src/gpu/effects/GrTextureDomain.h

/*
 * Copyright 2012 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef GrTextureDomain_DEFINED
#define GrTextureDomain_DEFINED

#include "src/gpu/GrCoordTransform.h"
#include "src/gpu/GrFragmentProcessor.h"
#include "src/gpu/glsl/GrGLSLFragmentProcessor.h"
#include "src/gpu/glsl/GrGLSLProgramDataManager.h"

class GrGLProgramBuilder;
class GrGLSLShaderBuilder;
class GrInvariantOutput;
class GrGLSLUniformHandler;
struct SkRect;

/**
 * Limits a texture's lookup coordinates to a domain. Samples outside the domain are either clamped
 * the edge of the domain or result in a half4 of zeros (decal mode). The domain is clipped to
 * normalized texture coords ([0,1]x[0,1] square). Bilinear filtering can cause texels outside the
 * domain to affect the read value unless the caller considers this when calculating the domain.
 */
class GrTextureDomain {
public:
    enum Mode {
        // Ignore the texture domain rectangle.
        kIgnore_Mode,
        // Clamp texture coords to the domain rectangle.
        kClamp_Mode,
        // Treat the area outside the domain rectangle as fully transparent.
        kDecal_Mode,
        // Wrap texture coordinates.  NOTE: filtering may not work as expected because Bilerp will
        // read texels outside of the domain.  We could perform additional texture reads and filter
        // in the shader, but are not currently doing this for performance reasons
        kRepeat_Mode,
        // Mirror wrap texture coordinates. NOTE: suffers the same filtering limitation as kRepeat.
        kMirrorRepeat_Mode,

        kLastMode = kMirrorRepeat_Mode
    };
    static const int kModeCount = kLastMode + 1;

    static const GrTextureDomain& IgnoredDomain() {
        static const GrTextureDomain gDomain((GrTextureProxy*)nullptr,
                                             SkRect::MakeEmpty(), kIgnore_Mode, kIgnore_Mode);
        return gDomain;
    }

    /**
     * Construct a domain used to sample a GrFragmentProcessor.
     *
     * @param index     Pass a value >= 0 if using multiple texture domains in the same effect.
     *                  It is used to keep inserted variables from causing name collisions.
     */
    GrTextureDomain(const SkRect& domain, Mode modeX, Mode modeY, int index = -1);

    /**
     * Construct a domain used to directly sampler a texture.
     *
     * @param index     Pass a value >= 0 if using multiple texture domains in the same effect.
     *                  It is used to keep inserted variables from causing name collisions.
     */
    GrTextureDomain(GrSurfaceProxy*, const SkRect& domain, Mode modeX, Mode modeY, int index = -1);

    GrTextureDomain(const GrTextureDomain&) = default;

    const SkRect& domain() const { return fDomain; }
    Mode modeX() const { return fModeX; }
    Mode modeY() const { return fModeY; }

    /*
     * Computes a domain that bounds all the texels in texelRect, possibly insetting by half a pixel
     * depending on the mode. The mode is used for both axes.
     */
    static const SkRect MakeTexelDomain(const SkIRect& texelRect, Mode mode) {
        return MakeTexelDomain(texelRect, mode, mode);
    }

    static const SkRect MakeTexelDomain(const SkIRect& texelRect, Mode modeX, Mode modeY) {
        // For Clamp and decal modes, inset by half a texel
        SkScalar insetX = ((modeX == kClamp_Mode || modeX == kDecal_Mode) && texelRect.width() > 0)
                ? SK_ScalarHalf : 0;
        SkScalar insetY = ((modeY == kClamp_Mode || modeY == kDecal_Mode) && texelRect.height() > 0)
                ? SK_ScalarHalf : 0;
        return SkRect::MakeLTRB(texelRect.fLeft + insetX, texelRect.fTop + insetY,
                                texelRect.fRight - insetX, texelRect.fBottom - insetY);
    }

    // Convenience to determine if any axis of a texture uses an explicit decal mode or the hardware
    // clamp to border decal mode.
    static bool IsDecalSampled(GrSamplerState::WrapMode wrapX, GrSamplerState::WrapMode wrapY,
                               Mode modeX, Mode modeY) {
        return wrapX == GrSamplerState::WrapMode::kClampToBorder ||
               wrapY == GrSamplerState::WrapMode::kClampToBorder ||
               modeX == kDecal_Mode ||
               modeY == kDecal_Mode;
    }

    static bool IsDecalSampled(const GrSamplerState::WrapMode wraps[2], Mode modeX, Mode modeY) {
        return IsDecalSampled(wraps[0], wraps[1], modeX, modeY);
    }

    static bool IsDecalSampled(GrSamplerState sampler, Mode modeX, Mode modeY) {
        return IsDecalSampled(sampler.wrapModeX(), sampler.wrapModeY(), modeX, modeY);
    }

    bool operator==(const GrTextureDomain& that) const {
        return fModeX == that.fModeX && fModeY == that.fModeY &&
               (kIgnore_Mode == fModeX || (fDomain.fLeft == that.fDomain.fLeft &&
                                           fDomain.fRight == that.fDomain.fRight)) &&
               (kIgnore_Mode == fModeY || (fDomain.fTop == that.fDomain.fTop &&
                                           fDomain.fBottom == that.fDomain.fBottom));
    }
    bool operator!=(const GrTextureDomain& that) const { return !(*this == that); }

    /**
     * A GrGLSLFragmentProcessor subclass that corresponds to a GrProcessor subclass that uses
     * GrTextureDomain should include this helper. It generates the texture domain GLSL, produces
     * the part of the effect key that reflects the texture domain code, and performs the uniform
     * uploads necessary for texture domains.
     */
    class GLDomain {
    public:
        GLDomain() = default;

        /**
         * Call this from GrGLSLFragmentProcessor::emitCode() to sample a child processor WRT the
         * domain and mode.
         *
         * @param outcolor  name of half4 variable to hold the sampled color.
         * @param inCoords  name of float2 variable containing the coords to be used with the
         *                  domain.
         * @param inColor   color passed to the child processor.
         */
        void sampleProcessor(const GrTextureDomain& textureDomain,
                             const char* inColor,
                             const char* outColor,
                             const SkString& inCoords,
                             GrGLSLFragmentProcessor* parent,
                             GrGLSLFragmentProcessor::EmitArgs& args,
                             int childIndex);

        /**
         * Call this from GrGLSLFragmentProcessor::emitCode() to sample the texture WRT the domain
         * and mode.
         *
         * @param outcolor  name of half4 variable to hold the sampled color.
         * @param inCoords  name of float2 variable containing the coords to be used with the
         *                  domain.
         * @param inModulateColor   if non-nullptr the sampled color will be modulated with this
         *                          expression before being written to outColor.
         */
        void sampleTexture(GrGLSLShaderBuilder* builder,
                           GrGLSLUniformHandler* uniformHandler,
                           const GrShaderCaps* shaderCaps,
                           const GrTextureDomain& textureDomain,
                           const char* outColor,
                           const SkString& inCoords,
                           GrGLSLFragmentProcessor::SamplerHandle sampler,
                           const char* inModulateColor = nullptr);

        /**
         * Call this from GrGLSLFragmentProcessor::setData() to upload uniforms necessary for the
         * domain. 'filterIfDecal' determines whether the transition to transparent black at the
         * edge of domain is linearly interpolated over a unit interval or is "hard" when
         * kDecal_Mode is used.
         */
        void setData(const GrGLSLProgramDataManager&, const GrTextureDomain&, bool filterIfDecal);

        /**
         * Call this from GrGLSLFragmentProcessor::setData() to upload uniforms necessary for the
         * texture domain used with a texture proxy. The rectangle is automatically adjusted to
         * account for the texture's origin. Filtering at the edge of the domain is inferred from
         * the GrSamplerState's filter mode.
         */
        void setData(const GrGLSLProgramDataManager&, const GrTextureDomain&,
                     const GrSurfaceProxyView&, GrSamplerState state);
        /** Same as above but with direct control over decal filtering. */
        void setData(const GrGLSLProgramDataManager&, const GrTextureDomain&, const GrSurfaceProxy*,
                     GrSurfaceOrigin, bool filterIfDecal);

        enum {
            kModeBits = 3,  // See DomainKey().
            kDomainKeyBits = 4
        };

        /**
         * GrGLSLFragmentProcessor::GenKey() must call this and include the returned value in it's
         * computed key. The returned will be limited to the lower kDomainKeyBits bits.
         */
        static uint32_t DomainKey(const GrTextureDomain& domain) {
            static_assert(kModeCount <= (1 << kModeBits));
            return domain.modeX() | (domain.modeY() << kModeBits);
        }

    private:
        // Takes a builder and a coord and appends to the builder a string that is an expression
        // the evaluates to a half4 color.
        using AppendSample = SkString(const char* coord);

        void sample(GrGLSLShaderBuilder* builder,
                    GrGLSLUniformHandler* uniformHandler,
                    const GrTextureDomain& textureDomain,
                    const char* outColor,
                    const SkString& inCoords,
                    const std::function<AppendSample>& color);

        SkDEBUGCODE(Mode                        fModeX;)
        SkDEBUGCODE(Mode                        fModeY;)
        SkDEBUGCODE(bool                        fHasMode = false;)
        GrGLSLProgramDataManager::UniformHandle fDomainUni;
        SkString                                fDomainName;

        // Only initialized if the domain has at least one decal axis
        GrGLSLProgramDataManager::UniformHandle fDecalUni;
        SkString                                fDecalName;

        float                                   fPrevDomain[4] = {SK_FloatNaN};
        float                                   fPrevDeclFilterWeights[3] = {SK_FloatNaN};
    };

protected:
    SkRect  fDomain;
    Mode    fModeX;
    Mode    fModeY;
    int     fIndex;
};

#endif