gpu/glsl/GrGLSLFragmentShaderBuilder.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 GrGLSLFragmentShaderBuilder_DEFINED
#define GrGLSLFragmentShaderBuilder_DEFINED

#include "GrBlend.h"
#include "GrGLSLShaderBuilder.h"
#include "GrProcessor.h"

class GrRenderTarget;
class GrGLSLVarying;

/*
 * This base class encapsulates the common functionality which all processors use to build fragment
 * shaders.
 */
class GrGLSLFragmentBuilder : public GrGLSLShaderBuilder {
public:
    GrGLSLFragmentBuilder(GrGLSLProgramBuilder* program) : INHERITED(program) {}
    virtual ~GrGLSLFragmentBuilder() {}

    /**
     * Use of these features may require a GLSL extension to be enabled. Shaders may not compile
     * if code is added that uses one of these features without calling enableFeature()
     */
    enum GLSLFeature {
        kMultisampleInterpolation_GLSLFeature
    };

    /**
     * If the feature is supported then true is returned and any necessary #extension declarations
     * are added to the shaders. If the feature is not supported then false will be returned.
     */
    virtual bool enableFeature(GLSLFeature) = 0;

    /**
     * This returns a variable name to access the 2D, perspective correct version of the coords in
     * the fragment shader. The passed in coordinates must either be of type kHalf2 or kHalf3. If
     * the coordinates are 3-dimensional, it a perspective divide into is emitted into the
     * fragment shader (xy / z) to convert them to 2D.
     */
    virtual SkString ensureCoords2D(const GrShaderVar&) = 0;

    // TODO: remove this method.
    void declAppendf(const char* fmt, ...);

private:
    typedef GrGLSLShaderBuilder INHERITED;
};

/*
 * This class is used by fragment processors to build their fragment code.
 */
class GrGLSLFPFragmentBuilder : virtual public GrGLSLFragmentBuilder {
public:
    /** Appease the compiler; the derived class initializes GrGLSLFragmentBuilder. */
    GrGLSLFPFragmentBuilder() : GrGLSLFragmentBuilder(nullptr) {}

    enum Coordinates {
        kSkiaDevice_Coordinates,
        kGLSLWindow_Coordinates,

        kLast_Coordinates = kGLSLWindow_Coordinates
    };

    /**
     * Appends the offset from the center of the pixel to a specified sample.
     *
     * @param sampleIdx      GLSL expression of the sample index.
     * @param Coordinates    Coordinate space in which to emit the offset.
     *
     * A processor must call setWillUseSampleLocations in its constructor before using this method.
     */
    virtual void appendOffsetToSample(const char* sampleIdx, Coordinates) = 0;

    /**
     * Subtracts sample coverage from the fragment. Any sample whose corresponding bit is not found
     * in the mask will not be written out to the framebuffer.
     *
     * @param mask      int that contains the sample mask. Bit N corresponds to the Nth sample.
     * @param invert    perform a bit-wise NOT on the provided mask before applying it?
     *
     * Requires GLSL support for sample variables.
     */
    virtual void maskSampleCoverage(const char* mask, bool invert = false) = 0;

    /**
     * Fragment procs with child procs should call these functions before/after calling emitCode
     * on a child proc.
     */
    virtual void onBeforeChildProcEmitCode() = 0;
    virtual void onAfterChildProcEmitCode() = 0;

    virtual const SkString& getMangleString() const = 0;

    virtual void forceHighPrecision() = 0;
};

/*
 * This class is used by primitive processors to build their fragment code.
 */
class GrGLSLPPFragmentBuilder : public GrGLSLFPFragmentBuilder {
public:
    /** Appease the compiler; the derived class initializes GrGLSLFragmentBuilder. */
    GrGLSLPPFragmentBuilder() : GrGLSLFragmentBuilder(nullptr) {}

    /**
     * Overrides the fragment's sample coverage. The provided mask determines which samples will now
     * be written out to the framebuffer. Note that this mask can be reduced by a future call to
     * maskSampleCoverage.
     *
     * If a primitive processor uses this method, it must guarantee that every codepath through the
     * shader overrides the sample mask at some point.
     *
     * @param mask    int that contains the new coverage mask. Bit N corresponds to the Nth sample.
     *
     * Requires NV_sample_mask_override_coverage.
     */
    virtual void overrideSampleCoverage(const char* mask) = 0;
};

/*
 * This class is used by Xfer processors to build their fragment code.
 */
class GrGLSLXPFragmentBuilder : virtual public GrGLSLFragmentBuilder {
public:
    /** Appease the compiler; the derived class initializes GrGLSLFragmentBuilder. */
    GrGLSLXPFragmentBuilder() : GrGLSLFragmentBuilder(nullptr) {}

    virtual bool hasCustomColorOutput() const = 0;
    virtual bool hasSecondaryOutput() const = 0;

    /** Returns the variable name that holds the color of the destination pixel. This may be nullptr
     * if 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;
};

/*
 * This class implements the various fragment builder interfaces.
 */
class GrGLSLFragmentShaderBuilder : public GrGLSLPPFragmentBuilder, public GrGLSLXPFragmentBuilder {
public:
   /** Returns a nonzero key for a surface's origin. This should only be called if a processor will
       use the fragment position and/or sample locations. */
    static uint8_t KeyForSurfaceOrigin(GrSurfaceOrigin);

    GrGLSLFragmentShaderBuilder(GrGLSLProgramBuilder* program);

    // Shared GrGLSLFragmentBuilder interface.
    bool enableFeature(GLSLFeature) override;
    virtual SkString ensureCoords2D(const GrShaderVar&) override;

    // GrGLSLFPFragmentBuilder interface.
    void appendOffsetToSample(const char* sampleIdx, Coordinates) override;
    void maskSampleCoverage(const char* mask, bool invert = false) override;
    void overrideSampleCoverage(const char* mask) override;
    const SkString& getMangleString() const override { return fMangleString; }
    void onBeforeChildProcEmitCode() override;
    void onAfterChildProcEmitCode() override;
    void forceHighPrecision() override { fForceHighPrecision = true; }

    // GrGLSLXPFragmentBuilder interface.
    bool hasCustomColorOutput() const override { return fHasCustomColorOutput; }
    bool hasSecondaryOutput() const override { return fHasSecondaryOutput; }
    const char* dstColor() override;
    void enableAdvancedBlendEquationIfNeeded(GrBlendEquation) override;

private:
    // Private public interface, used by GrGLProgramBuilder to build a fragment shader
    void enableCustomOutput();
    void enableSecondaryOutput();
    const char* getPrimaryColorOutputName() const;
    const char* getSecondaryColorOutputName() const;
    bool primaryColorOutputIsInOut() const;

#ifdef SK_DEBUG
    // As GLSLProcessors emit code, there are some conditions we need to verify.  We use the below
    // state to track this.  The reset call is called per processor emitted.
    GrProcessor::RequiredFeatures usedProcessorFeatures() const { return fUsedProcessorFeatures; }
    bool hasReadDstColor() const { return fHasReadDstColor; }
    void resetVerification() {
        fUsedProcessorFeatures = GrProcessor::kNone_RequiredFeatures;
        fHasReadDstColor = false;
    }
#endif

    static const char* DeclaredColorOutputName() { return "sk_FragColor"; }
    static const char* DeclaredSecondaryColorOutputName() { return "fsSecondaryColorOut"; }

    GrSurfaceOrigin getSurfaceOrigin() const;

    void onFinalize() override;
    void defineSampleOffsetArray(const char* name, const SkMatrix&);

    static const char* kDstColorName;

    /*
     * State that tracks which child proc in the proc tree is currently emitting code.  This is
     * used to update the fMangleString, which is used to mangle the names of uniforms and functions
     * emitted by the proc.  fSubstageIndices is a stack: its count indicates how many levels deep
     * we are in the tree, and its second-to-last value is the index of the child proc at that
     * level which is currently emitting code. For example, if fSubstageIndices = [3, 1, 2, 0], that
     * means we're currently emitting code for the base proc's 3rd child's 1st child's 2nd child.
     */
    SkTArray<int> fSubstageIndices;

    /*
     * The mangle string is used to mangle the names of uniforms/functions emitted by the child
     * procs so no duplicate uniforms/functions appear in the generated shader program. The mangle
     * string is simply based on fSubstageIndices. For example, if fSubstageIndices = [3, 1, 2, 0],
     * then the manglestring will be "_c3_c1_c2", and any uniform/function emitted by that proc will
     * have "_c3_c1_c2" appended to its name, which can be interpreted as "base proc's 3rd child's
     * 1st child's 2nd child".
     */
    SkString fMangleString;

    bool          fSetupFragPosition;
    bool          fHasCustomColorOutput;
    int           fCustomColorOutputIndex;
    bool          fHasSecondaryOutput;
    uint8_t       fUsedSampleOffsetArrays;
    bool          fHasInitializedSampleMask;
    bool          fForceHighPrecision;

#ifdef SK_DEBUG
    // some state to verify shaders and effects are consistent, this is reset between effects by
    // the program creator
    GrProcessor::RequiredFeatures fUsedProcessorFeatures;
    bool fHasReadDstColor;
#endif

    friend class GrGLSLProgramBuilder;
    friend class GrGLProgramBuilder;
};

#endif