Merge GrGLSLCaps into GrShaderCaps

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=5121

Change-Id: If8d13638f80f42161cbc766a2666c5789e5772c8
Reviewed-on: https://skia-review.googlesource.com/5121
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>

3 files changed, 664 insertions, 0 deletions

diff --git a/include/private/GrGLSL.h b/include/private/GrGLSL.h
new file mode 100644
index 0000000000..6d9e403cfe
--- /dev/null
+++ b/include/private/GrGLSL.h
@@ -0,0 +1,374 @@
+/*
+ * Copyright 2011 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrGLSL_DEFINED
+#define GrGLSL_DEFINED
+
+#include "GrTypesPriv.h"
+#include "SkString.h"
+
+class GrShaderCaps;
+
+// Limited set of GLSL versions we build shaders for. Caller should round
+// down the GLSL version to one of these enums.
+enum GrGLSLGeneration {
+    /**
+     * Desktop GLSL 1.10 and ES2 shading language (based on desktop GLSL 1.20)
+     */
+    k110_GrGLSLGeneration,
+    /**
+     * Desktop GLSL 1.30
+     */
+    k130_GrGLSLGeneration,
+    /**
+     * Desktop GLSL 1.40
+     */
+    k140_GrGLSLGeneration,
+    /**
+     * Desktop GLSL 1.50
+     */
+    k150_GrGLSLGeneration,
+    /**
+     * Desktop GLSL 3.30, and ES GLSL 3.00
+     */
+    k330_GrGLSLGeneration,
+    /**
+     * Desktop GLSL 4.00
+     */
+    k400_GrGLSLGeneration,
+    /**
+     * Desktop GLSL 4.20
+     */
+    k420_GrGLSLGeneration,
+    /**
+     * ES GLSL 3.10 only TODO Make GLSLCap objects to make this more granular
+     */
+    k310es_GrGLSLGeneration,
+    /**
+     * ES GLSL 3.20
+     */
+    k320es_GrGLSLGeneration,
+};
+
+bool GrGLSLSupportsNamedFragmentShaderOutputs(GrGLSLGeneration);
+
+/**
+ * Adds a line of GLSL code to declare the default precision for float types.
+ */
+void GrGLSLAppendDefaultFloatPrecisionDeclaration(GrSLPrecision,
+                                                  const GrShaderCaps&,
+                                                  SkString* out);
+
+/**
+ * Converts a GrSLPrecision to its corresponding GLSL precision qualifier.
+ */
+static inline const char* GrGLSLPrecisionString(GrSLPrecision p) {
+    switch (p) {
+        case kLow_GrSLPrecision:
+            return "lowp";
+        case kMedium_GrSLPrecision:
+            return "mediump";
+        case kHigh_GrSLPrecision:
+            return "highp";
+        default:
+            SkFAIL("Unexpected precision type.");
+            return "";
+    }
+}
+
+/**
+ * Converts a GrSLType to a string containing the name of the equivalent GLSL type.
+ */
+static inline const char* GrGLSLTypeString(GrSLType t) {
+    switch (t) {
+        case kVoid_GrSLType:
+            return "void";
+        case kFloat_GrSLType:
+            return "float";
+        case kVec2f_GrSLType:
+            return "vec2";
+        case kVec3f_GrSLType:
+            return "vec3";
+        case kVec4f_GrSLType:
+            return "vec4";
+        case kMat22f_GrSLType:
+            return "mat2";
+        case kMat33f_GrSLType:
+            return "mat3";
+        case kMat44f_GrSLType:
+            return "mat4";
+        case kTexture2DSampler_GrSLType:
+            return "sampler2D";
+        case kITexture2DSampler_GrSLType:
+            return "isampler2D";
+        case kTextureExternalSampler_GrSLType:
+            return "samplerExternalOES";
+        case kTexture2DRectSampler_GrSLType:
+            return "sampler2DRect";
+        case kBufferSampler_GrSLType:
+            return "samplerBuffer";
+        case kBool_GrSLType:
+            return "bool";
+        case kInt_GrSLType:
+            return "int";
+        case kUint_GrSLType:
+            return "uint";
+        case kTexture2D_GrSLType:
+            return "texture2D";
+        case kSampler_GrSLType:
+            return "sampler";
+        case kImageStorage2D_GrSLType:
+            return "image2D";
+        case kIImageStorage2D_GrSLType:
+            return "iimage2D";
+    }
+    SkFAIL("Unknown shader var type.");
+    return ""; // suppress warning
+}
+
+/** A generic base-class representing a GLSL expression.
+ * The instance can be a variable name, expression or vecN(0) or vecN(1). Does simple constant
+ * folding with help of 1 and 0.
+ *
+ * Clients should not use this class, rather the specific instantiations defined
+ * later, for example GrGLSLExpr4.
+ */
+template <typename Self>
+class GrGLSLExpr {
+public:
+    bool isOnes() const { return kOnes_ExprType == fType; }
+    bool isZeros() const { return kZeros_ExprType == fType; }
+
+    const char* c_str() const {
+        if (kZeros_ExprType == fType) {
+            return Self::ZerosStr();
+        } else if (kOnes_ExprType == fType) {
+            return Self::OnesStr();
+        }
+        SkASSERT(!fExpr.isEmpty()); // Empty expressions should not be used.
+        return fExpr.c_str();
+    }
+
+    bool isValid() const {
+        return kFullExpr_ExprType != fType || !fExpr.isEmpty();
+    }
+
+protected:
+    /** Constructs an invalid expression.
+     * Useful only as a return value from functions that never actually return
+     * this and instances that will be assigned to later. */
+    GrGLSLExpr()
+        : fType(kFullExpr_ExprType) {
+        // The only constructor that is allowed to build an empty expression.
+        SkASSERT(!this->isValid());
+    }
+
+    /** Constructs an expression with all components as value v */
+    explicit GrGLSLExpr(int v) {
+        if (v == 0) {
+            fType = kZeros_ExprType;
+        } else if (v == 1) {
+            fType = kOnes_ExprType;
+        } else {
+            fType = kFullExpr_ExprType;
+            fExpr.appendf(Self::CastIntStr(), v);
+        }
+    }
+
+    /** Constructs an expression from a string.
+     * Argument expr is a simple expression or a parenthesized expression. */
+    // TODO: make explicit once effects input Exprs.
+    GrGLSLExpr(const char expr[]) {
+        if (nullptr == expr) {  // TODO: remove this once effects input Exprs.
+            fType = kOnes_ExprType;
+        } else {
+            fType = kFullExpr_ExprType;
+            fExpr = expr;
+        }
+        SkASSERT(this->isValid());
+    }
+
+    /** Constructs an expression from a string.
+     * Argument expr is a simple expression or a parenthesized expression. */
+    // TODO: make explicit once effects input Exprs.
+    GrGLSLExpr(const SkString& expr) {
+        if (expr.isEmpty()) {  // TODO: remove this once effects input Exprs.
+            fType = kOnes_ExprType;
+        } else {
+            fType = kFullExpr_ExprType;
+            fExpr = expr;
+        }
+        SkASSERT(this->isValid());
+    }
+
+    /** Constructs an expression from a string with one substitution. */
+    GrGLSLExpr(const char format[], const char in0[])
+        : fType(kFullExpr_ExprType) {
+        fExpr.appendf(format, in0);
+    }
+
+    /** Constructs an expression from a string with two substitutions. */
+    GrGLSLExpr(const char format[], const char in0[], const char in1[])
+        : fType(kFullExpr_ExprType) {
+        fExpr.appendf(format, in0, in1);
+    }
+
+    /** Returns expression casted to another type.
+     * Generic implementation that is called for non-trivial cases of casts. */
+    template <typename T>
+    static Self VectorCastImpl(const T& other);
+
+    /** Returns a GLSL multiplication: component-wise or component-by-scalar.
+     * The multiplication will be component-wise or multiply each component by a scalar.
+     *
+     * The returned expression will compute the value of:
+     *    vecN(in0.x * in1.x, ...) if dim(T0) == dim(T1) (component-wise)
+     *    vecN(in0.x * in1, ...) if dim(T1) == 1 (vector by scalar)
+     *    vecN(in0 * in1.x, ...) if dim(T0) == 1 (scalar by vector)
+     */
+    template <typename T0, typename T1>
+    static Self Mul(T0 in0, T1 in1);
+
+    /** Returns a GLSL addition: component-wise or add a scalar to each component.
+     * Return value computes:
+     *   vecN(in0.x + in1.x, ...) or vecN(in0.x + in1, ...) or vecN(in0 + in1.x, ...).
+     */
+    template <typename T0, typename T1>
+    static Self Add(T0 in0, T1 in1);
+
+    /** Returns a GLSL subtraction: component-wise or subtract compoments by a scalar.
+     * Return value computes
+     *   vecN(in0.x - in1.x, ...) or vecN(in0.x - in1, ...) or vecN(in0 - in1.x, ...).
+     */
+    template <typename T0, typename T1>
+    static Self Sub(T0 in0, T1 in1);
+
+    /** Returns expression that accesses component(s) of the expression.
+     * format should be the form "%s.x" where 'x' is the component(s) to access.
+     * Caller is responsible for making sure the amount of components in the
+     * format string is equal to dim(T).
+     */
+    template <typename T>
+    T extractComponents(const char format[]) const;
+
+private:
+    enum ExprType {
+        kZeros_ExprType,
+        kOnes_ExprType,
+        kFullExpr_ExprType,
+    };
+    ExprType fType;
+    SkString fExpr;
+};
+
+class GrGLSLExpr1;
+class GrGLSLExpr4;
+
+/** Class representing a float GLSL expression. */
+class GrGLSLExpr1 : public GrGLSLExpr<GrGLSLExpr1> {
+public:
+    GrGLSLExpr1()
+        : INHERITED() {
+    }
+    explicit GrGLSLExpr1(int v)
+        : INHERITED(v) {
+    }
+    GrGLSLExpr1(const char* expr)
+        : INHERITED(expr) {
+    }
+    GrGLSLExpr1(const SkString& expr)
+        : INHERITED(expr) {
+    }
+
+    static GrGLSLExpr1 VectorCast(const GrGLSLExpr1& expr);
+
+private:
+    GrGLSLExpr1(const char format[], const char in0[])
+        : INHERITED(format, in0) {
+    }
+    GrGLSLExpr1(const char format[], const char in0[], const char in1[])
+        : INHERITED(format, in0, in1) {
+    }
+
+    static const char* ZerosStr();
+    static const char* OnesStr();
+    static const char* CastStr();
+    static const char* CastIntStr();
+
+    friend GrGLSLExpr1 operator*(const GrGLSLExpr1& in0, const GrGLSLExpr1&in1);
+    friend GrGLSLExpr1 operator+(const GrGLSLExpr1& in0, const GrGLSLExpr1&in1);
+    friend GrGLSLExpr1 operator-(const GrGLSLExpr1& in0, const GrGLSLExpr1&in1);
+
+    friend class GrGLSLExpr<GrGLSLExpr1>;
+    friend class GrGLSLExpr<GrGLSLExpr4>;
+
+    typedef GrGLSLExpr<GrGLSLExpr1> INHERITED;
+};
+
+/** Class representing a float vector (vec4) GLSL expression. */
+class GrGLSLExpr4 : public GrGLSLExpr<GrGLSLExpr4> {
+public:
+    GrGLSLExpr4()
+        : INHERITED() {
+    }
+    explicit GrGLSLExpr4(int v)
+        : INHERITED(v) {
+    }
+    GrGLSLExpr4(const char* expr)
+        : INHERITED(expr) {
+    }
+    GrGLSLExpr4(const SkString& expr)
+        : INHERITED(expr) {
+    }
+
+    typedef GrGLSLExpr1 AExpr;
+    AExpr a() const;
+
+    /** GLSL vec4 cast / constructor, eg vec4(floatv) -> vec4(floatv, floatv, floatv, floatv) */
+    static GrGLSLExpr4 VectorCast(const GrGLSLExpr1& expr);
+    static GrGLSLExpr4 VectorCast(const GrGLSLExpr4& expr);
+
+private:
+    GrGLSLExpr4(const char format[], const char in0[])
+        : INHERITED(format, in0) {
+    }
+    GrGLSLExpr4(const char format[], const char in0[], const char in1[])
+        : INHERITED(format, in0, in1) {
+    }
+
+    static const char* ZerosStr();
+    static const char* OnesStr();
+    static const char* CastStr();
+    static const char* CastIntStr();
+
+    // The vector-by-scalar and scalar-by-vector binary operations.
+    friend GrGLSLExpr4 operator*(const GrGLSLExpr1& in0, const GrGLSLExpr4&in1);
+    friend GrGLSLExpr4 operator+(const GrGLSLExpr1& in0, const GrGLSLExpr4&in1);
+    friend GrGLSLExpr4 operator-(const GrGLSLExpr1& in0, const GrGLSLExpr4&in1);
+    friend GrGLSLExpr4 operator*(const GrGLSLExpr4& in0, const GrGLSLExpr1&in1);
+    friend GrGLSLExpr4 operator+(const GrGLSLExpr4& in0, const GrGLSLExpr1&in1);
+    friend GrGLSLExpr4 operator-(const GrGLSLExpr4& in0, const GrGLSLExpr1&in1);
+
+    // The vector-by-vector, i.e. component-wise, binary operations.
+    friend GrGLSLExpr4 operator*(const GrGLSLExpr4& in0, const GrGLSLExpr4&in1);
+    friend GrGLSLExpr4 operator+(const GrGLSLExpr4& in0, const GrGLSLExpr4&in1);
+    friend GrGLSLExpr4 operator-(const GrGLSLExpr4& in0, const GrGLSLExpr4&in1);
+
+    friend class GrGLSLExpr<GrGLSLExpr4>;
+
+    typedef GrGLSLExpr<GrGLSLExpr4> INHERITED;
+};
+
+/**
+ * Does an inplace mul, *=, of vec4VarName by mulFactor.
+ * A semicolon is added after the assignment.
+ */
+void GrGLSLMulVarBy4f(SkString* outAppend, const char* vec4VarName, const GrGLSLExpr4& mulFactor);
+
+#include "GrGLSL_impl.h"
+
+#endif
diff --git a/include/private/GrGLSL_impl.h b/include/private/GrGLSL_impl.h
new file mode 100644
index 0000000000..bdd69cc76b
--- /dev/null
+++ b/include/private/GrGLSL_impl.h
@@ -0,0 +1,175 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrGLSL_impl_DEFINED
+#define GrGLSL_impl_DEFINED
+
+template<typename Self>
+template<typename T>
+inline Self GrGLSLExpr<Self>::VectorCastImpl(const T& expr) {
+    if (expr.isZeros()) {
+        return Self(0);
+    }
+    if (expr.isOnes()) {
+        return Self(1);
+    }
+    return Self(Self::CastStr(), expr.c_str());
+}
+
+template<typename Self>
+template<typename T0, typename T1>
+inline Self GrGLSLExpr<Self>::Mul(T0 in0, T1 in1) {
+    if (in0.isZeros() || in1.isZeros()) {
+        return Self(0);
+    }
+    if (in0.isOnes()) {
+        return Self::VectorCast(in1);
+    }
+    if (in1.isOnes()) {
+        return Self::VectorCast(in0);
+    }
+    return Self("(%s * %s)", in0.c_str(), in1.c_str());
+}
+
+template<typename Self>
+template<typename T0, typename T1>
+inline Self GrGLSLExpr<Self>::Add(T0 in0, T1 in1) {
+    if (in1.isZeros()) {
+        return Self::VectorCast(in0);
+    }
+    if (in0.isZeros()) {
+        return Self::VectorCast(in1);
+    }
+    if (in0.isOnes() && in1.isOnes()) {
+        return Self(2);
+    }
+    return Self("(%s + %s)", in0.c_str(), in1.c_str());
+}
+
+template<typename Self>
+template<typename T0, typename T1>
+inline Self GrGLSLExpr<Self>::Sub(T0 in0, T1 in1) {
+    if (in1.isZeros()) {
+        return Self::VectorCast(in0);
+    }
+    if (in1.isOnes()) {
+        if (in0.isOnes()) {
+            return Self(0);
+        }
+    }
+
+    return Self("(%s - %s)", in0.c_str(), in1.c_str());
+}
+
+template <typename Self>
+template <typename T>
+T GrGLSLExpr<Self>::extractComponents(const char format[]) const {
+    if (this->isZeros()) {
+        return T(0);
+    }
+    if (this->isOnes()) {
+        return T(1);
+    }
+    return T(format, this->c_str());
+}
+
+inline GrGLSLExpr1 GrGLSLExpr1::VectorCast(const GrGLSLExpr1& expr) {
+    return expr;
+}
+
+inline const char* GrGLSLExpr1::ZerosStr() {
+    return "0";
+}
+
+inline const char* GrGLSLExpr1::OnesStr() {
+    return "1.0";
+}
+
+// GrGLSLExpr1::CastStr() is unimplemented because using them is likely an
+// error. This is now caught compile-time.
+
+inline const char* GrGLSLExpr1::CastIntStr() {
+    return "%d";
+}
+
+inline GrGLSLExpr1 operator*(const GrGLSLExpr1& in0, const GrGLSLExpr1& in1) {
+    return GrGLSLExpr1::Mul(in0, in1);
+}
+
+inline GrGLSLExpr1 operator+(const GrGLSLExpr1& in0, const GrGLSLExpr1& in1) {
+    return GrGLSLExpr1::Add(in0, in1);
+}
+
+inline GrGLSLExpr1 operator-(const GrGLSLExpr1& in0, const GrGLSLExpr1& in1) {
+    return GrGLSLExpr1::Sub(in0, in1);
+}
+
+inline const char* GrGLSLExpr4::ZerosStr() {
+    return "vec4(0)";
+}
+
+inline const char* GrGLSLExpr4::OnesStr() {
+    return "vec4(1)";
+}
+
+inline const char* GrGLSLExpr4::CastStr() {
+    return "vec4(%s)";
+}
+
+inline const char* GrGLSLExpr4::CastIntStr() {
+    return "vec4(%d)";
+}
+
+inline GrGLSLExpr4 GrGLSLExpr4::VectorCast(const GrGLSLExpr1& expr) {
+    return INHERITED::VectorCastImpl(expr);
+}
+
+inline GrGLSLExpr4 GrGLSLExpr4::VectorCast(const GrGLSLExpr4& expr) {
+    return expr;
+}
+
+inline GrGLSLExpr4::AExpr GrGLSLExpr4::a() const {
+    return this->extractComponents<GrGLSLExpr4::AExpr>("%s.a");
+}
+
+inline GrGLSLExpr4 operator*(const GrGLSLExpr1& in0, const GrGLSLExpr4& in1) {
+    return GrGLSLExpr4::Mul(in0, in1);
+}
+
+inline GrGLSLExpr4 operator+(const GrGLSLExpr1& in0, const GrGLSLExpr4& in1) {
+    return GrGLSLExpr4::Add(in0, in1);
+}
+
+inline GrGLSLExpr4 operator-(const GrGLSLExpr1& in0, const GrGLSLExpr4& in1) {
+    return GrGLSLExpr4::Sub(in0, in1);
+}
+
+inline GrGLSLExpr4 operator*(const GrGLSLExpr4& in0, const GrGLSLExpr1& in1) {
+    return GrGLSLExpr4::Mul(in0, in1);
+}
+
+inline GrGLSLExpr4 operator+(const GrGLSLExpr4& in0, const GrGLSLExpr1& in1) {
+    return GrGLSLExpr4::Add(in0, in1);
+}
+
+inline GrGLSLExpr4 operator-(const GrGLSLExpr4& in0, const GrGLSLExpr1& in1) {
+    return GrGLSLExpr4::Sub(in0, in1);
+}
+
+inline GrGLSLExpr4 operator*(const GrGLSLExpr4& in0, const GrGLSLExpr4& in1) {
+    return GrGLSLExpr4::Mul(in0, in1);
+}
+
+inline GrGLSLExpr4 operator+(const GrGLSLExpr4& in0, const GrGLSLExpr4& in1) {
+    return GrGLSLExpr4::Add(in0, in1);
+}
+
+inline GrGLSLExpr4 operator-(const GrGLSLExpr4& in0, const GrGLSLExpr4& in1) {
+    return GrGLSLExpr4::Sub(in0, in1);
+}
+
+#endif
diff --git a/include/private/GrSwizzle.h b/include/private/GrSwizzle.h
new file mode 100644
index 0000000000..5fa39dd987
--- /dev/null
+++ b/include/private/GrSwizzle.h
@@ -0,0 +1,115 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrSwizzle_DEFINED
+#define GrSwizzle_DEFINED
+
+#include "GrColor.h"
+#include "SkRandom.h"
+
+/** Represents a rgba swizzle. It can be converted either into a string or a eight bit int.
+    Currently there is no way to specify an arbitrary swizzle, just some static swizzles and an
+    assignment operator. That could be relaxed. */
+class GrSwizzle {
+private:
+    char fSwiz[5];
+    uint8_t fKey;
+
+    static constexpr int CToI(char c) {
+        return ('r' == c) ? (GrColor_SHIFT_R / 8) :
+               ('g' == c) ? (GrColor_SHIFT_G / 8) :
+               ('b' == c) ? (GrColor_SHIFT_B / 8) :
+               ('a' == c) ? (GrColor_SHIFT_A / 8) : -1;
+    }
+
+    static constexpr char IToC(int idx) {
+        return (8 * idx) == GrColor_SHIFT_R ? 'r' :
+               (8 * idx) == GrColor_SHIFT_G ? 'g' :
+               (8 * idx) == GrColor_SHIFT_B ? 'b' :
+               (8 * idx) == GrColor_SHIFT_A ? 'a' : 'x';
+    }
+
+    constexpr GrSwizzle(const char c[4])
+        : fSwiz{c[0], c[1], c[2], c[3], 0}
+        , fKey((CToI(c[0]) << 0) | (CToI(c[1]) << 2) | (CToI(c[2]) << 4) | (CToI(c[3]) << 6)) {}
+
+    GR_STATIC_ASSERT(sizeof(char[4]) == sizeof(uint32_t));
+    uint32_t* asUIntPtr() { return SkTCast<uint32_t*>(fSwiz); }
+    uint32_t asUInt() const { return *SkTCast<const uint32_t*>(fSwiz); }
+
+public:
+    GrSwizzle() { *this = RGBA(); }
+
+    GrSwizzle(const GrSwizzle& that) { *this = that; }
+
+    GrSwizzle& operator=(const GrSwizzle& that) {
+        memcpy(this, &that, sizeof(GrSwizzle));
+        return *this;
+    }
+
+    /** Recreates a GrSwizzle from the output of asKey() */
+    void setFromKey(uint8_t key) {
+        fKey = key;
+        for (int i = 0; i < 4; ++i) {
+            fSwiz[i] = IToC(key & 3);
+            key >>= 2;
+        }
+        SkASSERT(fSwiz[4] == 0);
+    }
+
+    bool operator==(const GrSwizzle& that) const { return this->asUInt() == that.asUInt(); }
+
+    bool operator!=(const GrSwizzle& that) const { return !(*this == that); }
+
+    /** Compact representation of the swizzle suitable for a key. */
+    uint8_t asKey() const { return fKey; }
+
+    /** 4 char null terminated string consisting only of chars 'r', 'g', 'b', 'a'. */
+    const char* c_str() const { return fSwiz; }
+
+    /** Applies this swizzle to the input color and returns the swizzled color. */
+    GrColor applyTo(GrColor color) const {
+        int idx;
+        uint32_t key = fKey;
+        // Index of the input color that should be mapped to output r.
+        idx = (key & 3);
+        uint32_t outR = (color >> idx * 8)  & 0xFF;
+        key >>= 2;
+        idx = (key & 3);
+        uint32_t outG = (color >> idx * 8)  & 0xFF;
+        key >>= 2;
+        idx = (key & 3);
+        uint32_t outB = (color >> idx * 8)  & 0xFF;
+        key >>= 2;
+        idx = (key & 3);
+        uint32_t outA = (color >> idx * 8)  & 0xFF;
+        return GrColorPackRGBA(outR, outG, outB, outA);
+    }
+
+    static GrSwizzle RGBA() { return GrSwizzle("rgba"); }
+    static GrSwizzle AAAA() { return GrSwizzle("aaaa"); }
+    static GrSwizzle RRRR() { return GrSwizzle("rrrr"); }
+    static GrSwizzle BGRA() { return GrSwizzle("bgra"); }
+
+    static GrSwizzle CreateRandom(SkRandom* random) {
+        switch (random->nextU() % 4) {
+            case 0:
+                return RGBA();
+            case 1:
+                return BGRA();
+            case 2:
+                return RRRR();
+            case 3:
+                return AAAA();
+            default:
+                SkFAIL("Mod is broken?!?");
+                return RGBA();
+        }
+    }
+};
+
+#endif