src/gpu/gl/builders/GrGLShaderBuilder.h

/*
 * Copyright 2014 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef GrGLShaderBuilder_DEFINED
#define GrGLShaderBuilder_DEFINED

#include "GrAllocator.h"
#include "glsl/GrGLSLShaderVar.h"
#include "SkTDArray.h"

#include <stdarg.h>

class GrGLProgramBuilder;
class GrGLSLTextureSampler;

/**
  base class for all shaders builders
*/
class GrGLShaderBuilder {
public:
    GrGLShaderBuilder(GrGLProgramBuilder* program);
    virtual ~GrGLShaderBuilder() {}

    void addInput(const GrGLSLShaderVar& input) { fInputs.push_back(input); }
    void addOutput(const GrGLSLShaderVar& output) { fOutputs.push_back(output); }

    /*
     * We put texture lookups in the base class because it is TECHNICALLY possible to do texture
     * lookups in any kind of shader.  However, for the time being using these calls on non-fragment
     * shaders will result in a shader compilation error as texture sampler uniforms are only
     * visible to the fragment shader.  It would not be hard to change this behavior, if someone
     * actually wants to do texture lookups in a non-fragment shader
     *
     * TODO if append texture lookup is used on a non-fragment shader, sampler uniforms should be
     * made visible to that shaders
     */
    /** Appends a 2D texture sample with projection if necessary. coordType must either be Vec2f or
        Vec3f. The latter is interpreted as projective texture coords. The vec length and swizzle
        order of the result depends on the GrTextureAccess associated with the GrGLSLTextureSampler.
        */
    void appendTextureLookup(SkString* out,
                             const GrGLSLTextureSampler&,
                             const char* coordName,
                             GrSLType coordType = kVec2f_GrSLType) const;

    /** Version of above that appends the result to the fragment shader code instead.*/
    void appendTextureLookup(const GrGLSLTextureSampler&,
                             const char* coordName,
                             GrSLType coordType = kVec2f_GrSLType);


    /** Does the work of appendTextureLookup and modulates the result by modulation. The result is
        always a vec4. modulation and the swizzle specified by GrGLSLTextureSampler must both be
        vec4 or float. If modulation is "" or nullptr it this function acts as though
        appendTextureLookup were called. */
    void appendTextureLookupAndModulate(const char* modulation,
                                        const GrGLSLTextureSampler&,
                                        const char* coordName,
                                        GrSLType coordType = kVec2f_GrSLType);

    /**
    * Called by GrGLProcessors to add code to one of the shaders.
    */
    void codeAppendf(const char format[], ...) SK_PRINTF_LIKE(2, 3) {
       va_list args;
       va_start(args, format);
       this->code().appendVAList(format, args);
       va_end(args);
    }

    void codeAppend(const char* str) { this->code().append(str); }

    void codePrependf(const char format[], ...) SK_PRINTF_LIKE(2, 3) {
       va_list args;
       va_start(args, format);
       this->code().prependVAList(format, args);
       va_end(args);
    }

    /**
     * Appends a variable declaration to one of the shaders
     */
    void declAppend(const GrGLSLShaderVar& var);

    /** Emits a helper function outside of main() in the fragment shader. */
    void emitFunction(GrSLType returnType,
                      const char* name,
                      int argCnt,
                      const GrGLSLShaderVar* args,
                      const char* body,
                      SkString* outName);

    /*
     * Combines the various parts of the shader to create a single finalized shader string.
     */
    void finalize(uint32_t visibility);

    /*
     * Get parent builder for adding uniforms
     */
    GrGLProgramBuilder* getProgramBuilder() { return fProgramBuilder; }

    /**
     * Helper for begining and ending a block in the shader code.
     */
    class ShaderBlock {
    public:
        ShaderBlock(GrGLShaderBuilder* builder) : fBuilder(builder) {
            SkASSERT(builder);
            fBuilder->codeAppend("{");
        }

        ~ShaderBlock() {
            fBuilder->codeAppend("}");
        }
    private:
        GrGLShaderBuilder* fBuilder;
    };

protected:
    typedef GrTAllocator<GrGLSLShaderVar> VarArray;
    void appendDecls(const VarArray& vars, SkString* out) const;

    /*
     * this super low level function is just for use internally to builders
     */
    void appendTextureLookup(const char* samplerName,
                             const char* coordName,
                             uint32_t configComponentMask,
                             const char* swizzle);

    /*
     * A general function which enables an extension in a shader if the feature bit is not present
     */
    void addFeature(uint32_t featureBit, const char* extensionName);

    enum InterfaceQualifier {
        kOut_InterfaceQualifier,
        kLastInterfaceQualifier = kOut_InterfaceQualifier
    };

    /*
     * A low level function to build default layout qualifiers.
     *
     *   e.g. layout(param1, param2, ...) out;
     *
     * GLSL allows default layout qualifiers for in, out, and uniform.
     */
    void addLayoutQualifier(const char* param, InterfaceQualifier);

    void compileAndAppendLayoutQualifiers();

    void nextStage() {
        fShaderStrings.push_back();
        fCompilerStrings.push_back(this->code().c_str());
        fCompilerStringLengths.push_back((int)this->code().size());
        fCodeIndex++;
    }

    SkString& versionDecl() { return fShaderStrings[kVersionDecl]; }
    SkString& extensions() { return fShaderStrings[kExtensions]; }
    SkString& precisionQualifier() { return fShaderStrings[kPrecisionQualifier]; }
    SkString& layoutQualifiers() { return fShaderStrings[kLayoutQualifiers]; }
    SkString& uniforms() { return fShaderStrings[kUniforms]; }
    SkString& inputs() { return fShaderStrings[kInputs]; }
    SkString& outputs() { return fShaderStrings[kOutputs]; }
    SkString& functions() { return fShaderStrings[kFunctions]; }
    SkString& main() { return fShaderStrings[kMain]; }
    SkString& code() { return fShaderStrings[fCodeIndex]; }

    virtual void onFinalize() = 0;

    enum {
        kVersionDecl,
        kExtensions,
        kPrecisionQualifier,
        kLayoutQualifiers,
        kUniforms,
        kInputs,
        kOutputs,
        kFunctions,
        kMain,
        kCode,
    };

    GrGLProgramBuilder* fProgramBuilder;
    SkSTArray<kCode, const char*, true> fCompilerStrings;
    SkSTArray<kCode, int, true> fCompilerStringLengths;
    SkSTArray<kCode, SkString> fShaderStrings;
    SkString fCode;
    SkString fFunctions;
    SkString fExtensions;

    VarArray fInputs;
    VarArray fOutputs;
    uint32_t fFeaturesAddedMask;
    SkSTArray<1, SkString> fLayoutParams[kLastInterfaceQualifier + 1];
    int fCodeIndex;
    bool fFinalized;

    friend class GrGLProgramBuilder;
    friend class GrGLPathProgramBuilder; // to access fInputs.
};
#endif