alpha threshold bitmap shader

src/gpu/SkGpuDevice.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 "SkGpuDevice.h"
 
 #include "effects/GrTextureDomainEffect.h"
@@ skipping 517 matching lines @@
 // same meaning as in skPaint2GrPaintNoShader.
 inline bool skPaint2GrPaintShader(SkGpuDevice* dev,
                                   const SkPaint& skPaint,
                                   bool constantColor,
                                   GrPaint* grPaint) {
     SkShader* shader = skPaint.getShader();
     if (NULL == shader) {
         return skPaint2GrPaintNoShader(dev, skPaint, false, constantColor, grPaint);
     }
 
+    // SkShader::asNewEffect() may do offscreen rendering. Setup default drawing state
+    // Also require shader to set the render target .
+    GrContext::AutoWideOpenIdentityDraw awo(dev->context(), NULL);
+    GrContext::AutoRenderTarget(dev->context(), NULL);
+
     // setup the shader as the first color effect on the paint
     SkAutoTUnref<GrEffectRef> effect(shader->asNewEffect(dev->context(), skPaint));
     if (NULL != effect.get()) {
         grPaint->addColorEffect(effect);
         // Now setup the rest of the paint.
         return skPaint2GrPaintNoShader(dev, skPaint, true, false, grPaint);
     } else {
         // We still don't have SkColorShader::asNewEffect() implemented.
         SkShader::GradientInfo info;
         SkColor                color;
@@ skipping 1311 matching lines @@
                          GrTexture* texture,
                          bool needClear)
     : SkBitmapDevice(make_bitmap(context, texture->asRenderTarget())) {
 
     SkASSERT(texture && texture->asRenderTarget());
     // This constructor is called from onCreateCompatibleDevice. It has locked the RT in the texture
     // cache. We pass true for the third argument so that it will get unlocked.
     this->initFromRenderTarget(context, texture->asRenderTarget(), true);
     fNeedClear = needClear;
 }