Implement support for mixed sampled render targets

src/gpu/GrStencilAndCoverTextContext.cpp

Index: src/gpu/GrStencilAndCoverTextContext.cpp
diff --git a/src/gpu/GrStencilAndCoverTextContext.cpp b/src/gpu/GrStencilAndCoverTextContext.cpp
index 9702ed706e5679ce9a45ff987f25dc9792f97537..330256ae390b6635b0721127c5c1ff8647204ca6 100644
--- a/src/gpu/GrStencilAndCoverTextContext.cpp
+++ b/src/gpu/GrStencilAndCoverTextContext.cpp
@@ -62,6 +62,12 @@ bool GrStencilAndCoverTextContext::canDraw(const GrRenderTarget* rt,
         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);
@@ -362,6 +368,8 @@ void GrStencilAndCoverTextContext::init(GrRenderTarget* rt,
     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,