skia2/include/gpu/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 "GrTypes.h"

/**
 *  GrColor is 4 bytes for R, G, B, A, in a compile-time specific order. The
 *  components are stored premultiplied.
 */
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. Note the assumption that the cpu is little
// endian.
#define GrColor_SHIFT_R     0
#define GrColor_SHIFT_G     8
#define GrColor_SHIFT_B     16
#define GrColor_SHIFT_A     24

/**
 *  Pack 4 components (RGBA) into a GrColor int
 */
static inline GrColor GrColorPackRGBA(unsigned r, unsigned g,
                                      unsigned b, unsigned a) {
    GrAssert((uint8_t)r == r);
    GrAssert((uint8_t)g == g);
    GrAssert((uint8_t)b == b);
    GrAssert((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))

/** Converts a GrColor to an rgba array of GrGLfloat */
static inline void GrColorToRGBAFloat(GrColor color, float rgba[4]) {
    static const float ONE_OVER_255 = 1.f / 255.f;
    rgba[0] = GrColorUnpackR(color) * ONE_OVER_255;
    rgba[1] = GrColorUnpackG(color) * ONE_OVER_255;
    rgba[2] = GrColorUnpackB(color) * ONE_OVER_255;
    rgba[3] = GrColorUnpackA(color) * ONE_OVER_255;
}

#endif