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 427 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);
             }
         }
     }
+
+#ifndef SK_IGNORE_GPU_DITHER
+    // 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();
+        SkASSERT(NULL != target);
+
+        // Suspect the dithering flag has no effect on these configs, otherwise
+        // fall back on setting the appropriate state.
+        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);
+            }
+        }
+    }
+#endif
 }
 
 /**
  * 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 14 matching lines @@
     SkShader* shader = skPaint.getShader();
     if (NULL == shader) {
         SkPaint2GrPaintNoShader(context, skPaint, SkColor2GrColor(skPaint.getColor()),
                                 constantColor, grPaint);
         return;
     }
 
     // SkShader::asNewEffect() may do offscreen rendering. Save off the current RT, clip, and
     // matrix. We don't reset the matrix on the context because SkShader::asNewEffect may use
     // GrContext::getMatrix() to know the transformation from local coords to device space.
-    GrContext::AutoRenderTarget art(context, NULL);
-    GrContext::AutoClip ac(context, GrContext::AutoClip::kWideOpen_InitialClip);
-    AutoMatrix am(context);
+    GrColor grColor = SkColor2GrColor(skPaint.getColor());
+    {

[bsalomon, 2014/06/19 13:33:27]

Can you add a comment that this block is here to restore the context state after
asNewEffect is called. I'm just concerned that we'll forget why this was done
and remove what appear to be unnecessary braces.

[krajcevski, 2014/06/19 13:51:43]

Done.

+        GrContext::AutoRenderTarget art(context, NULL);
+        GrContext::AutoClip ac(context, GrContext::AutoClip::kWideOpen_InitialClip);
+        AutoMatrix am(context);
 
-    // setup the shader as the first color effect on the paint
-    // the default grColor is the paint's color
-    GrColor grColor = SkColor2GrColor(skPaint.getColor());
-    GrEffectRef* grEffect = NULL;
-    if (shader->asNewEffect(context, skPaint, NULL, &grColor, &grEffect) && NULL != grEffect) {
-        SkAutoTUnref<GrEffectRef> effect(grEffect);
-        grPaint->addColorEffect(effect);
-        constantColor = false;
+        // setup the shader as the first color effect on the paint
+        // the default grColor is the paint's color
+        GrEffectRef* grEffect = NULL;
+        if (shader->asNewEffect(context, skPaint, NULL, &grColor, &grEffect) && NULL != grEffect) {
+            SkAutoTUnref<GrEffectRef> effect(grEffect);
+            grPaint->addColorEffect(effect);
+            constantColor = false;
+        }
     }
+
     // The grcolor is automatically set when calling asneweffect.
     // If the shader can be seen as an effect it returns true and adds its effect to the grpaint.
     SkPaint2GrPaintNoShader(context, skPaint, grColor, constantColor, grPaint);
 }