Implement support for mixed sampled render targets

src/gpu/GrStencilAndCoverTextContext.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 "GrStencilAndCoverTextContext.h"
 #include "GrBitmapTextContext.h"
 #include "GrDrawTarget.h"
@@ skipping 44 matching lines @@
         return false;
     }
 
     // No hairlines unless we can map the 1 px width to the object space.
     if (skPaint.getStyle() == SkPaint::kStroke_Style
         && skPaint.getStrokeWidth() == 0
         && viewMatrix.hasPerspective()) {
         return false;
     }
 
+    if (skPaint.isAntiAlias() &&
+        kStencil_GrSampleConfig == rt->sampleConfig() &&
+        !paint.getXPFactory()->canTweakAlphaForCoverage()) {

[Chris Dalton, 2015/03/26 05:11:39]

We may need to check if it will do in-shader blending as well. Maybe something
like this:

if (skPaint.isAntiAlias() &&
    kStencil_GrSampleConfig == rt->sampleConfig() &&
    (!paint.getXPFactory()->canTweakAlphaForCoverage() ||
     paint.getXPFactory()->willNeedDstCopy(this->getGpu()->caps(),
some_conservative_GrProcOptInfos...))) {

Is there an easy way to know if an xfer processor will potentially do in-shader
blending?

Since coverage gets modulated into the color *after* the fragment shader
(stencil test), in-shader blending won't work right now. (Though we could
theoretically support in-shader blending if we used ARB_blend_func_extended to
do an additional coverage modulation after the shader...)

[bsalomon, 2015/03/31 16:37:33]

I think your concern is correct. Adding egdaniel@ for commenting on how to know
if in shader blending will occur. Greg, do we always know at this point?

I think you're right that this could always work with ARB_blend_func_extended.
Set output0 = <fragment shader computed coverage> and output1 = <fragment shader
blended color>. output0 gets further modulated by COVERAGE_MODULATION. Set the
blend coeffs to GL_SRC1_COLOR SRC1 and GL_ONE_MINUS_SRC1_COLOR.

Moreover, we could force xp's that don't allow tweak-alpha-for-coverage into
doing frag shader blending in order to be able to always use
mixedsample/COVERAGE_MODULATION.

+        return false;
+    }
+
     // No color bitmap fonts.
     SkScalerContext::Rec    rec;
     SkScalerContext::MakeRec(skPaint, &fDeviceProperties, NULL, &rec);
     return rec.getFormat() != SkMask::kARGB32_Format;
 }
 
 void GrStencilAndCoverTextContext::onDrawText(GrRenderTarget* rt,
                                               const GrClip& clip,
                                               const GrPaint& paint,
                                               const SkPaint& skPaint,
@@ skipping 280 matching lines @@
         fGlyphCache = fSkPaint.detachCache(&fDeviceProperties, NULL, true /*ignoreGamma*/);
         fGlyphs = canUseRawPaths ?
                       get_gr_glyphs(fContext, fSkPaint.getTypeface(), NULL, fStroke) :
                       get_gr_glyphs(fContext, fGlyphCache->getScalerContext()->getTypeface(),
                                     &fGlyphCache->getDescriptor(), fStroke);
     }
 
     fStateRestore.set(&fPipelineBuilder);
 
     fPipelineBuilder.setFromPaint(fPaint, fRenderTarget, fClip);
+    SkASSERT(fRenderTarget->isMultisampled(GrRenderTarget::kStencilBuffer_PipelineStage));
+    fPipelineBuilder.setState(GrPipelineBuilder::kHWAntialias_StateBit, fPaint.isAntiAlias());
 
     GR_STATIC_CONST_SAME_STENCIL(kStencilPass,
                                  kZero_StencilOp,
                                  kZero_StencilOp,
                                  kNotEqual_StencilFunc,
                                  0xffff,
                                  0x0000,
                                  0xffff);
 
     *fPipelineBuilder.stencil() = kStencilPass;
@@ skipping 92 matching lines @@
 
     SkGlyphCache::AttachCache(fGlyphCache);
     fGlyphCache = NULL;
 
     fPipelineBuilder.stencil()->setDisabled();
     fStateRestore.set(NULL);
     fViewMatrix = fContextInitialMatrix;
     GrTextContext::finish();
 }