Implement support for KHR_blend_equation_advanced

Uses KHR(or NV)_blend_equation_advanced to implement custom Xfer modes
in hardware.

BUG=skia:

Review URL: https://codereview.chromium.org/1037123003

3 files changed, 69 insertions, 2 deletions

diff --git a/src/gpu/gl/builders/GrGLFragmentShaderBuilder.cpp b/src/gpu/gl/builders/GrGLFragmentShaderBuilder.cpp
index 51a0340ea9..8fcb0b972e 100644
--- a/src/gpu/gl/builders/GrGLFragmentShaderBuilder.cpp
+++ b/src/gpu/gl/builders/GrGLFragmentShaderBuilder.cpp
@@ -36,6 +36,47 @@ static void append_default_precision_qualifier(GrSLPrecision p,
     }
 }
 
+static const char* specific_layout_qualifier_name(GrBlendEquation equation) {
+    SkASSERT(GrBlendEquationIsAdvanced(equation));
+
+    static const char* kLayoutQualifierNames[] = {
+        "blend_support_screen",
+        "blend_support_overlay",
+        "blend_support_darken",
+        "blend_support_lighten",
+        "blend_support_colordodge",
+        "blend_support_colorburn",
+        "blend_support_hardlight",
+        "blend_support_softlight",
+        "blend_support_difference",
+        "blend_support_exclusion",
+        "blend_support_multiply",
+        "blend_support_hsl_hue",
+        "blend_support_hsl_saturation",
+        "blend_support_hsl_color",
+        "blend_support_hsl_luminosity"
+    };
+    return kLayoutQualifierNames[equation - kFirstAdvancedGrBlendEquation];
+
+    GR_STATIC_ASSERT(0 == kScreen_GrBlendEquation - kFirstAdvancedGrBlendEquation);
+    GR_STATIC_ASSERT(1 == kOverlay_GrBlendEquation - kFirstAdvancedGrBlendEquation);
+    GR_STATIC_ASSERT(2 == kDarken_GrBlendEquation - kFirstAdvancedGrBlendEquation);
+    GR_STATIC_ASSERT(3 == kLighten_GrBlendEquation - kFirstAdvancedGrBlendEquation);
+    GR_STATIC_ASSERT(4 == kColorDodge_GrBlendEquation - kFirstAdvancedGrBlendEquation);
+    GR_STATIC_ASSERT(5 == kColorBurn_GrBlendEquation - kFirstAdvancedGrBlendEquation);
+    GR_STATIC_ASSERT(6 == kHardLight_GrBlendEquation - kFirstAdvancedGrBlendEquation);
+    GR_STATIC_ASSERT(7 == kSoftLight_GrBlendEquation - kFirstAdvancedGrBlendEquation);
+    GR_STATIC_ASSERT(8 == kDifference_GrBlendEquation - kFirstAdvancedGrBlendEquation);
+    GR_STATIC_ASSERT(9 == kExclusion_GrBlendEquation - kFirstAdvancedGrBlendEquation);
+    GR_STATIC_ASSERT(10 == kMultiply_GrBlendEquation - kFirstAdvancedGrBlendEquation);
+    GR_STATIC_ASSERT(11 == kHSLHue_GrBlendEquation - kFirstAdvancedGrBlendEquation);
+    GR_STATIC_ASSERT(12 == kHSLSaturation_GrBlendEquation - kFirstAdvancedGrBlendEquation);
+    GR_STATIC_ASSERT(13 == kHSLColor_GrBlendEquation - kFirstAdvancedGrBlendEquation);
+    GR_STATIC_ASSERT(14 == kHSLLuminosity_GrBlendEquation - kFirstAdvancedGrBlendEquation);
+    GR_STATIC_ASSERT(SK_ARRAY_COUNT(kLayoutQualifierNames) ==
+                     kTotalGrBlendEquationCount - kFirstAdvancedGrBlendEquation);
+}
+
 GrGLFragmentShaderBuilder::DstReadKey
 GrGLFragmentShaderBuilder::KeyForDstRead(const GrTexture* dstCopy, const GrGLCaps& caps) {
     uint32_t key = kYesDstRead_DstReadKeyBit;
@@ -183,6 +224,23 @@ const char* GrGLFragmentShaderBuilder::dstColor() {
     } 
 }
 
+void GrGLFragmentShaderBuilder::enableAdvancedBlendEquationIfNeeded(GrBlendEquation equation) {
+    SkASSERT(GrBlendEquationIsAdvanced(equation));
+
+    const GrGLSLCaps& caps = *fProgramBuilder->gpu()->glCaps().glslCaps();
+    if (!caps.mustEnableAdvBlendEqs()) {
+        return;
+    }
+
+    this->addFeature(1 << kBlendEquationAdvanced_GLSLPrivateFeature,
+                     "GL_KHR_blend_equation_advanced");
+    if (caps.mustEnableSpecificAdvBlendEqs()) {
+        this->addLayoutQualifier(specific_layout_qualifier_name(equation), kOut_InterfaceQualifier);
+    } else {
+        this->addLayoutQualifier("blend_support_all_equations", kOut_InterfaceQualifier);
+    }
+}
+
 void GrGLFragmentShaderBuilder::enableCustomOutput() {
     if (!fHasCustomColorOutput) {
         fHasCustomColorOutput = true;
diff --git a/src/gpu/gl/builders/GrGLFragmentShaderBuilder.h b/src/gpu/gl/builders/GrGLFragmentShaderBuilder.h
index 7afc76c711..1ab7af6b1b 100644
--- a/src/gpu/gl/builders/GrGLFragmentShaderBuilder.h
+++ b/src/gpu/gl/builders/GrGLFragmentShaderBuilder.h
@@ -66,6 +66,11 @@ public:
         no effect advertised that it will read the destination. */
     virtual const char* dstColor() = 0;
 
+    /** Adds any necessary layout qualifiers in order to legalize the supplied blend equation with
+        this shader. It is only legal to call this method with an advanced blend equation, and only
+        if these equations are supported. */
+    virtual void enableAdvancedBlendEquationIfNeeded(GrBlendEquation) = 0;
+
 private:
     typedef GrGLFragmentBuilder INHERITED;
 };
@@ -95,6 +100,8 @@ public:
     const char* fragmentPosition() override;
     const char* dstColor() override;
 
+    void enableAdvancedBlendEquationIfNeeded(GrBlendEquation) override;
+
 private:
     // Private public interface, used by GrGLProgramBuilder to build a fragment shader
     void enableCustomOutput();
@@ -123,7 +130,8 @@ private:
      */
     enum GLSLPrivateFeature {
         kFragCoordConventions_GLSLPrivateFeature = kLastGLSLFeature + 1,
-        kLastGLSLPrivateFeature = kFragCoordConventions_GLSLPrivateFeature
+        kBlendEquationAdvanced_GLSLPrivateFeature,
+        kLastGLSLPrivateFeature = kBlendEquationAdvanced_GLSLPrivateFeature
     };
 
     // Interpretation of DstReadKey when generating code
diff --git a/src/gpu/gl/builders/GrGLShaderBuilder.cpp b/src/gpu/gl/builders/GrGLShaderBuilder.cpp
index e885d36a43..67fbe2451d 100644
--- a/src/gpu/gl/builders/GrGLShaderBuilder.cpp
+++ b/src/gpu/gl/builders/GrGLShaderBuilder.cpp
@@ -173,7 +173,8 @@ void GrGLShaderBuilder::appendTextureLookup(const char* samplerName,
 }
 
 void GrGLShaderBuilder::addLayoutQualifier(const char* param, InterfaceQualifier interface) {
-    SkASSERT(fProgramBuilder->gpu()->glslGeneration() >= k330_GrGLSLGeneration);
+    SkASSERT(fProgramBuilder->gpu()->glslGeneration() >= k330_GrGLSLGeneration ||
+             fProgramBuilder->gpu()->glCaps().glslCaps()->mustEnableAdvBlendEqs());
     fLayoutParams[interface].push_back() = param;
 }