msdfgen/skia/include/private/GrColor.h

/*
 * Copyright 2010 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */



#ifndef GrColor_DEFINED
#define GrColor_DEFINED

#include "SkColor.h"
#include "SkColorData.h"
#include "SkColorPriv.h"
#include "SkHalf.h"

/**
 * GrColor is 4 bytes for R, G, B, A, in a specific order defined below. Whether the color is
 * premultiplied or not depends on the context in which it is being used.
 */
typedef uint32_t GrColor;

// shift amount to assign a component to a GrColor int
// These shift values are chosen for compatibility with GL attrib arrays
// ES doesn't allow BGRA vertex attrib order so if they were not in this order
// we'd have to swizzle in shaders.
#ifdef SK_CPU_BENDIAN
    #define GrColor_SHIFT_R     24
    #define GrColor_SHIFT_G     16
    #define GrColor_SHIFT_B     8
    #define GrColor_SHIFT_A     0
#else
    #define GrColor_SHIFT_R     0
    #define GrColor_SHIFT_G     8
    #define GrColor_SHIFT_B     16
    #define GrColor_SHIFT_A     24
#endif

/**
 *  Pack 4 components (RGBA) into a GrColor int
 */
static inline GrColor GrColorPackRGBA(unsigned r, unsigned g, unsigned b, unsigned a) {
    SkASSERT((uint8_t)r == r);
    SkASSERT((uint8_t)g == g);
    SkASSERT((uint8_t)b == b);
    SkASSERT((uint8_t)a == a);
    return  (r << GrColor_SHIFT_R) |
            (g << GrColor_SHIFT_G) |
            (b << GrColor_SHIFT_B) |
            (a << GrColor_SHIFT_A);
}

// extract a component (byte) from a GrColor int

#define GrColorUnpackR(color)   (((color) >> GrColor_SHIFT_R) & 0xFF)
#define GrColorUnpackG(color)   (((color) >> GrColor_SHIFT_G) & 0xFF)
#define GrColorUnpackB(color)   (((color) >> GrColor_SHIFT_B) & 0xFF)
#define GrColorUnpackA(color)   (((color) >> GrColor_SHIFT_A) & 0xFF)

/**
 *  Since premultiplied means that alpha >= color, we construct a color with
 *  each component==255 and alpha == 0 to be "illegal"
 */
#define GrColor_ILLEGAL     (~(0xFF << GrColor_SHIFT_A))

#define GrColor_WHITE 0xFFFFFFFF

/** Normalizes and coverts an uint8_t to a float. [0, 255] -> [0.0, 1.0] */
static inline float GrNormalizeByteToFloat(uint8_t value) {
    static const float ONE_OVER_255 = 1.f / 255.f;
    return value * ONE_OVER_255;
}

/** Returns true if all channels are in [0, 1]. Used to pick vertex attribute types. */
static inline bool SkPMColor4fFitsInBytes(const SkPMColor4f& color) {
    SkASSERT(color.fA >= 0.0f && color.fA <= 1.0f);
    return color.fR >= 0.0f && color.fR <= 1.0f &&
           color.fG >= 0.0f && color.fG <= 1.0f &&
           color.fB >= 0.0f && color.fB <= 1.0f;
}

/**
 * GrVertexColor is a helper for writing colors to a vertex attribute. It stores either GrColor
 * or four half-float channels, depending on the wideColor parameter. GrVertexWriter will write
 * the correct amount of data. Note that the GP needs to have been constructed with the correct
 * attribute type for colors, to match the usage here.
 */
class GrVertexColor {
public:
    explicit GrVertexColor(const SkPMColor4f& color, bool wideColor)
            : fWideColor(wideColor) {
        if (wideColor) {
            SkFloatToHalf_finite_ftz(Sk4f::Load(color.vec())).store(&fColor);
        } else {
            fColor[0] = color.toBytes_RGBA();
        }
    }

private:
    friend struct GrVertexWriter;

    uint32_t fColor[2];
    bool     fWideColor;
};

#endif