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

src/core/SkPictureShader.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkPictureShader.h"
 
 #include "SkBitmap.h"
@@ skipping 37 matching lines @@
     this->INHERITED::flatten(buffer);
 
     buffer.write32(fTmx);
     buffer.write32(fTmy);
     buffer.writeBool(NULL != fPicture);
     if (fPicture) {
         fPicture->flatten(buffer);
     }
 }
 
-bool SkPictureShader::buildBitmapShader(const SkMatrix& matrix) const {
+SkShader* SkPictureShader::buildBitmapShader(const SkMatrix& matrix) const {
     if (!fPicture || (0 == fPicture->width() && 0 == fPicture->height())) {
-        return false;
+        return NULL;
     }
 
     SkMatrix m;
     if (this->hasLocalMatrix()) {
         m.setConcat(matrix, this->getLocalMatrix());
     } else {
         m = matrix;
     }
 
     // Use a rotation-invariant scale
     SkPoint scale;
     if (!SkDecomposeUpper2x2(m, NULL, &scale, NULL)) {
         // Decomposition failed, use an approximation.
         scale.set(SkScalarSqrt(m.getScaleX() * m.getScaleX() + m.getSkewX() * m.getSkewX()),
                   SkScalarSqrt(m.getScaleY() * m.getScaleY() + m.getSkewY() * m.getSkewY()));
     }
     SkSize scaledSize = SkSize::Make(scale.x() * fPicture->width(), scale.y() * fPicture->height());
 
     SkISize tileSize = scaledSize.toRound();
     if (tileSize.isEmpty()) {
-        return false;
+        return NULL;
     }
 
     // The actual scale, compensating for rounding.
     SkSize tileScale = SkSize::Make(SkIntToScalar(tileSize.width()) / fPicture->width(),
                                     SkIntToScalar(tileSize.height()) / fPicture->height());
 
-    if (!fCachedShader || tileScale != fCachedTileScale) {
+    SkAutoMutexAcquire ama(fCachedBitmapShaderMutex);
+
+    if (!fCachedBitmapShader || tileScale != fCachedTileScale ||
+        this->getLocalMatrix() != fCachedLocalMatrix) {
         SkBitmap bm;
         if (!bm.allocN32Pixels(tileSize.width(), tileSize.height())) {
-            return false;
+            return NULL;
         }
         bm.eraseColor(SK_ColorTRANSPARENT);
 
         SkCanvas canvas(bm);
         canvas.scale(tileScale.width(), tileScale.height());
         canvas.drawPicture(*fPicture);
 
-        fCachedShader.reset(CreateBitmapShader(bm, fTmx, fTmy));
+        fCachedBitmapShader.reset(CreateBitmapShader(bm, fTmx, fTmy));
         fCachedTileScale = tileScale;
+        fCachedLocalMatrix = this->getLocalMatrix();
+
+        SkMatrix shaderMatrix = this->getLocalMatrix();
+        shaderMatrix.preScale(1 / tileScale.width(), 1 / tileScale.height());
+        fCachedBitmapShader->setLocalMatrix(shaderMatrix);
     }
 
-    SkMatrix shaderMatrix = this->getLocalMatrix();
-    shaderMatrix.preScale(1 / tileScale.width(), 1 / tileScale.height());
-    fCachedShader->setLocalMatrix(shaderMatrix);
-
-    return true;
+    // Increment the ref counter inside the mutex to ensure the returned pointer is still valid.
+    // Otherwise, the object pointed to may have already been overwritten on a different thread.
+    fCachedBitmapShader.get()->ref();
+    return fCachedBitmapShader;
 }
 
-bool SkPictureShader::setContext(const SkBitmap& device,
-                                 const SkPaint& paint,
-                                 const SkMatrix& matrix) {
-    if (!this->buildBitmapShader(matrix)) {
-        return false;
+SkShader* SkPictureShader::validInternal(const SkBitmap& device, const SkPaint& paint,
+                                         const SkMatrix& matrix, SkMatrix* totalInverse) const {
+    if (!this->INHERITED::validContext(device, paint, matrix, totalInverse)) {
+        return NULL;
     }
 
-    if (!this->INHERITED::setContext(device, paint, matrix)) {
-        return false;
+    SkShader* bitmapShader = this->buildBitmapShader(matrix);
+    if (!bitmapShader) {
+        return NULL;
     }
 
-    SkASSERT(fCachedShader);
-    if (!fCachedShader->setContext(device, paint, matrix)) {
-        this->INHERITED::endContext();
-        return false;
+    if (!bitmapShader->validContext(device, paint, matrix)) {
+        bitmapShader->unref();
+        return NULL;
     }
 
-    return true;
+    return bitmapShader;
 }
 
-void SkPictureShader::endContext() {
-    SkASSERT(fCachedShader);
-    fCachedShader->endContext();
-
-    this->INHERITED::endContext();
+bool SkPictureShader::validContext(const SkBitmap& device, const SkPaint& paint,
+                                   const SkMatrix& matrix, SkMatrix* totalInverse) const {
+    SkAutoTUnref<SkShader> shader(this->validInternal(device, paint, matrix, totalInverse));
+    return shader != NULL;
 }
 
-uint32_t SkPictureShader::getFlags() {
-    if (NULL != fCachedShader) {
-        return fCachedShader->getFlags();
+SkShader::Context* SkPictureShader::createContext(const SkBitmap& device, const SkPaint& paint,
+                                                  const SkMatrix& matrix, void* storage) const {
+    SkShader* bitmapShader = this->validInternal(device, paint, matrix, NULL);
+    if (!bitmapShader) {
+        return NULL;
     }
-    return 0;
+
+    return SkNEW_PLACEMENT_ARGS(storage, PictureShaderContext,
+                                (*this, device, paint, matrix, bitmapShader));
 }
 
-SkShader::ShadeProc SkPictureShader::asAShadeProc(void** ctx) {
-    if (fCachedShader) {
-        return fCachedShader->asAShadeProc(ctx);
-    }
-    return NULL;
+size_t SkPictureShader::contextSize() const {
+    return sizeof(PictureShaderContext);
 }
 
-void SkPictureShader::shadeSpan(int x, int y, SkPMColor dstC[], int count) {
-    SkASSERT(fCachedShader);
-    fCachedShader->shadeSpan(x, y, dstC, count);
+SkPictureShader::PictureShaderContext::PictureShaderContext(
+        const SkPictureShader& shader, const SkBitmap& device,
+        const SkPaint& paint, const SkMatrix& matrix, SkShader* bitmapShader)
+    : INHERITED(shader, device, paint, matrix)
+    , fBitmapShader(bitmapShader)
+{
+    SkASSERT(fBitmapShader);
+    fBitmapShaderContextStorage = sk_malloc_throw(fBitmapShader->contextSize());
+    fBitmapShaderContext = fBitmapShader->createContext(
+            device, paint, matrix, fBitmapShaderContextStorage);
+    SkASSERT(fBitmapShaderContext);
 }
 
-void SkPictureShader::shadeSpan16(int x, int y, uint16_t dstC[], int count) {
-    SkASSERT(fCachedShader);
-    fCachedShader->shadeSpan16(x, y, dstC, count);
+SkPictureShader::PictureShaderContext::~PictureShaderContext() {
+    fBitmapShaderContext->SkShader::Context::~Context();
+    sk_free(fBitmapShaderContextStorage);
+}
+
+uint32_t SkPictureShader::PictureShaderContext::getFlags() const {
+    return fBitmapShaderContext->getFlags();
+}
+
+SkShader::Context::ShadeProc SkPictureShader::PictureShaderContext::asAShadeProc(void** ctx) {
+    return fBitmapShaderContext->asAShadeProc(ctx);
+}
+
+void SkPictureShader::PictureShaderContext::shadeSpan(int x, int y, SkPMColor dstC[], int count) {
+    SkASSERT(fBitmapShaderContext);
+    fBitmapShaderContext->shadeSpan(x, y, dstC, count);
+}
+
+void SkPictureShader::PictureShaderContext::shadeSpan16(int x, int y, uint16_t dstC[], int count) {
+    SkASSERT(fBitmapShaderContext);
+    fBitmapShaderContext->shadeSpan16(x, y, dstC, count);
 }
 
 #ifndef SK_IGNORE_TO_STRING
 void SkPictureShader::toString(SkString* str) const {
     static const char* gTileModeName[SkShader::kTileModeCount] = {
         "clamp", "repeat", "mirror"
     };
 
     str->appendf("PictureShader: [%d:%d] ",
                  fPicture ? fPicture->width() : 0,
                  fPicture ? fPicture->height() : 0);
 
     str->appendf("(%s, %s)", gTileModeName[fTmx], gTileModeName[fTmy]);
 
     this->INHERITED::toString(str);
 }
 #endif
 
 #if SK_SUPPORT_GPU
 GrEffectRef* SkPictureShader::asNewEffect(GrContext* context, const SkPaint& paint) const {
-    if (!this->buildBitmapShader(context->getMatrix())) {
+    SkAutoTUnref<SkShader> bitmapShader(this->buildBitmapShader(context->getMatrix()));
+    if (!bitmapShader) {
         return NULL;
     }
-    SkASSERT(fCachedShader);
-    return fCachedShader->asNewEffect(context, paint);
+    return bitmapShader->asNewEffect(context, paint);
 }
 #endif