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

src/core/SkBlitter_A8.cpp

Index: src/core/SkBlitter_A8.cpp
diff --git a/src/core/SkBlitter_A8.cpp b/src/core/SkBlitter_A8.cpp
index 983a226e3460a755bee4f80a287f3eb1b788eb41..04e8ccf134d503b991438b7676053a2ae157f6ef 100644
--- a/src/core/SkBlitter_A8.cpp
+++ b/src/core/SkBlitter_A8.cpp
@@ -228,11 +228,12 @@ void SkA8_Blitter::blitRect(int x, int y, int width, int height) {
 
 ///////////////////////////////////////////////////////////////////////
 
-SkA8_Shader_Blitter::SkA8_Shader_Blitter(const SkBitmap& device, const SkPaint& paint)
-    : INHERITED(device, paint) {
+SkA8_Shader_Blitter::SkA8_Shader_Blitter(const SkBitmap& device, const SkPaint& paint,
+                                         SkShader::Context* shaderContext)
+    : INHERITED(device, paint, shaderContext) {
     if ((fXfermode = paint.getXfermode()) != NULL) {
         fXfermode->ref();
-        SkASSERT(fShader);
+        SkASSERT(fShaderContext);
     }
 
     int width = device.width();
@@ -251,12 +252,12 @@ void SkA8_Shader_Blitter::blitH(int x, int y, int width) {
 
     uint8_t* device = fDevice.getAddr8(x, y);
 
-    if ((fShader->getFlags() & SkShader::kOpaqueAlpha_Flag) && !fXfermode) {
+    if ((fShaderContext->getFlags() & SkShader::kOpaqueAlpha_Flag) && !fXfermode) {
         memset(device, 0xFF, width);
     } else {
         SkPMColor*  span = fBuffer;
 
-        fShader->shadeSpan(x, y, span, width);
+        fShaderContext->shadeSpan(x, y, span, width);
         if (fXfermode) {
             fXfermode->xferA8(device, span, width, NULL);
         } else {
@@ -282,12 +283,12 @@ static inline uint8_t aa_blend8(SkPMColor src, U8CPU da, int aa) {
 
 void SkA8_Shader_Blitter::blitAntiH(int x, int y, const SkAlpha antialias[],
                                     const int16_t runs[]) {
-    SkShader*   shader = fShader;
+    SkShader::Context* shaderContext = fShaderContext;
     SkXfermode* mode = fXfermode;
     uint8_t*    aaExpand = fAAExpand;
     SkPMColor*  span = fBuffer;
     uint8_t*    device = fDevice.getAddr8(x, y);
-    int         opaque = fShader->getFlags() & SkShader::kOpaqueAlpha_Flag;
+    int         opaque = fShaderContext->getFlags() & SkShader::kOpaqueAlpha_Flag;

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

shaderContext?

 
     for (;;) {
         int count = *runs;
@@ -299,7 +300,7 @@ void SkA8_Shader_Blitter::blitAntiH(int x, int y, const SkAlpha antialias[],
             if (opaque && aa == 255 && mode == NULL) {
                 memset(device, 0xFF, count);
             } else {
-                shader->shadeSpan(x, y, span, count);
+                shaderContext->shadeSpan(x, y, span, count);
                 if (mode) {
                     memset(aaExpand, aa, count);
                     mode->xferA8(device, span, count, aaExpand);
@@ -333,7 +334,7 @@ void SkA8_Shader_Blitter::blitMask(const SkMask& mask, const SkIRect& clip) {
     SkPMColor*  span = fBuffer;
 
     while (--height >= 0) {
-        fShader->shadeSpan(x, y, span, width);
+        fShaderContext->shadeSpan(x, y, span, width);

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

I wonder why we chose not to cache fShader here. Would it make sense to cache
fShaderContext like we do in blitAntiH?

         if (fXfermode) {
             fXfermode->xferA8(device, span, width, alpha);
         } else {