src/effects/gradients/SkGradientShaderPriv.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 SkGradientShaderPriv_DEFINED
#define SkGradientShaderPriv_DEFINED

#include "SkGradientShader.h"
#include "SkClampRange.h"
#include "SkColorPriv.h"
#include "SkMallocPixelRef.h"
#include "SkUnitMapper.h"
#include "SkUtils.h"
#include "SkTemplates.h"
#include "SkBitmapCache.h"
#include "SkShader.h"
#include "GrSamplerState.h"
#include "SkGr.h"
#include "gl/GrGLProgramStage.h"

#ifndef SK_DISABLE_DITHER_32BIT_GRADIENT
    #define USE_DITHER_32BIT_GRADIENT
#endif

static void sk_memset32_dither(uint32_t dst[], uint32_t v0, uint32_t v1,
                               int count) {
    if (count > 0) {
        if (v0 == v1) {
            sk_memset32(dst, v0, count);
        } else {
            int pairs = count >> 1;
            for (int i = 0; i < pairs; i++) {
                *dst++ = v0;
                *dst++ = v1;
            }
            if (count & 1) {
                *dst = v0;
            }
        }
    }
}

//  Clamp

static SkFixed clamp_tileproc(SkFixed x) {
    return SkClampMax(x, 0xFFFF);
}

// Repeat

static SkFixed repeat_tileproc(SkFixed x) {
    return x & 0xFFFF;
}

// Mirror

// Visual Studio 2010 (MSC_VER=1600) optimizes bit-shift code incorrectly.
// See http://code.google.com/p/skia/issues/detail?id=472
#if defined(_MSC_VER) && (_MSC_VER >= 1600)
#pragma optimize("", off)
#endif

static inline SkFixed mirror_tileproc(SkFixed x) {
    int s = x << 15 >> 31;
    return (x ^ s) & 0xFFFF;
}

#if defined(_MSC_VER) && (_MSC_VER >= 1600)
#pragma optimize("", on)
#endif

///////////////////////////////////////////////////////////////////////////////

typedef SkFixed (*TileProc)(SkFixed);

///////////////////////////////////////////////////////////////////////////////

static const TileProc gTileProcs[] = {
    clamp_tileproc,
    repeat_tileproc,
    mirror_tileproc
};

///////////////////////////////////////////////////////////////////////////////

class SkGradientShaderBase : public SkShader {
public:
    SkGradientShaderBase(const SkColor colors[], const SkScalar pos[],
                int colorCount, SkShader::TileMode mode, SkUnitMapper* mapper);
    virtual ~SkGradientShaderBase();

    // overrides
    virtual bool setContext(const SkBitmap&, const SkPaint&, const SkMatrix&) SK_OVERRIDE;
    virtual uint32_t getFlags() SK_OVERRIDE { return fFlags; }
    virtual bool isOpaque() const SK_OVERRIDE;

    void getGradientTableBitmap(SkBitmap*) const;

    enum {
        /// Seems like enough for visual accuracy. TODO: if pos[] deserves
        /// it, use a larger cache.
        kCache16Bits    = 8,
        kGradient16Length = (1 << kCache16Bits),
        /// Each cache gets 1 extra entry at the end so we don't have to
        /// test for end-of-cache in lerps. This is also the value used
        /// to stride *writes* into the dither cache; it must not be zero.
        /// Total space for a cache is 2x kCache16Count entries: one
        /// regular cache, one for dithering.
        kCache16Count   = kGradient16Length + 1,
        kCache16Shift   = 16 - kCache16Bits,
        kSqrt16Shift    = 8 - kCache16Bits,

        /// Seems like enough for visual accuracy. TODO: if pos[] deserves
        /// it, use a larger cache.
        kCache32Bits    = 8,
        kGradient32Length = (1 << kCache32Bits),
        /// Each cache gets 1 extra entry at the end so we don't have to
        /// test for end-of-cache in lerps. This is also the value used
        /// to stride *writes* into the dither cache; it must not be zero.
        /// Total space for a cache is 2x kCache32Count entries: one
        /// regular cache, one for dithering.
        kCache32Count   = kGradient32Length + 1,
        kCache32Shift   = 16 - kCache32Bits,
        kSqrt32Shift    = 8 - kCache32Bits,

        /// This value is used to *read* the dither cache; it may be 0
        /// if dithering is disabled.
#ifdef USE_DITHER_32BIT_GRADIENT
        kDitherStride32 = kCache32Count,
#else
        kDitherStride32 = 0,
#endif
        kDitherStride16 = kCache16Count,
        kLerpRemainderMask32 = (1 << (16 - kCache32Bits)) - 1
    };


protected:
    SkGradientShaderBase(SkFlattenableReadBuffer& );
    virtual void flatten(SkFlattenableWriteBuffer&) const SK_OVERRIDE;

    SkUnitMapper* fMapper;
    SkMatrix    fPtsToUnit;     // set by subclass
    SkMatrix    fDstToIndex;
    SkMatrix::MapXYProc fDstToIndexProc;
    TileMode    fTileMode;
    TileProc    fTileProc;
    int         fColorCount;
    uint8_t     fDstToIndexClass;
    uint8_t     fFlags;

    struct Rec {
        SkFixed     fPos;   // 0...1
        uint32_t    fScale; // (1 << 24) / range
    };
    Rec*        fRecs;

    const uint16_t*     getCache16() const;
    const SkPMColor*    getCache32() const;

    void commonAsAGradient(GradientInfo*) const;

private:
    enum {
        kColorStorageCount = 4, // more than this many colors, and we'll use sk_malloc for the space

        kStorageSize = kColorStorageCount * (sizeof(SkColor) + sizeof(Rec))
    };
    SkColor     fStorage[(kStorageSize + 3) >> 2];
    SkColor*    fOrigColors; // original colors, before modulation by paint in setContext
    bool        fColorsAreOpaque;

    mutable uint16_t*   fCache16;   // working ptr. If this is NULL, we need to recompute the cache values
    mutable SkPMColor*  fCache32;   // working ptr. If this is NULL, we need to recompute the cache values

    mutable uint16_t*   fCache16Storage;    // storage for fCache16, allocated on demand
    mutable SkMallocPixelRef* fCache32PixelRef;
    mutable unsigned    fCacheAlpha;        // the alpha value we used when we computed the cache. larger than 8bits so we can store uninitialized value

    static void Build16bitCache(uint16_t[], SkColor c0, SkColor c1, int count);
    static void Build32bitCache(SkPMColor[], SkColor c0, SkColor c1, int count,
                                U8CPU alpha);
    void setCacheAlpha(U8CPU alpha) const;
    void initCommon();

    typedef SkShader INHERITED;
};

///////////////////////////////////////////////////////////////////////////////

class GrSamplerState;
class GrProgramStageFactory;

/*
 * The intepretation of the texture matrix depends on the sample mode. The
 * texture matrix is applied both when the texture coordinates are explicit
 * and  when vertex positions are used as texture  coordinates. In the latter
 * case the texture matrix is applied to the pre-view-matrix position 
 * values.
 *
 * Normal SampleMode
 *  The post-matrix texture coordinates are in normalize space with (0,0) at
 *  the top-left and (1,1) at the bottom right.
 * RadialGradient
 *  The matrix specifies the radial gradient parameters.
 *  (0,0) in the post-matrix space is center of the radial gradient.
 * Radial2Gradient
 *   Matrix transforms to space where first circle is centered at the
 *   origin. The second circle will be centered (x, 0) where x may be 
 *   0 and is provided by setRadial2Params. The post-matrix space is 
 *   normalized such that 1 is the second radius - first radius.
 * SweepGradient
 *  The angle from the origin of texture coordinates in post-matrix space
 *  determines the gradient value.
 */

// Base class for Gr gradient effects
class GrGradientEffect : public GrCustomStage {
public:

    // FIXME: This constructor is only used in GrGpuGL_unittest.cpp, and should
    // be removed once an alternative testing setup has been devised.
    GrGradientEffect(GrTexture* texture);
    GrGradientEffect(GrContext* ctx, const SkGradientShaderBase& shader, 
                     GrSamplerState* sampler);

    virtual ~GrGradientEffect();

    unsigned int numTextures() const;
    GrTexture* texture(unsigned int index) const;

    bool useTexture() const { return fUseTexture; }

private:

    GrTexture* fTexture;
    bool fUseTexture;

    typedef GrCustomStage INHERITED;

};

///////////////////////////////////////////////////////////////////////////////

// Base class for GL gradient custom stages
class GrGLGradientStage : public GrGLProgramStage {
public:

    GrGLGradientStage(const GrProgramStageFactory& factory);
    virtual ~GrGLGradientStage();

    // emit code that gets a fragment's color from an expression for t; for now
    // this always uses the texture, but for simpler cases we'll be able to lerp
    void emitColorLookup(GrGLShaderBuilder* builder, const char* t, 
                         const char* outputColor, const char* samplerName);

private:

    typedef GrGLProgramStage INHERITED;
};

#endif