Simple GPU based dithering

src/gpu/SkGr.cpp

 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkGr.h"
 #include "SkColorFilter.h"
 #include "SkConfig8888.h"
 #include "SkData.h"
 #include "SkMessageBus.h"
 #include "SkPixelRef.h"
 #include "GrResourceCache.h"
 #include "GrGpu.h"
+#include "effects/GrDitherEffect.h"
 #include "GrDrawTargetCaps.h"
 
 #ifndef SK_IGNORE_ETC1_SUPPORT
 #  include "ktx.h"
 #  include "etc1.h"
 #endif
 
 /*  Fill out buffer with the compressed format Ganesh expects from a colortable
  based bitmap. [palette (colortable) + indices].
 
@@ skipping 432 matching lines @@
         if (constantColor) {
             SkColor filtered = colorFilter->filterColor(skPaint.getColor());
             grPaint->setColor(SkColor2GrColor(filtered));
         } else {
             SkAutoTUnref<GrEffectRef> effect(colorFilter->asNewEffect(context));
             if (NULL != effect.get()) {
                 grPaint->addColorEffect(effect);
             }
         }
     }
+

[robertphillips, 2014/06/11 17:20:24]

Wrap this in SK_IGNORE_GPU_DITHER and add it to
gyp/skia_for_chromium_defines.gypi? This will allow us to land this and roll it
into Chromium without having to worry about layout test regressions. Once it is
rolled we can rebaseline the Blink layout tests and remove the flag.

[krajcevski, 2014/06/11 22:33:18]

Done.

+    // If the dither flag is set, then we need to see if the underlying context
+    // supports it. If not, then install a dither effect.
+    if (skPaint.isDither()) {
+        // What are we rendering into?
+        const GrRenderTarget *target = context->getRenderTarget();
+        if (NULL == target) {
+            target = context->getGpu()->getDrawState().getRenderTarget();
+        }
+        SkASSERT(NULL != target);
+
+        if (target->config() == kRGBA_8888_GrPixelConfig ||
+            target->config() == kBGRA_8888_GrPixelConfig) {
+            // The dither flag is set and the target is likely
+            // not going to be dithered by the GPU.
+            SkAutoTUnref<GrEffectRef> effect(GrDitherEffect::Create());
+            if (NULL != effect.get()) {
+                grPaint->addColorEffect(effect);
+                grPaint->setDither(false);
+            }
+        }
+    }
 }
 
 /**
  * Unlike GrContext::AutoMatrix, this doesn't require setting a new matrix. GrContext::AutoMatrix
  * likes to set the new matrix in its constructor because it is usually necessary to simulataneously
  * update a GrPaint. This AutoMatrix is used while initially setting up GrPaint, however.
  */
 class AutoMatrix {
 public:
     AutoMatrix(GrContext* context) {
@@ skipping 43 matching lines @@
             copy.setShader(NULL);
             // modulate the paint alpha by the shader's solid color alpha
             U8CPU newA = SkMulDiv255Round(SkColorGetA(color), copy.getAlpha());
             copy.setColor(SkColorSetA(color, newA));
             SkPaint2GrPaintNoShader(context, copy, false, constantColor, grPaint);
         } else {
             SkPaint2GrPaintNoShader(context, skPaint, false, constantColor, grPaint);
         }
     }
 }