
     uint16_t* src = fDevice->getAddr16(x, y);