Move blend enums into GrBlend.h

Moves blend enums from GrXferProcessor.h to GrBlend.h, makes GrBlend.h
public.

BUG=skia:

Review URL: https://codereview.chromium.org/1180713008

2 files changed, 217 insertions, 60 deletions

diff --git a/include/gpu/GrBlend.h b/include/gpu/GrBlend.h
new file mode 100644
index 0000000000..c8b931da73
--- /dev/null
+++ b/include/gpu/GrBlend.h
@@ -0,0 +1,216 @@
+
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "GrTypes.h"
+#include "../../src/utils/SkTLogic.h"
+
+#ifndef GrBlend_DEFINED
+#define GrBlend_DEFINED
+
+/**
+ * Equations for alpha-blending.
+ */
+enum GrBlendEquation {
+    // Basic blend equations.
+    kAdd_GrBlendEquation,             //<! Cs*S + Cd*D
+    kSubtract_GrBlendEquation,        //<! Cs*S - Cd*D
+    kReverseSubtract_GrBlendEquation, //<! Cd*D - Cs*S
+
+    // Advanced blend equations. These are described in the SVG and PDF specs.
+    kScreen_GrBlendEquation,
+    kOverlay_GrBlendEquation,
+    kDarken_GrBlendEquation,
+    kLighten_GrBlendEquation,
+    kColorDodge_GrBlendEquation,
+    kColorBurn_GrBlendEquation,
+    kHardLight_GrBlendEquation,
+    kSoftLight_GrBlendEquation,
+    kDifference_GrBlendEquation,
+    kExclusion_GrBlendEquation,
+    kMultiply_GrBlendEquation,
+    kHSLHue_GrBlendEquation,
+    kHSLSaturation_GrBlendEquation,
+    kHSLColor_GrBlendEquation,
+    kHSLLuminosity_GrBlendEquation,
+
+    kFirstAdvancedGrBlendEquation = kScreen_GrBlendEquation,
+    kLast_GrBlendEquation = kHSLLuminosity_GrBlendEquation
+};
+
+static const int kGrBlendEquationCnt = kLast_GrBlendEquation + 1;
+
+
+/**
+ * Coeffecients for alpha-blending.
+ */
+enum GrBlendCoeff {
+    kZero_GrBlendCoeff,    //<! 0
+    kOne_GrBlendCoeff,     //<! 1
+    kSC_GrBlendCoeff,      //<! src color
+    kISC_GrBlendCoeff,     //<! one minus src color
+    kDC_GrBlendCoeff,      //<! dst color
+    kIDC_GrBlendCoeff,     //<! one minus dst color
+    kSA_GrBlendCoeff,      //<! src alpha
+    kISA_GrBlendCoeff,     //<! one minus src alpha
+    kDA_GrBlendCoeff,      //<! dst alpha
+    kIDA_GrBlendCoeff,     //<! one minus dst alpha
+    kConstC_GrBlendCoeff,  //<! constant color
+    kIConstC_GrBlendCoeff, //<! one minus constant color
+    kConstA_GrBlendCoeff,  //<! constant color alpha
+    kIConstA_GrBlendCoeff, //<! one minus constant color alpha
+    kS2C_GrBlendCoeff,
+    kIS2C_GrBlendCoeff,
+    kS2A_GrBlendCoeff,
+    kIS2A_GrBlendCoeff,
+
+    kLast_GrBlendCoeff = kIS2A_GrBlendCoeff
+};
+
+static const int kGrBlendCoeffCnt = kLast_GrBlendCoeff + 1;
+
+
+template<GrBlendCoeff Coeff>
+struct GrTBlendCoeffRefsSrc : SkTBool<kSC_GrBlendCoeff == Coeff ||
+                                      kISC_GrBlendCoeff == Coeff ||
+                                      kSA_GrBlendCoeff == Coeff ||
+                                      kISA_GrBlendCoeff == Coeff> {};
+
+#define GR_BLEND_COEFF_REFS_SRC(COEFF) \
+    GrTBlendCoeffRefsSrc<COEFF>::value
+
+inline bool GrBlendCoeffRefsSrc(GrBlendCoeff coeff) {
+    switch (coeff) {
+        case kSC_GrBlendCoeff:
+        case kISC_GrBlendCoeff:
+        case kSA_GrBlendCoeff:
+        case kISA_GrBlendCoeff:
+            return true;
+        default:
+            return false;
+    }
+}
+
+
+template<GrBlendCoeff Coeff>
+struct GrTBlendCoeffRefsDst : SkTBool<kDC_GrBlendCoeff == Coeff ||
+                                      kIDC_GrBlendCoeff == Coeff ||
+                                      kDA_GrBlendCoeff == Coeff ||
+                                      kIDA_GrBlendCoeff == Coeff> {};
+
+#define GR_BLEND_COEFF_REFS_DST(COEFF) \
+    GrTBlendCoeffRefsDst<COEFF>::value
+
+inline bool GrBlendCoeffRefsDst(GrBlendCoeff coeff) {
+    switch (coeff) {
+        case kDC_GrBlendCoeff:
+        case kIDC_GrBlendCoeff:
+        case kDA_GrBlendCoeff:
+        case kIDA_GrBlendCoeff:
+            return true;
+        default:
+            return false;
+    }
+}
+
+
+template<GrBlendCoeff Coeff>
+struct GrTBlendCoeffRefsSrc2 : SkTBool<kS2C_GrBlendCoeff == Coeff ||
+                                       kIS2C_GrBlendCoeff == Coeff ||
+                                       kS2A_GrBlendCoeff == Coeff ||
+                                       kIS2A_GrBlendCoeff == Coeff> {};
+
+#define GR_BLEND_COEFF_REFS_SRC2(COEFF) \
+    GrTBlendCoeffRefsSrc2<COEFF>::value
+
+inline bool GrBlendCoeffRefsSrc2(GrBlendCoeff coeff) {
+    switch (coeff) {
+        case kS2C_GrBlendCoeff:
+        case kIS2C_GrBlendCoeff:
+        case kS2A_GrBlendCoeff:
+        case kIS2A_GrBlendCoeff:
+            return true;
+        default:
+            return false;
+    }
+}
+
+
+template<GrBlendCoeff SrcCoeff, GrBlendCoeff DstCoeff>
+struct GrTBlendCoeffsUseSrcColor : SkTBool<kZero_GrBlendCoeff != SrcCoeff ||
+                                           GR_BLEND_COEFF_REFS_SRC(DstCoeff)> {};
+
+#define GR_BLEND_COEFFS_USE_SRC_COLOR(SRC_COEFF, DST_COEFF) \
+    GrTBlendCoeffsUseSrcColor<SRC_COEFF, DST_COEFF>::value
+
+
+template<GrBlendCoeff SrcCoeff, GrBlendCoeff DstCoeff>
+struct GrTBlendCoeffsUseDstColor : SkTBool<GR_BLEND_COEFF_REFS_DST(SrcCoeff) ||
+                                           kZero_GrBlendCoeff != DstCoeff> {};
+
+#define GR_BLEND_COEFFS_USE_DST_COLOR(SRC_COEFF, DST_COEFF) \
+    GrTBlendCoeffsUseDstColor<SRC_COEFF, DST_COEFF>::value
+
+
+template<GrBlendEquation Equation>
+struct GrTBlendEquationIsAdvanced : SkTBool<Equation >= kFirstAdvancedGrBlendEquation> {};
+
+#define GR_BLEND_EQUATION_IS_ADVANCED(EQUATION) \
+    GrTBlendEquationIsAdvanced<EQUATION>::value
+
+inline bool GrBlendEquationIsAdvanced(GrBlendEquation equation) {
+    return equation >= kFirstAdvancedGrBlendEquation;
+}
+
+
+template<GrBlendEquation BlendEquation, GrBlendCoeff SrcCoeff, GrBlendCoeff DstCoeff>
+struct GrTBlendModifiesDst : SkTBool<(kAdd_GrBlendEquation != BlendEquation &&
+                                      kReverseSubtract_GrBlendEquation != BlendEquation) ||
+                                     kZero_GrBlendCoeff != SrcCoeff ||
+                                     kOne_GrBlendCoeff != DstCoeff> {};
+
+#define GR_BLEND_MODIFIES_DST(EQUATION, SRC_COEFF, DST_COEFF) \
+    GrTBlendModifiesDst<EQUATION, SRC_COEFF, DST_COEFF>::value
+
+
+/**
+ * Advanced blend equations can always tweak alpha for coverage. (See GrCustomXfermode.cpp)
+ *
+ * For "add" and "reverse subtract" the blend equation with f=coverage is:
+ *
+ *   D' = f * (S * srcCoeff + D * dstCoeff) + (1-f) * D
+ *      = f * S * srcCoeff + D * (f * dstCoeff + (1 - f))
+ *
+ * (Let srcCoeff be negative for reverse subtract.) We can tweak alpha for coverage when the
+ * following relationship holds:
+ *
+ *   (f*S) * srcCoeff' + D * dstCoeff' == f * S * srcCoeff + D * (f * dstCoeff + (1 - f))
+ *
+ * (Where srcCoeff' and dstCoeff' have any reference to S pre-multiplied by f.)
+ *
+ * It's easy to see this works for the src term as long as srcCoeff' == srcCoeff (meaning srcCoeff
+ * does not reference S). For the dst term, this will work as long as the following is true:
+ *|
+ *   dstCoeff' == f * dstCoeff + (1 - f)
+ *   dstCoeff' == 1 - f * (1 - dstCoeff)
+ *
+ * By inspection we can see this will work as long as dstCoeff has a 1, and any other term in
+ * dstCoeff references S.
+ */
+template<GrBlendEquation Equation, GrBlendCoeff SrcCoeff, GrBlendCoeff DstCoeff>
+struct GrTBlendCanTweakAlphaForCoverage : SkTBool<GR_BLEND_EQUATION_IS_ADVANCED(Equation) ||
+                                                  ((kAdd_GrBlendEquation == Equation ||
+                                                    kReverseSubtract_GrBlendEquation == Equation) &&
+                                                   !GR_BLEND_COEFF_REFS_SRC(SrcCoeff) &&
+                                                   (kOne_GrBlendCoeff == DstCoeff ||
+                                                    kISC_GrBlendCoeff == DstCoeff ||
+                                                    kISA_GrBlendCoeff == DstCoeff))> {};
+
+#define GR_BLEND_CAN_TWEAK_ALPHA_FOR_COVERAGE(EQUATION, SRC_COEFF, DST_COEFF) \
+    GrTBlendCanTweakAlphaForCoverage<EQUATION, SRC_COEFF, DST_COEFF>::value
+
+#endif
diff --git a/include/gpu/GrXferProcessor.h b/include/gpu/GrXferProcessor.h
index 8f2c69d995..332d9d2e23 100644
--- a/include/gpu/GrXferProcessor.h
+++ b/include/gpu/GrXferProcessor.h
@@ -8,6 +8,7 @@
 #ifndef GrXferProcessor_DEFINED
 #define GrXferProcessor_DEFINED
 
+#include "GrBlend.h"
 #include "GrColor.h"
 #include "GrProcessor.h"
 #include "GrTexture.h"
@@ -20,66 +21,6 @@ class GrGLXferProcessor;
 class GrProcOptInfo;
 
 /**
- * Equations for alpha-blending.
- */
-enum GrBlendEquation {
-    // Basic blend equations.
-    kAdd_GrBlendEquation,             //<! Cs*S + Cd*D
-    kSubtract_GrBlendEquation,        //<! Cs*S - Cd*D
-    kReverseSubtract_GrBlendEquation, //<! Cd*D - Cs*S
-
-    // Advanced blend equations. These are described in the SVG and PDF specs.
-    kScreen_GrBlendEquation,
-    kOverlay_GrBlendEquation,
-    kDarken_GrBlendEquation,
-    kLighten_GrBlendEquation,
-    kColorDodge_GrBlendEquation,
-    kColorBurn_GrBlendEquation,
-    kHardLight_GrBlendEquation,
-    kSoftLight_GrBlendEquation,
-    kDifference_GrBlendEquation,
-    kExclusion_GrBlendEquation,
-    kMultiply_GrBlendEquation,
-    kHSLHue_GrBlendEquation,
-    kHSLSaturation_GrBlendEquation,
-    kHSLColor_GrBlendEquation,
-    kHSLLuminosity_GrBlendEquation,
-
-    kFirstAdvancedGrBlendEquation = kScreen_GrBlendEquation,
-    kLast_GrBlendEquation = kHSLLuminosity_GrBlendEquation
-};
-
-static const int kGrBlendEquationCnt = kLast_GrBlendEquation + 1;
-
-/**
- * Coeffecients for alpha-blending.
- */
-enum GrBlendCoeff {
-    kZero_GrBlendCoeff,    //<! 0
-    kOne_GrBlendCoeff,     //<! 1
-    kSC_GrBlendCoeff,      //<! src color
-    kISC_GrBlendCoeff,     //<! one minus src color
-    kDC_GrBlendCoeff,      //<! dst color
-    kIDC_GrBlendCoeff,     //<! one minus dst color
-    kSA_GrBlendCoeff,      //<! src alpha
-    kISA_GrBlendCoeff,     //<! one minus src alpha
-    kDA_GrBlendCoeff,      //<! dst alpha
-    kIDA_GrBlendCoeff,     //<! one minus dst alpha
-    kConstC_GrBlendCoeff,  //<! constant color
-    kIConstC_GrBlendCoeff, //<! one minus constant color
-    kConstA_GrBlendCoeff,  //<! constant color alpha
-    kIConstA_GrBlendCoeff, //<! one minus constant color alpha
-    kS2C_GrBlendCoeff,
-    kIS2C_GrBlendCoeff,
-    kS2A_GrBlendCoeff,
-    kIS2A_GrBlendCoeff,
-
-    kLast_GrBlendCoeff = kIS2A_GrBlendCoeff
-};
-
-static const int kGrBlendCoeffCnt = kLast_GrBlendCoeff + 1;
-
-/**
  * Barriers for blending. When a shader reads the dst directly, an Xfer barrier is sometimes
  * required after a pixel has been written, before it can be safely read again.
  */