Add query to GrXPFactory about coverage-as-alpha optimization

This will be needed to have GrDrawOps that haven't yet built pipelines.

Change-Id: If5292aaa5dc9f98dccbe27be98960b630332158d
Reviewed-on: https://skia-review.googlesource.com/9480
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>

src/gpu/GrXferProcessor.cpp

@@ -197,6 +197,13 @@ bool GrXPFactory::WillNeedDstTexture(const GrXPFactory* factory, const GrCaps& c
     return result;
 }
 
+bool GrXPFactory::CompatibleWithCoverageAsAlpha(const GrXPFactory* factory, bool colorIsOpaque) {
+    if (factory) {
+        return factory->compatibleWithCoverageAsAlpha(colorIsOpaque);
+    }
+    return GrPorterDuffXPFactory::SrcOverIsCompatibleWithCoverageAsAlpha();
+}
+
 GrXferProcessor* GrXPFactory::createXferProcessor(const FragmentProcessorAnalysis& analysis,
                                                   bool hasMixedSamples,
                                                   const DstTexture* dstTexture,

src/gpu/GrXferProcessor.h

@@ -313,6 +313,8 @@ public:
                                    const GrCaps&,
                                    const FragmentProcessorAnalysis&);
 
+    static bool CompatibleWithCoverageAsAlpha(const GrXPFactory*, bool colorIsOpaque);
+
 protected:
     constexpr GrXPFactory() {}
 
@@ -330,6 +332,8 @@ private:
      *  shader.
      */
     virtual bool willReadDstInShader(const GrCaps&, const FragmentProcessorAnalysis&) const = 0;
+
+    virtual bool compatibleWithCoverageAsAlpha(bool colorIsOpaque) const = 0;
 };
 #if defined(__GNUC__) || defined(__clang)
 #pragma GCC diagnostic pop

src/gpu/effects/GrCoverageSetOpXP.h

@@ -45,6 +45,8 @@ private:
         return false;
     }
 
+    bool compatibleWithCoverageAsAlpha(bool colorIsOpaque) const override { return false; }
+
     GR_DECLARE_XP_FACTORY_TEST;
 
     SkRegion::Op fRegionOp;

src/gpu/effects/GrCustomXfermode.cpp

@@ -331,6 +331,8 @@ private:
 
     bool willReadDstInShader(const GrCaps&, const FragmentProcessorAnalysis&) const override;
 
+    bool compatibleWithCoverageAsAlpha(bool colorIsOpaque) const override { return true; }
+
     GR_DECLARE_XP_FACTORY_TEST;
 
     SkBlendMode     fMode;

src/gpu/effects/GrDisableColorXP.h

@@ -32,6 +32,8 @@ private:
         return false;
     }
 
+    bool compatibleWithCoverageAsAlpha(bool colorIsOpaque) const override { return true; }
+
     GrXferProcessor* onCreateXferProcessor(const GrCaps& caps,
                                            const FragmentProcessorAnalysis&,
                                            bool hasMixedSamples,

src/gpu/effects/GrPorterDuffXferProcessor.cpp

@@ -791,6 +791,11 @@ bool GrPorterDuffXPFactory::willReadDstInShader(const GrCaps& caps,
     return formula.hasSecondaryOutput();
 }
 
+bool GrPorterDuffXPFactory::compatibleWithCoverageAsAlpha(bool colorIsOpaque) const {
+    // We assume we have coverage (or else this doesn't matter).
+    return gBlendTable[colorIsOpaque][1][(int)fBlendMode].canTweakAlphaForCoverage();
+}
+
 GR_DEFINE_XP_FACTORY_TEST(GrPorterDuffXPFactory);
 
 #if GR_TEST_UTILS
@@ -868,14 +873,6 @@ bool GrPorterDuffXPFactory::WillSrcOverReadDst(const FragmentProcessorAnalysis&
     return analysis.hasCoverage() || !analysis.isOutputColorOpaque();
 }
 
-bool GrPorterDuffXPFactory::IsSrcOverPreCoverageBlendedColorConstant(
-        const GrProcOptInfo& colorInput, GrColor* color) {
-    if (!colorInput.isOpaque()) {
-        return false;
-    }
-    return colorInput.hasKnownOutputColor(color);
-}
-
 bool GrPorterDuffXPFactory::WillSrcOverNeedDstTexture(const GrCaps& caps,
                                                       const FragmentProcessorAnalysis& analysis) {
     if (caps.shaderCaps()->dstReadInShaderSupport() ||

src/gpu/effects/GrPorterDuffXferProcessor.h

@@ -38,9 +38,8 @@ public:
     static const GrXferProcessor& SimpleSrcOverXP();
 
     static bool WillSrcOverReadDst(const FragmentProcessorAnalysis& analysis);
-    static bool IsSrcOverPreCoverageBlendedColorConstant(const GrProcOptInfo& colorInput,
-                                                         GrColor* color);
     static bool WillSrcOverNeedDstTexture(const GrCaps&, const FragmentProcessorAnalysis&);
+    static bool SrcOverIsCompatibleWithCoverageAsAlpha() { return true; }
 
 private:
     constexpr GrPorterDuffXPFactory(SkBlendMode);
@@ -54,6 +53,8 @@ private:
 
     bool willReadDstInShader(const GrCaps&, const FragmentProcessorAnalysis&) const override;
 
+    bool compatibleWithCoverageAsAlpha(bool colorIsOpaque) const override;
+
     GR_DECLARE_XP_FACTORY_TEST;
     static void TestGetXPOutputTypes(const GrXferProcessor*, int* outPrimary, int* outSecondary);