src/gpu/gl/GrGLProgram.cpp

/*
 * Copyright 2011 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "GrGLProgram.h"

#include "GrAllocator.h"
#include "GrCustomStage.h"
#include "GrGLProgramStage.h"
#include "gl/GrGLShaderBuilder.h"
#include "GrGLShaderVar.h"
#include "GrProgramStageFactory.h"
#include "SkTrace.h"
#include "SkXfermode.h"

SK_DEFINE_INST_COUNT(GrGLProgram)

#define GL_CALL(X) GR_GL_CALL(fContextInfo.interface(), X)
#define GL_CALL_RET(R, X) GR_GL_CALL_RET(fContextInfo.interface(), R, X)

namespace {

enum {
    /// Used to mark a StageUniLocation field that should be bound
    /// to a uniform during getUniformLocationsAndInitCache().
    kUseUniform = 2000
};

}  // namespace

#define PRINT_SHADERS 0

typedef GrGLProgram::Desc::StageDesc StageDesc;

#define VIEW_MATRIX_NAME "uViewM"

#define POS_ATTR_NAME "aPosition"
#define COL_ATTR_NAME "aColor"
#define COV_ATTR_NAME "aCoverage"
#define EDGE_ATTR_NAME "aEdge"
#define COL_UNI_NAME "uColor"
#define COV_UNI_NAME "uCoverage"
#define COL_FILTER_UNI_NAME "uColorFilter"
#define COL_MATRIX_UNI_NAME "uColorMatrix"
#define COL_MATRIX_VEC_UNI_NAME "uColorMatrixVec"

namespace {
inline void tex_attr_name(int coordIdx, SkString* s) {
    *s = "aTexCoord";
    s->appendS32(coordIdx);
}

inline const char* float_vector_type_str(int count) {
    return GrGLShaderVar::TypeString(GrSLFloatVectorType(count));
}

inline const char* vector_all_coords(int count) {
    static const char* ALL[] = {"ERROR", "", ".xy", ".xyz", ".xyzw"};
    GrAssert(count >= 1 && count < (int)GR_ARRAY_COUNT(ALL));
    return ALL[count];
}

inline const char* all_ones_vec(int count) {
    static const char* ONESVEC[] = {"ERROR", "1.0", "vec2(1,1)",
                                    "vec3(1,1,1)", "vec4(1,1,1,1)"};
    GrAssert(count >= 1 && count < (int)GR_ARRAY_COUNT(ONESVEC));
    return ONESVEC[count];
}

inline const char* all_zeros_vec(int count) {
    static const char* ZEROSVEC[] = {"ERROR", "0.0", "vec2(0,0)",
                                    "vec3(0,0,0)", "vec4(0,0,0,0)"};
    GrAssert(count >= 1 && count < (int)GR_ARRAY_COUNT(ZEROSVEC));
    return ZEROSVEC[count];
}

inline const char* declared_color_output_name() { return "fsColorOut"; }
inline const char* dual_source_output_name() { return "dualSourceOut"; }

inline void tex_matrix_name(int stage, SkString* s) {
    *s = "uTexM";
    s->appendS32(stage);
}

inline void sampler_name(int stage, SkString* s) {
    *s = "uSampler";
    s->appendS32(stage);
}
}

GrGLProgram* GrGLProgram::Create(const GrGLContextInfo& gl,
                                 const Desc& desc,
                                 GrCustomStage** customStages) {
    GrGLProgram* program = SkNEW_ARGS(GrGLProgram, (gl, desc, customStages));
    if (!program->succeeded()) {
        delete program;
        program = NULL;
    }
    return program;
}

GrGLProgram::GrGLProgram(const GrGLContextInfo& gl,
                         const Desc& desc,
                         GrCustomStage** customStages) : fContextInfo(gl) {
    fDesc = desc;
    fVShaderID = 0;
    fGShaderID = 0;
    fFShaderID = 0;
    fProgramID = 0;
    for (int s = 0; s < GrDrawState::kNumStages; ++s) {
        fProgramStage[s] = NULL;
    }
    this->genProgram(customStages);
}

GrGLProgram::~GrGLProgram() {
    if (fVShaderID) {
        GL_CALL(DeleteShader(fVShaderID));
    }
    if (fGShaderID) {
        GL_CALL(DeleteShader(fGShaderID));
    }
    if (fFShaderID) {
        GL_CALL(DeleteShader(fFShaderID));
    }
    if (fProgramID) {
        GL_CALL(DeleteProgram(fProgramID));
    }

    for (int i = 0; i < GrDrawState::kNumStages; ++i) {
        delete fProgramStage[i];
    }
}

void GrGLProgram::abandon() {
    fVShaderID = 0;
    fGShaderID = 0;
    fFShaderID = 0;
    fProgramID = 0;
}

void GrGLProgram::overrideBlend(GrBlendCoeff* srcCoeff,
                                GrBlendCoeff* dstCoeff) const {
    switch (fDesc.fDualSrcOutput) {
        case Desc::kNone_DualSrcOutput:
            break;
        // the prog will write a coverage value to the secondary
        // output and the dst is blended by one minus that value.
        case Desc::kCoverage_DualSrcOutput:
        case Desc::kCoverageISA_DualSrcOutput:
        case Desc::kCoverageISC_DualSrcOutput:
        *dstCoeff = (GrBlendCoeff)GrGpu::kIS2C_GrBlendCoeff;
        break;
        default:
            GrCrash("Unexpected dual source blend output");
            break;
    }
}

// assigns modulation of two vars to an output var
// vars can be vec4s or floats (or one of each)
// result is always vec4
// if either var is "" then assign to the other var
// if both are "" then assign all ones
static inline void modulate_helper(const char* outputVar,
                                   const char* var0,
                                   const char* var1,
                                   SkString* code) {
    GrAssert(NULL != outputVar);
    GrAssert(NULL != var0);
    GrAssert(NULL != var1);
    GrAssert(NULL != code);

    bool has0 = '\0' != *var0;
    bool has1 = '\0' != *var1;

    if (!has0 && !has1) {
        code->appendf("\t%s = %s;\n", outputVar, all_ones_vec(4));
    } else if (!has0) {
        code->appendf("\t%s = vec4(%s);\n", outputVar, var1);
    } else if (!has1) {
        code->appendf("\t%s = vec4(%s);\n", outputVar, var0);
    } else {
        code->appendf("\t%s = vec4(%s * %s);\n", outputVar, var0, var1);
    }
}

// assigns addition of two vars to an output var
// vars can be vec4s or floats (or one of each)
// result is always vec4
// if either var is "" then assign to the other var
// if both are "" then assign all zeros
static inline void add_helper(const char* outputVar,
                              const char* var0,
                              const char* var1,
                              SkString* code) {
    GrAssert(NULL != outputVar);
    GrAssert(NULL != var0);
    GrAssert(NULL != var1);
    GrAssert(NULL != code);

    bool has0 = '\0' != *var0;
    bool has1 = '\0' != *var1;

    if (!has0 && !has1) {
        code->appendf("\t%s = %s;\n", outputVar, all_zeros_vec(4));
    } else if (!has0) {
        code->appendf("\t%s = vec4(%s);\n", outputVar, var1);
    } else if (!has1) {
        code->appendf("\t%s = vec4(%s);\n", outputVar, var0);
    } else {
        code->appendf("\t%s = vec4(%s + %s);\n", outputVar, var0, var1);
    }
}

// given two blend coeffecients determine whether the src
// and/or dst computation can be omitted.
static inline void needBlendInputs(SkXfermode::Coeff srcCoeff,
                                   SkXfermode::Coeff dstCoeff,
                                   bool* needSrcValue,
                                   bool* needDstValue) {
    if (SkXfermode::kZero_Coeff == srcCoeff) {
        switch (dstCoeff) {
            // these all read the src
            case SkXfermode::kSC_Coeff:
            case SkXfermode::kISC_Coeff:
            case SkXfermode::kSA_Coeff:
            case SkXfermode::kISA_Coeff:
                *needSrcValue = true;
                break;
            default:
                *needSrcValue = false;
                break;
        }
    } else {
        *needSrcValue = true;
    }
    if (SkXfermode::kZero_Coeff == dstCoeff) {
        switch (srcCoeff) {
            // these all read the dst
            case SkXfermode::kDC_Coeff:
            case SkXfermode::kIDC_Coeff:
            case SkXfermode::kDA_Coeff:
            case SkXfermode::kIDA_Coeff:
                *needDstValue = true;
                break;
            default:
                *needDstValue = false;
                break;
        }
    } else {
        *needDstValue = true;
    }
}

/**
 * Create a blend_coeff * value string to be used in shader code. Sets empty
 * string if result is trivially zero.
 */
static void blendTermString(SkString* str, SkXfermode::Coeff coeff,
                             const char* src, const char* dst,
                             const char* value) {
    switch (coeff) {
    case SkXfermode::kZero_Coeff:    /** 0 */
        *str = "";
        break;
    case SkXfermode::kOne_Coeff:     /** 1 */
        *str = value;
        break;
    case SkXfermode::kSC_Coeff:
        str->printf("(%s * %s)", src, value);
        break;
    case SkXfermode::kISC_Coeff:
        str->printf("((%s - %s) * %s)", all_ones_vec(4), src, value);
        break;
    case SkXfermode::kDC_Coeff:
        str->printf("(%s * %s)", dst, value);
        break;
    case SkXfermode::kIDC_Coeff:
        str->printf("((%s - %s) * %s)", all_ones_vec(4), dst, value);
        break;
    case SkXfermode::kSA_Coeff:      /** src alpha */
        str->printf("(%s.a * %s)", src, value);
        break;
    case SkXfermode::kISA_Coeff:     /** inverse src alpha (i.e. 1 - sa) */
        str->printf("((1.0 - %s.a) * %s)", src, value);
        break;
    case SkXfermode::kDA_Coeff:      /** dst alpha */
        str->printf("(%s.a * %s)", dst, value);
        break;
    case SkXfermode::kIDA_Coeff:     /** inverse dst alpha (i.e. 1 - da) */
        str->printf("((1.0 - %s.a) * %s)", dst, value);
        break;
    default:
        GrCrash("Unexpected xfer coeff.");
        break;
    }
}
/**
 * Adds a line to the fragment shader code which modifies the color by
 * the specified color filter.
 */
static void addColorFilter(SkString* fsCode, const char * outputVar,
                           SkXfermode::Coeff uniformCoeff,
                           SkXfermode::Coeff colorCoeff,
                           const char* inColor) {
    SkString colorStr, constStr;
    blendTermString(&colorStr, colorCoeff, COL_FILTER_UNI_NAME,
                    inColor, inColor);
    blendTermString(&constStr, uniformCoeff, COL_FILTER_UNI_NAME,
                    inColor, COL_FILTER_UNI_NAME);

    add_helper(outputVar, colorStr.c_str(), constStr.c_str(), fsCode);
}
/**
 * Adds code to the fragment shader code which modifies the color by
 * the specified color matrix.
 */
static void addColorMatrix(SkString* fsCode, const char * outputVar,
                           const char* inColor) {
    fsCode->appendf("\t%s = %s * vec4(%s.rgb / %s.a, %s.a) + %s;\n", outputVar, COL_MATRIX_UNI_NAME, inColor, inColor, inColor, COL_MATRIX_VEC_UNI_NAME);
    fsCode->appendf("\t%s.rgb *= %s.a;\n", outputVar, outputVar);
}

void GrGLProgram::genEdgeCoverage(SkString* coverageVar,
                                  GrGLShaderBuilder* segments) const {
    if (fDesc.fVertexLayout & GrDrawTarget::kEdge_VertexLayoutBit) {
        const char *vsName, *fsName;
        segments->addVarying(kVec4f_GrSLType, "Edge", &vsName, &fsName);
        segments->fVSAttrs.push_back().set(kVec4f_GrSLType,
            GrGLShaderVar::kAttribute_TypeModifier, EDGE_ATTR_NAME);
        segments->fVSCode.appendf("\t%s = " EDGE_ATTR_NAME ";\n", vsName);
        switch (fDesc.fVertexEdgeType) {
        case GrDrawState::kHairLine_EdgeType:
            segments->fFSCode.appendf("\tfloat edgeAlpha = abs(dot(vec3(gl_FragCoord.xy,1), %s.xyz));\n", fsName);
            segments->fFSCode.append("\tedgeAlpha = max(1.0 - edgeAlpha, 0.0);\n");
            break;
        case GrDrawState::kQuad_EdgeType:
            segments->fFSCode.append("\tfloat edgeAlpha;\n");
            // keep the derivative instructions outside the conditional 
            segments->fFSCode.appendf("\tvec2 duvdx = dFdx(%s.xy);\n", fsName);
            segments->fFSCode.appendf("\tvec2 duvdy = dFdy(%s.xy);\n", fsName);
            segments->fFSCode.appendf("\tif (%s.z > 0.0 && %s.w > 0.0) {\n", fsName, fsName);
            // today we know z and w are in device space. We could use derivatives
            segments->fFSCode.appendf("\t\tedgeAlpha = min(min(%s.z, %s.w) + 0.5, 1.0);\n", fsName, fsName);
            segments->fFSCode.append ("\t} else {\n");
            segments->fFSCode.appendf("\t\tvec2 gF = vec2(2.0*%s.x*duvdx.x - duvdx.y,\n"
                                      "\t\t               2.0*%s.x*duvdy.x - duvdy.y);\n",
                                      fsName, fsName);
            segments->fFSCode.appendf("\t\tedgeAlpha = (%s.x*%s.x - %s.y);\n", fsName, fsName, fsName);
            segments->fFSCode.append("\t\tedgeAlpha = clamp(0.5 - edgeAlpha / length(gF), 0.0, 1.0);\n"
                                      "\t}\n");
            if (kES2_GrGLBinding == fContextInfo.binding()) {
                segments->fHeader.printf("#extension GL_OES_standard_derivatives: enable\n");
            }
            break;
        case GrDrawState::kHairQuad_EdgeType:
            segments->fFSCode.appendf("\tvec2 duvdx = dFdx(%s.xy);\n", fsName);
            segments->fFSCode.appendf("\tvec2 duvdy = dFdy(%s.xy);\n", fsName);
            segments->fFSCode.appendf("\tvec2 gF = vec2(2.0*%s.x*duvdx.x - duvdx.y,\n"
                                      "\t               2.0*%s.x*duvdy.x - duvdy.y);\n",
                                      fsName, fsName);
            segments->fFSCode.appendf("\tfloat edgeAlpha = (%s.x*%s.x - %s.y);\n", fsName, fsName, fsName);
            segments->fFSCode.append("\tedgeAlpha = sqrt(edgeAlpha*edgeAlpha / dot(gF, gF));\n");
            segments->fFSCode.append("\tedgeAlpha = max(1.0 - edgeAlpha, 0.0);\n");
            if (kES2_GrGLBinding == fContextInfo.binding()) {
                segments->fHeader.printf("#extension GL_OES_standard_derivatives: enable\n");
            }
            break;
        case GrDrawState::kCircle_EdgeType:
            segments->fFSCode.append("\tfloat edgeAlpha;\n");
            segments->fFSCode.appendf("\tfloat d = distance(gl_FragCoord.xy, %s.xy);\n", fsName);
            segments->fFSCode.appendf("\tfloat outerAlpha = smoothstep(d - 0.5, d + 0.5, %s.z);\n", fsName);
            segments->fFSCode.appendf("\tfloat innerAlpha = %s.w == 0.0 ? 1.0 : smoothstep(%s.w - 0.5, %s.w + 0.5, d);\n", fsName, fsName, fsName);
            segments->fFSCode.append("\tedgeAlpha = outerAlpha * innerAlpha;\n");
            break;
        default:
            GrCrash("Unknown Edge Type!");
            break;
        }
        *coverageVar = "edgeAlpha";
    } else {
        coverageVar->reset();
    }
}

void GrGLProgram::genInputColor(GrGLShaderBuilder* builder, SkString* inColor) {
    switch (fDesc.fColorInput) {
        case GrGLProgram::Desc::kAttribute_ColorInput: {
            builder->fVSAttrs.push_back().set(kVec4f_GrSLType,
                GrGLShaderVar::kAttribute_TypeModifier,
                COL_ATTR_NAME);
            const char *vsName, *fsName;
            builder->addVarying(kVec4f_GrSLType, "Color", &vsName, &fsName);
            builder->fVSCode.appendf("\t%s = " COL_ATTR_NAME ";\n", vsName);
            *inColor = fsName;
            } break;
        case GrGLProgram::Desc::kUniform_ColorInput:
            builder->addUniform(GrGLShaderBuilder::kFragment_ShaderType,
                                 kVec4f_GrSLType, COL_UNI_NAME);
            fUniLocations.fColorUni = kUseUniform;
            *inColor = COL_UNI_NAME;
            break;
        case GrGLProgram::Desc::kTransBlack_ColorInput:
            GrAssert(!"needComputedColor should be false.");
            break;
        case GrGLProgram::Desc::kSolidWhite_ColorInput:
            break;
        default:
            GrCrash("Unknown color type.");
            break;
    }
}

void GrGLProgram::genUniformCoverage(GrGLShaderBuilder* builder, SkString* inOutCoverage) {
    builder->addUniform(GrGLShaderBuilder::kFragment_ShaderType,
                        kVec4f_GrSLType, COV_UNI_NAME);
    fUniLocations.fCoverageUni = kUseUniform;
    if (inOutCoverage->size()) {
        builder->fFSCode.appendf("\tvec4 uniCoverage = %s * %s;\n",
                                  COV_UNI_NAME, inOutCoverage->c_str());
        *inOutCoverage = "uniCoverage";
    } else {
        *inOutCoverage = COV_UNI_NAME;
    }
}

namespace {
void gen_attribute_coverage(GrGLShaderBuilder* segments,
                            SkString* inOutCoverage) {
    segments->fVSAttrs.push_back().set(kVec4f_GrSLType,
                                       GrGLShaderVar::kAttribute_TypeModifier,
                                       COV_ATTR_NAME);
    const char *vsName, *fsName;
    segments->addVarying(kVec4f_GrSLType, "Coverage", &vsName, &fsName);
    segments->fVSCode.appendf("\t%s = " COV_ATTR_NAME ";\n", vsName);
    if (inOutCoverage->size()) {
        segments->fFSCode.appendf("\tvec4 attrCoverage = %s * %s;\n",
                                  fsName, inOutCoverage->c_str());
        *inOutCoverage = "attrCoverage";
    } else {
        *inOutCoverage = fsName;
    }
}
}

void GrGLProgram::genGeometryShader(GrGLShaderBuilder* segments) const {
#if GR_GL_EXPERIMENTAL_GS
    if (fDesc.fExperimentalGS) {
        GrAssert(fContextInfo.glslGeneration() >= k150_GrGLSLGeneration);
        segments->fGSHeader.append("layout(triangles) in;\n"
                                   "layout(triangle_strip, max_vertices = 6) out;\n");
        segments->fGSCode.append("void main() {\n"
                                 "\tfor (int i = 0; i < 3; ++i) {\n"
                                  "\t\tgl_Position = gl_in[i].gl_Position;\n");
        if (fDesc.fEmitsPointSize) {
            segments->fGSCode.append("\t\tgl_PointSize = 1.0;\n");
        }
        GrAssert(segments->fGSInputs.count() == segments->fGSOutputs.count());
        int count = segments->fGSInputs.count();
        for (int i = 0; i < count; ++i) {
            segments->fGSCode.appendf("\t\t%s = %s[i];\n",
                                      segments->fGSOutputs[i].getName().c_str(),
                                      segments->fGSInputs[i].getName().c_str());
        }
        segments->fGSCode.append("\t\tEmitVertex();\n"
                                 "\t}\n"
                                 "\tEndPrimitive();\n"
                                 "}\n");
    }
#endif
}

const char* GrGLProgram::adjustInColor(const SkString& inColor) const {
    if (inColor.size()) {
          return inColor.c_str();
    } else {
        if (Desc::kSolidWhite_ColorInput == fDesc.fColorInput) {
            return all_ones_vec(4);
        } else {
            return all_zeros_vec(4);
        }
    }
}

namespace {
// prints a shader using params similar to glShaderSource
void print_shader(GrGLint stringCnt,
                  const GrGLchar** strings,
                  GrGLint* stringLengths) {
    for (int i = 0; i < stringCnt; ++i) {
        if (NULL == stringLengths || stringLengths[i] < 0) {
            GrPrintf(strings[i]);
        } else {
            GrPrintf("%.*s", stringLengths[i], strings[i]);
        }
    }
}

// Compiles a GL shader, returns shader ID or 0 if failed params have same meaning as glShaderSource
GrGLuint compile_shader(const GrGLContextInfo& gl,
                        GrGLenum type,
                        int stringCnt,
                        const char** strings,
                        int* stringLengths) {
    SK_TRACE_EVENT1("GrGLProgram::CompileShader",
                    "stringCount", SkStringPrintf("%i", stringCnt).c_str());

    GrGLuint shader;
    GR_GL_CALL_RET(gl.interface(), shader, CreateShader(type));
    if (0 == shader) {
        return 0;
    }

    const GrGLInterface* gli = gl.interface();
    GrGLint compiled = GR_GL_INIT_ZERO;
    GR_GL_CALL(gli, ShaderSource(shader, stringCnt, strings, stringLengths));
    GR_GL_CALL(gli, CompileShader(shader));
    GR_GL_CALL(gli, GetShaderiv(shader, GR_GL_COMPILE_STATUS, &compiled));

    if (!compiled) {
        GrGLint infoLen = GR_GL_INIT_ZERO;
        GR_GL_CALL(gli, GetShaderiv(shader, GR_GL_INFO_LOG_LENGTH, &infoLen));
        SkAutoMalloc log(sizeof(char)*(infoLen+1)); // outside if for debugger
        if (infoLen > 0) {
            // retrieve length even though we don't need it to workaround bug in chrome cmd buffer
            // param validation.
            GrGLsizei length = GR_GL_INIT_ZERO;
            GR_GL_CALL(gli, GetShaderInfoLog(shader, infoLen+1, 
                                             &length, (char*)log.get()));
            print_shader(stringCnt, strings, stringLengths);
            GrPrintf("\n%s", log.get());
        }
        GrAssert(!"Shader compilation failed!");
        GR_GL_CALL(gli, DeleteShader(shader));
        return 0;
    }
    return shader;
}

// helper version of above for when shader is already flattened into a single SkString
GrGLuint compile_shader(const GrGLContextInfo& gl, GrGLenum type, const SkString& shader) {
    const GrGLchar* str = shader.c_str();
    int length = shader.size();
    return compile_shader(gl, type, 1, &str, &length);
}

}

// compiles all the shaders from builder and stores the shader IDs
bool GrGLProgram::compileShaders(const GrGLShaderBuilder& builder) {

    SkString shader;

    builder.getShader(GrGLShaderBuilder::kVertex_ShaderType, &shader);
#if PRINT_SHADERS
    GrPrintf(shader.c_str());
    GrPrintf("\n");
#endif
    if (!(fVShaderID = compile_shader(fContextInfo, GR_GL_VERTEX_SHADER, shader))) {
        return false;
    }

    if (builder.fUsesGS) {
        builder.getShader(GrGLShaderBuilder::kGeometry_ShaderType, &shader);
#if PRINT_SHADERS
        GrPrintf(shader.c_str());
        GrPrintf("\n");
#endif
        if (!(fGShaderID = compile_shader(fContextInfo, GR_GL_GEOMETRY_SHADER, shader))) {
            return false;
        }
    } else {
        fGShaderID = 0;
    }

    builder.getShader(GrGLShaderBuilder::kFragment_ShaderType, &shader);
#if PRINT_SHADERS
    GrPrintf(shader.c_str());
    GrPrintf("\n");
#endif
    if (!(fFShaderID = compile_shader(fContextInfo, GR_GL_FRAGMENT_SHADER, shader))) {
        return false;
    }

    return true;
}


bool GrGLProgram::genProgram(GrCustomStage** customStages) {
    GrAssert(0 == fProgramID);

    GrGLShaderBuilder builder(fContextInfo);
    const uint32_t& layout = fDesc.fVertexLayout;

    fUniLocations.reset();

#if GR_GL_EXPERIMENTAL_GS
    builder.fUsesGS = fDesc.fExperimentalGS;
#endif

    SkXfermode::Coeff colorCoeff, uniformCoeff;
    bool applyColorMatrix = SkToBool(fDesc.fColorMatrixEnabled);
    // The rest of transfer mode color filters have not been implemented
    if (fDesc.fColorFilterXfermode < SkXfermode::kCoeffModesCnt) {
        GR_DEBUGCODE(bool success =)
            SkXfermode::ModeAsCoeff(static_cast<SkXfermode::Mode>
                                    (fDesc.fColorFilterXfermode),
                                    &uniformCoeff, &colorCoeff);
        GR_DEBUGASSERT(success);
    } else {
        colorCoeff = SkXfermode::kOne_Coeff;
        uniformCoeff = SkXfermode::kZero_Coeff;
    }

    // no need to do the color filter / matrix at all if coverage is 0. The
    // output color is scaled by the coverage. All the dual source outputs are
    // scaled by the coverage as well.
    if (Desc::kTransBlack_ColorInput == fDesc.fCoverageInput) {
        colorCoeff = SkXfermode::kZero_Coeff;
        uniformCoeff = SkXfermode::kZero_Coeff;
        applyColorMatrix = false;
    }

    // If we know the final color is going to be all zeros then we can
    // simplify the color filter coeffecients. needComputedColor will then
    // come out false below.
    if (Desc::kTransBlack_ColorInput == fDesc.fColorInput) {
        colorCoeff = SkXfermode::kZero_Coeff;
        if (SkXfermode::kDC_Coeff == uniformCoeff ||
            SkXfermode::kDA_Coeff == uniformCoeff) {
            uniformCoeff = SkXfermode::kZero_Coeff;
        } else if (SkXfermode::kIDC_Coeff == uniformCoeff ||
                   SkXfermode::kIDA_Coeff == uniformCoeff) {
            uniformCoeff = SkXfermode::kOne_Coeff;
        }
    }

    bool needColorFilterUniform;
    bool needComputedColor;
    needBlendInputs(uniformCoeff, colorCoeff,
                    &needColorFilterUniform, &needComputedColor);

    // the dual source output has no canonical var name, have to
    // declare an output, which is incompatible with gl_FragColor/gl_FragData.
    bool dualSourceOutputWritten = false;
    builder.fHeader.append(GrGetGLSLVersionDecl(fContextInfo.binding(),
                                                fContextInfo.glslGeneration()));

    GrGLShaderVar colorOutput;
    bool isColorDeclared = GrGLSLSetupFSColorOuput(fContextInfo.glslGeneration(),
                                                   declared_color_output_name(),
                                                   &colorOutput);
    if (isColorDeclared) {
        builder.fFSOutputs.push_back(colorOutput);
    }

    builder.addUniform(GrGLShaderBuilder::kVertex_ShaderType,
                       kMat33f_GrSLType, VIEW_MATRIX_NAME);
    fUniLocations.fViewMatrixUni = kUseUniform;

    builder.fVSAttrs.push_back().set(kVec2f_GrSLType,
                                     GrGLShaderVar::kAttribute_TypeModifier,
                                     POS_ATTR_NAME);

    builder.fVSCode.append("void main() {\n"
                              "\tvec3 pos3 = " VIEW_MATRIX_NAME " * vec3("POS_ATTR_NAME", 1);\n"
                              "\tgl_Position = vec4(pos3.xy, 0, pos3.z);\n");

    // incoming color to current stage being processed.
    SkString inColor;

    if (needComputedColor) {
        this->genInputColor(&builder, &inColor);
    }

    // we output point size in the GS if present
    if (fDesc.fEmitsPointSize && !builder.fUsesGS){
        builder.fVSCode.append("\tgl_PointSize = 1.0;\n");
    }

    builder.fFSCode.append("void main() {\n");

    // add texture coordinates that are used to the list of vertex attr decls
    SkString texCoordAttrs[GrDrawState::kMaxTexCoords];
    for (int t = 0; t < GrDrawState::kMaxTexCoords; ++t) {
        if (GrDrawTarget::VertexUsesTexCoordIdx(t, layout)) {
            tex_attr_name(t, texCoordAttrs + t);
            builder.fVSAttrs.push_back().set(kVec2f_GrSLType,
                GrGLShaderVar::kAttribute_TypeModifier,
                texCoordAttrs[t].c_str());
        }
    }

    ///////////////////////////////////////////////////////////////////////////
    // compute the final color

    // if we have color stages string them together, feeding the output color
    // of each to the next and generating code for each stage.
    if (needComputedColor) {
        SkString outColor;
        for (int s = 0; s < fDesc.fFirstCoverageStage; ++s) {
            if (fDesc.fStages[s].isEnabled()) {
                // create var to hold stage result
                outColor = "color";
                outColor.appendS32(s);
                builder.fFSCode.appendf("\tvec4 %s;\n", outColor.c_str());

                const char* inCoords;
                // figure out what our input coords are
                int tcIdx = GrDrawTarget::VertexTexCoordsForStage(s, layout);
                if (tcIdx < 0) {
                    inCoords = POS_ATTR_NAME;
                } else {
                    // must have input tex coordinates if stage is enabled.
                    GrAssert(texCoordAttrs[tcIdx].size());
                    inCoords = texCoordAttrs[tcIdx].c_str();
                }

                if (NULL != customStages[s]) {
                    const GrProgramStageFactory& factory = customStages[s]->getFactory();
                    fProgramStage[s] = factory.createGLInstance(*customStages[s]);
                }
                this->genStageCode(s,
                                   inColor.size() ? inColor.c_str() : NULL,
                                   outColor.c_str(),
                                   inCoords,
                                   &builder);
                inColor = outColor;
            }
        }
    }

    // if have all ones or zeros for the "dst" input to the color filter then we
    // may be able to make additional optimizations.
    if (needColorFilterUniform && needComputedColor && !inColor.size()) {
        GrAssert(Desc::kSolidWhite_ColorInput == fDesc.fColorInput);
        bool uniformCoeffIsZero = SkXfermode::kIDC_Coeff == uniformCoeff ||
                                  SkXfermode::kIDA_Coeff == uniformCoeff;
        if (uniformCoeffIsZero) {
            uniformCoeff = SkXfermode::kZero_Coeff;
            bool bogus;
            needBlendInputs(SkXfermode::kZero_Coeff, colorCoeff,
                            &needColorFilterUniform, &bogus);
        }
    }
    if (needColorFilterUniform) {
        builder.addUniform(GrGLShaderBuilder::kFragment_ShaderType,
                           kVec4f_GrSLType, COL_FILTER_UNI_NAME);
        fUniLocations.fColorFilterUni = kUseUniform;
    }
    bool wroteFragColorZero = false;
    if (SkXfermode::kZero_Coeff == uniformCoeff &&
        SkXfermode::kZero_Coeff == colorCoeff &&
        !applyColorMatrix) {
        builder.fFSCode.appendf("\t%s = %s;\n",
                                colorOutput.getName().c_str(),
                                all_zeros_vec(4));
        wroteFragColorZero = true;
    } else if (SkXfermode::kDst_Mode != fDesc.fColorFilterXfermode) {
        builder.fFSCode.append("\tvec4 filteredColor;\n");
        const char* color = adjustInColor(inColor);
        addColorFilter(&builder.fFSCode, "filteredColor", uniformCoeff,
                       colorCoeff, color);
        inColor = "filteredColor";
    }
    if (applyColorMatrix) {
        builder.addUniform(GrGLShaderBuilder::kFragment_ShaderType,
                           kMat44f_GrSLType, COL_MATRIX_UNI_NAME);
        builder.addUniform(GrGLShaderBuilder::kFragment_ShaderType,
                           kVec4f_GrSLType, COL_MATRIX_VEC_UNI_NAME);
        fUniLocations.fColorMatrixUni = kUseUniform;
        fUniLocations.fColorMatrixVecUni = kUseUniform;
        builder.fFSCode.append("\tvec4 matrixedColor;\n");
        const char* color = adjustInColor(inColor);
        addColorMatrix(&builder.fFSCode, "matrixedColor", color);
        inColor = "matrixedColor";
    }

    ///////////////////////////////////////////////////////////////////////////
    // compute the partial coverage (coverage stages and edge aa)

    SkString inCoverage;
    bool coverageIsZero = Desc::kTransBlack_ColorInput == fDesc.fCoverageInput;
    // we don't need to compute coverage at all if we know the final shader
    // output will be zero and we don't have a dual src blend output.
    if (!wroteFragColorZero || Desc::kNone_DualSrcOutput != fDesc.fDualSrcOutput) {

        if (!coverageIsZero) {
            this->genEdgeCoverage(&inCoverage, &builder);

            switch (fDesc.fCoverageInput) {
                case Desc::kSolidWhite_ColorInput:
                    // empty string implies solid white
                    break;
                case Desc::kAttribute_ColorInput:
                    gen_attribute_coverage(&builder, &inCoverage);
                    break;
                case Desc::kUniform_ColorInput:
                    this->genUniformCoverage(&builder, &inCoverage);
                    break;
                default:
                    GrCrash("Unexpected input coverage.");
            }

            SkString outCoverage;
            const int& startStage = fDesc.fFirstCoverageStage;
            for (int s = startStage; s < GrDrawState::kNumStages; ++s) {
                if (fDesc.fStages[s].isEnabled()) {
                    // create var to hold stage output
                    outCoverage = "coverage";
                    outCoverage.appendS32(s);
                    builder.fFSCode.appendf("\tvec4 %s;\n",
                                            outCoverage.c_str());

                    const char* inCoords;
                    // figure out what our input coords are
                    int tcIdx =
                        GrDrawTarget::VertexTexCoordsForStage(s, layout);
                    if (tcIdx < 0) {
                        inCoords = POS_ATTR_NAME;
                    } else {
                        // must have input tex coordinates if stage is
                        // enabled.
                        GrAssert(texCoordAttrs[tcIdx].size());
                        inCoords = texCoordAttrs[tcIdx].c_str();
                    }

                    if (NULL != customStages[s]) {
                        const GrProgramStageFactory& factory = customStages[s]->getFactory();
                        fProgramStage[s] = factory.createGLInstance(*customStages[s]);
                    }
                    this->genStageCode(s,
                                       inCoverage.size() ? inCoverage.c_str() : NULL,
                                       outCoverage.c_str(),
                                       inCoords,
                                       &builder);
                    inCoverage = outCoverage;
                }
            }
        }
        if (Desc::kNone_DualSrcOutput != fDesc.fDualSrcOutput) {
            builder.fFSOutputs.push_back().set(kVec4f_GrSLType,
                                               GrGLShaderVar::kOut_TypeModifier,
                                               dual_source_output_name());
            bool outputIsZero = coverageIsZero;
            SkString coeff;
            if (!outputIsZero &&
                Desc::kCoverage_DualSrcOutput != fDesc.fDualSrcOutput && !wroteFragColorZero) {
                if (!inColor.size()) {
                    outputIsZero = true;
                } else {
                    if (Desc::kCoverageISA_DualSrcOutput == fDesc.fDualSrcOutput) {
                        coeff.printf("(1 - %s.a)", inColor.c_str());
                    } else {
                        coeff.printf("(vec4(1,1,1,1) - %s)", inColor.c_str());
                    }
                }
            }
            if (outputIsZero) {
                builder.fFSCode.appendf("\t%s = %s;\n",
                                        dual_source_output_name(),
                                         all_zeros_vec(4));
            } else {
                modulate_helper(dual_source_output_name(),
                                coeff.c_str(),
                                inCoverage.c_str(),
                                &builder.fFSCode);
            }
            dualSourceOutputWritten = true;
        }
    }

    ///////////////////////////////////////////////////////////////////////////
    // combine color and coverage as frag color

    if (!wroteFragColorZero) {
        if (coverageIsZero) {
            builder.fFSCode.appendf("\t%s = %s;\n",
                                    colorOutput.getName().c_str(),
                                    all_zeros_vec(4));
        } else {
            modulate_helper(colorOutput.getName().c_str(),
                            inColor.c_str(),
                            inCoverage.c_str(),
                            &builder.fFSCode);
        }
        if (Desc::kUnpremultiplied_RoundDown_OutputConfig == fDesc.fOutputConfig) {
            builder.fFSCode.appendf("\t%s = %s.a <= 0.0 ? vec4(0,0,0,0) : vec4(floor(%s.rgb / %s.a * 255.0)/255.0, %s.a);\n",
                                    colorOutput.getName().c_str(),
                                    colorOutput.getName().c_str(),
                                    colorOutput.getName().c_str(),
                                    colorOutput.getName().c_str(),
                                    colorOutput.getName().c_str());
        } else if (Desc::kUnpremultiplied_RoundUp_OutputConfig == fDesc.fOutputConfig) {
            builder.fFSCode.appendf("\t%s = %s.a <= 0.0 ? vec4(0,0,0,0) : vec4(ceil(%s.rgb / %s.a * 255.0)/255.0, %s.a);\n",
                                    colorOutput.getName().c_str(),
                                    colorOutput.getName().c_str(),
                                    colorOutput.getName().c_str(),
                                    colorOutput.getName().c_str(),
                                    colorOutput.getName().c_str());
        }
    }

    builder.fVSCode.append("}\n");
    builder.fFSCode.append("}\n");

    ///////////////////////////////////////////////////////////////////////////
    // insert GS
#if GR_DEBUG
    this->genGeometryShader(&builder);
#endif

    ///////////////////////////////////////////////////////////////////////////
    // compile and setup attribs and unis

    if (!this->compileShaders(builder)) {
        return false;
    }

    if (!this->bindOutputsAttribsAndLinkProgram(texCoordAttrs,
                                                isColorDeclared,
                                                dualSourceOutputWritten)) {
        return false;
    }

    this->getUniformLocationsAndInitCache(builder);

    return true;
}

bool GrGLProgram::bindOutputsAttribsAndLinkProgram(SkString texCoordAttrNames[],
                                                   bool bindColorOut,
                                                   bool bindDualSrcOut) {
    GL_CALL_RET(fProgramID, CreateProgram());
    if (!fProgramID) {
        return false;
    }

    GL_CALL(AttachShader(fProgramID, fVShaderID));
    if (fGShaderID) {
        GL_CALL(AttachShader(fProgramID, fGShaderID));
    }
    GL_CALL(AttachShader(fProgramID, fFShaderID));

    if (bindColorOut) {
        GL_CALL(BindFragDataLocation(fProgramID, 0, declared_color_output_name()));
    }
    if (bindDualSrcOut) {
        GL_CALL(BindFragDataLocationIndexed(fProgramID, 0, 1, dual_source_output_name()));
    }

    // Bind the attrib locations to same values for all shaders
    GL_CALL(BindAttribLocation(fProgramID, PositionAttributeIdx(), POS_ATTR_NAME));
    for (int t = 0; t < GrDrawState::kMaxTexCoords; ++t) {
        if (texCoordAttrNames[t].size()) {
            GL_CALL(BindAttribLocation(fProgramID,
                                       TexCoordAttributeIdx(t),
                                       texCoordAttrNames[t].c_str()));
        }
    }

    GL_CALL(BindAttribLocation(fProgramID, ColorAttributeIdx(), COL_ATTR_NAME));
    GL_CALL(BindAttribLocation(fProgramID, CoverageAttributeIdx(), COV_ATTR_NAME));
    GL_CALL(BindAttribLocation(fProgramID, EdgeAttributeIdx(), EDGE_ATTR_NAME));

    GL_CALL(LinkProgram(fProgramID));

    GrGLint linked = GR_GL_INIT_ZERO;
    GL_CALL(GetProgramiv(fProgramID, GR_GL_LINK_STATUS, &linked));
    if (!linked) {
        GrGLint infoLen = GR_GL_INIT_ZERO;
        GL_CALL(GetProgramiv(fProgramID, GR_GL_INFO_LOG_LENGTH, &infoLen));
        SkAutoMalloc log(sizeof(char)*(infoLen+1));  // outside if for debugger
        if (infoLen > 0) {
            // retrieve length even though we don't need it to workaround
            // bug in chrome cmd buffer param validation.
            GrGLsizei length = GR_GL_INIT_ZERO;
            GL_CALL(GetProgramInfoLog(fProgramID,
                                      infoLen+1,
                                      &length,
                                      (char*)log.get()));
            GrPrintf((char*)log.get());
        }
        GrAssert(!"Error linking program");
        GL_CALL(DeleteProgram(fProgramID));
        fProgramID = 0;
        return false;
    }
    return true;
}

void GrGLProgram::getUniformLocationsAndInitCache(const GrGLShaderBuilder& builder) {

    if (kUseUniform == fUniLocations.fViewMatrixUni) {
        GL_CALL_RET(fUniLocations.fViewMatrixUni, GetUniformLocation(fProgramID, VIEW_MATRIX_NAME));
        GrAssert(kUnusedUniform != fUniLocations.fViewMatrixUni);
    }
    if (kUseUniform == fUniLocations.fColorUni) {
        GL_CALL_RET(fUniLocations.fColorUni, GetUniformLocation(fProgramID, COL_UNI_NAME));
        GrAssert(kUnusedUniform != fUniLocations.fColorUni);
    }
    if (kUseUniform == fUniLocations.fColorFilterUni) {
        GL_CALL_RET(fUniLocations.fColorFilterUni,
                    GetUniformLocation(fProgramID, COL_FILTER_UNI_NAME));
        GrAssert(kUnusedUniform != fUniLocations.fColorFilterUni);
    }

    if (kUseUniform == fUniLocations.fColorMatrixUni) {
        GL_CALL_RET(fUniLocations.fColorMatrixUni,
                    GetUniformLocation(fProgramID, COL_MATRIX_UNI_NAME));
    }

    if (kUseUniform == fUniLocations.fColorMatrixVecUni) {
        GL_CALL_RET(fUniLocations.fColorMatrixVecUni,
                    GetUniformLocation(fProgramID, COL_MATRIX_VEC_UNI_NAME));
    }

    if (kUseUniform == fUniLocations.fCoverageUni) {
        GL_CALL_RET(fUniLocations.fCoverageUni,GetUniformLocation(fProgramID, COV_UNI_NAME));
        GrAssert(kUnusedUniform != fUniLocations.fCoverageUni);
    }

    for (int s = 0; s < GrDrawState::kNumStages; ++s) {
        StageUniLocations& locations = fUniLocations.fStages[s];
        if (fDesc.fStages[s].isEnabled()) {
            if (kUseUniform == locations.fTextureMatrixUni) {
                SkString texMName;
                tex_matrix_name(s, &texMName);
                GL_CALL_RET(locations.fTextureMatrixUni,
                            GetUniformLocation(fProgramID, texMName.c_str()));
                //color filter table effect does not consumer coords gen'ed by matrix.
                //GrAssert(kUnusedUniform != locations.fTextureMatrixUni);
            }

            if (kUseUniform == locations.fSamplerUni) {
                SkString samplerName;
                sampler_name(s, &samplerName);
                GL_CALL_RET(locations.fSamplerUni,
                            GetUniformLocation(fProgramID,samplerName.c_str()));
                GrAssert(kUnusedUniform != locations.fSamplerUni);
            }

            if (NULL != fProgramStage[s]) {
                fProgramStage[s]->initUniforms(&builder, fContextInfo.interface(), fProgramID);
            }
        }
    }
    GL_CALL(UseProgram(fProgramID));

    // init sampler unis and set bogus values for state tracking
    for (int s = 0; s < GrDrawState::kNumStages; ++s) {
        if (kUnusedUniform != fUniLocations.fStages[s].fSamplerUni) {
            GL_CALL(Uniform1i(fUniLocations.fStages[s].fSamplerUni, s));
        }
        fTextureMatrices[s] = GrMatrix::InvalidMatrix();
        // this is arbitrary, just initialize to something
        fTextureOrientation[s] = GrGLTexture::kBottomUp_Orientation;
        // Must not reset fStageOverride[] here.
    }
    fViewMatrix = GrMatrix::InvalidMatrix();
    fViewportSize.set(-1, -1);
    fColor = GrColor_ILLEGAL;
    fColorFilterColor = GrColor_ILLEGAL;
}

///////////////////////////////////////////////////////////////////////////////
// Stage code generation

void GrGLProgram::genStageCode(int stageNum,
                               const char* fsInColor, // NULL means no incoming color
                               const char* fsOutColor,
                               const char* vsInCoord,
                               GrGLShaderBuilder* segments) {
    GrAssert(stageNum >= 0 && stageNum <= GrDrawState::kNumStages);

    const GrGLProgram::StageDesc& desc = fDesc.fStages[stageNum];
    StageUniLocations& locations = fUniLocations.fStages[stageNum];
    GrGLProgramStage* customStage = fProgramStage[stageNum];

    GrAssert((desc.fInConfigFlags & StageDesc::kInConfigBitMask) == desc.fInConfigFlags);

    /// Vertex Shader Stuff

    // decide whether we need a matrix to transform texture coords and whether the varying needs a
    // perspective coord.
    const char* matName = NULL;
    if (desc.fOptFlags & StageDesc::kIdentityMatrix_OptFlagBit) {
        segments->fVaryingDims = segments->fCoordDims;
    } else {
        SkString texMatName;
        tex_matrix_name(stageNum, &texMatName);
        GrGLShaderBuilder::UniformHandle m =
            segments->addUniform(GrGLShaderBuilder::kVertex_ShaderType,
                                 kMat33f_GrSLType, texMatName.c_str());
        const GrGLShaderVar& mat = segments->getUniformVariable(m);
        // Can't use texMatName.c_str() because it's on the stack!
        matName = mat.getName().c_str();
        locations.fTextureMatrixUni = kUseUniform;

        if (desc.fOptFlags & StageDesc::kNoPerspective_OptFlagBit) {
            segments->fVaryingDims = segments->fCoordDims;
        } else {
            segments->fVaryingDims = segments->fCoordDims + 1;
        }
    }
    GrAssert(segments->fVaryingDims > 0);

    // Must setup variables after computing segments->fVaryingDims
    if (NULL != customStage) {
        customStage->setupVariables(segments, stageNum);
    }

    SkString samplerName;
    sampler_name(stageNum, &samplerName);
    segments->addUniform(GrGLShaderBuilder::kFragment_ShaderType,
                         kSampler2D_GrSLType, samplerName.c_str());
    locations.fSamplerUni = kUseUniform;

    const char *varyingVSName, *varyingFSName;
    segments->addVarying(GrSLFloatVectorType(segments->fVaryingDims),
                         "Stage",
                         stageNum,
                         &varyingVSName,
                         &varyingFSName);

    if (!matName) {
        GrAssert(segments->fVaryingDims == segments->fCoordDims);
        segments->fVSCode.appendf("\t%s = %s;\n", varyingVSName, vsInCoord);
    } else {
        // varying = texMatrix * texCoord
        segments->fVSCode.appendf("\t%s = (%s * vec3(%s, 1))%s;\n",
                                  varyingVSName, matName, vsInCoord,
                                  vector_all_coords(segments->fVaryingDims));
    }

    if (NULL != customStage) {
        segments->fVSCode.appendf("\t{ // stage %d %s\n",
                                  stageNum, customStage->name());
        customStage->emitVS(segments, varyingVSName);
        segments->fVSCode.appendf("\t}\n");
    }

    /// Fragment Shader Stuff

    segments->fSampleCoords = varyingFSName;

    GrGLShaderBuilder::SamplerMode sampleMode =
        GrGLShaderBuilder::kExplicitDivide_SamplerMode;
    if (desc.fOptFlags & (StageDesc::kIdentityMatrix_OptFlagBit |
                          StageDesc::kNoPerspective_OptFlagBit)) {
        sampleMode = GrGLShaderBuilder::kDefault_SamplerMode;
    } else if (NULL == customStage) {
        sampleMode = GrGLShaderBuilder::kProj_SamplerMode;
    }
    segments->setupTextureAccess(sampleMode, stageNum);

    segments->computeSwizzle(desc.fInConfigFlags);
    segments->computeModulate(fsInColor);

    static const uint32_t kMulByAlphaMask =
        (StageDesc::kMulRGBByAlpha_RoundUp_InConfigFlag |
         StageDesc::kMulRGBByAlpha_RoundDown_InConfigFlag);

    // NOTE: GrGLProgramStages are now responsible for fetching
    if (NULL == customStage) {
        if (desc.fInConfigFlags & kMulByAlphaMask) {
            // only one of the mul by alpha flags should be set
            GrAssert(GrIsPow2(kMulByAlphaMask & desc.fInConfigFlags));
            GrAssert(!(desc.fInConfigFlags & 
                       StageDesc::kSmearAlpha_InConfigFlag));
            GrAssert(!(desc.fInConfigFlags & 
                       StageDesc::kSmearRed_InConfigFlag));
            segments->fFSCode.appendf("\t%s = %s(%s, %s)%s;\n",
                                      fsOutColor,
                                      segments->fTexFunc.c_str(), 
                                      samplerName.c_str(),
                                      segments->fSampleCoords.c_str(),
                                      segments->fSwizzle.c_str());
            if (desc.fInConfigFlags &
                StageDesc::kMulRGBByAlpha_RoundUp_InConfigFlag) {
                segments->fFSCode.appendf("\t%s = vec4(ceil(%s.rgb*%s.a*255.0)/255.0,%s.a)%s;\n",
                                          fsOutColor, fsOutColor, fsOutColor,
                                          fsOutColor, segments->fModulate.c_str());
            } else {
                segments->fFSCode.appendf("\t%s = vec4(floor(%s.rgb*%s.a*255.0)/255.0,%s.a)%s;\n",
                                          fsOutColor, fsOutColor, fsOutColor,
                                          fsOutColor, segments->fModulate.c_str());
            }
        } else {
            segments->emitDefaultFetch(fsOutColor, samplerName.c_str());
        }
    }

    if (NULL != customStage) {
        // Enclose custom code in a block to avoid namespace conflicts
        segments->fFSCode.appendf("\t{ // stage %d %s \n",
                                  stageNum, customStage->name());
        customStage->emitFS(segments, fsOutColor, fsInColor,
                            samplerName.c_str());
        segments->fFSCode.appendf("\t}\n");
    }
}