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 specific order defined below. 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.
#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))

/**
 * Assert in debug builds that a GrColor is premultiplied.
 */
static inline void GrColorIsPMAssert(GrColor c) {
#ifdef SK_DEBUG
    unsigned a = GrColorUnpackA(c);
    unsigned r = GrColorUnpackR(c);
    unsigned g = GrColorUnpackG(c);
    unsigned b = GrColorUnpackB(c);

    SkASSERT(r <= a);
    SkASSERT(g <= a);
    SkASSERT(b <= a);
#endif
}

/** 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;
}

/**
 * Flags used for bitfields of color components. They are defined so that the bit order reflects the
 * GrColor shift order.
 */
enum GrColorComponentFlags {
    kR_GrColorComponentFlag = 1 << (GrColor_SHIFT_R / 8),
    kG_GrColorComponentFlag = 1 << (GrColor_SHIFT_G / 8),
    kB_GrColorComponentFlag = 1 << (GrColor_SHIFT_B / 8),
    kA_GrColorComponentFlag = 1 << (GrColor_SHIFT_A / 8),

    kRGB_GrColorComponentFlags = (kR_GrColorComponentFlag | kG_GrColorComponentFlag |
                                  kB_GrColorComponentFlag),

    kRGBA_GrColorComponentFlags = (kR_GrColorComponentFlag | kG_GrColorComponentFlag |
                                   kB_GrColorComponentFlag | kA_GrColorComponentFlag)
};

static inline char GrColorComponentFlagToChar(GrColorComponentFlags component) {
    SkASSERT(SkIsPow2(component));
    switch (component) {
        case kR_GrColorComponentFlag:
            return 'r';
        case kG_GrColorComponentFlag:
            return 'g';
        case kB_GrColorComponentFlag:
            return 'b';
        case kA_GrColorComponentFlag:
            return 'a';
        default:
            SkFAIL("Invalid color component flag.");
            return '\0';
    }
}

static inline uint32_t GrPixelConfigComponentMask(GrPixelConfig config) {
    SkASSERT(config >= 0 && config < kGrPixelConfigCnt);
    static const uint32_t kFlags[] = {
        0,                              // kUnknown_GrPixelConfig
        kA_GrColorComponentFlag,        // kAlpha_8_GrPixelConfig
        kRGBA_GrColorComponentFlags,    // kIndex_8_GrPixelConfig
        kRGB_GrColorComponentFlags,     // kRGB_565_GrPixelConfig
        kRGBA_GrColorComponentFlags,    // kRGBA_4444_GrPixelConfig
        kRGBA_GrColorComponentFlags,    // kRGBA_8888_GrPixelConfig
        kRGBA_GrColorComponentFlags,    // kBGRA_8888_GrPixelConfig
        kRGB_GrColorComponentFlags,     // kETC1_GrPixelConfig
        kA_GrColorComponentFlag,        // kLATC_GrPixelConfig
        kA_GrColorComponentFlag,        // kR11_EAC_GrPixelConfig
    };
    return kFlags[config];

    GR_STATIC_ASSERT(0 == kUnknown_GrPixelConfig);
    GR_STATIC_ASSERT(1 == kAlpha_8_GrPixelConfig);
    GR_STATIC_ASSERT(2 == kIndex_8_GrPixelConfig);
    GR_STATIC_ASSERT(3 == kRGB_565_GrPixelConfig);
    GR_STATIC_ASSERT(4 == kRGBA_4444_GrPixelConfig);
    GR_STATIC_ASSERT(5 == kRGBA_8888_GrPixelConfig);
    GR_STATIC_ASSERT(6 == kBGRA_8888_GrPixelConfig);
    GR_STATIC_ASSERT(7 == kETC1_GrPixelConfig);
    GR_STATIC_ASSERT(8 == kLATC_GrPixelConfig);
    GR_STATIC_ASSERT(9 == kR11_EAC_GrPixelConfig);
    GR_STATIC_ASSERT(SK_ARRAY_COUNT(kFlags) == kGrPixelConfigCnt);
}

#endif