restore lost optimization when the shader can report const_in_y

src/core/SkBitmapProcShader.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmapProcShader.h"
 #include "SkBitmapProcState.h"
 #include "SkBitmapProvider.h"
@@ skipping 81 matching lines @@
     }
 
     return new (storage) BitmapProcShaderContext(shader, rec, state);
 }
 
 SkShader::Context* SkBitmapProcShader::onCreateContext(const ContextRec& rec, void* storage) const {
     return MakeContext(*this, (TileMode)fTileModeX, (TileMode)fTileModeY,
                        SkBitmapProvider(fRawBitmap), rec, storage);
 }
 
+static bool only_scale_and_translate(const SkMatrix& matrix) {
+    unsigned mask = SkMatrix::kTranslate_Mask | SkMatrix::kScale_Mask;
+    return (matrix.getType() & ~mask) == 0;
+}
+
 SkBitmapProcShader::BitmapProcShaderContext::BitmapProcShaderContext(const SkShader& shader,
                                                                      const ContextRec& rec,
                                                                      SkBitmapProcState* state)
     : INHERITED(shader, rec)
     , fState(state)
 {
     fFlags = 0;
     if (fState->fPixmap.isOpaque() && (255 == this->getPaintAlpha())) {
         fFlags |= kOpaqueAlpha_Flag;
     }
+
+    if (1 == fState->fPixmap.height() && only_scale_and_translate(this->getTotalInverse())) {
+        fFlags |= kConstInY32_Flag;
+    }
 }
 
 SkBitmapProcShader::BitmapProcShaderContext::~BitmapProcShaderContext() {
     // The bitmap proc state has been created outside of the context on memory that will be freed
     // elsewhere. Only call the destructor but leave the freeing of the memory to the caller.
     fState->~SkBitmapProcState();
 }
 
 #define BUF_MAX     128
 
@@ skipping 212 matching lines @@
         inner.reset(GrSimpleTextureEffect::Create(texture, matrix, params));
     }
 
     if (kAlpha_8_SkColorType == fRawBitmap.colorType()) {
         return GrFragmentProcessor::MulOutputByInputUnpremulColor(inner);
     }
     return GrFragmentProcessor::MulOutputByInputAlpha(inner);
 }
 
 #endif