src/video/SDL_pixels.c
author Sam Lantinga <slouken@libsdl.org>
Mon, 07 Mar 2011 00:30:05 -0800
changeset 5438 b705640cb34a
parent 5437 ce10653e370c
child 5439 3a778c6c0269
permissions -rw-r--r--
Fixed bitmap order interpretation; SDL defaults to MSB ordering so a bitstream corresponds to a pixel stream. The bitmap ordering is defined such that the numbering refers to the pixel index from left to right, and the number position refers to the bit position in the byte. SDL_BITMAPORDER_4321 is the fourth pixel at the high bit and the first pixel at the low bit (LSBFirst) SDL_BITMAPORDER_1234 is the first pixel at the high bit and the fourth pixel at the low bit (MSBFirst)

/*
    SDL - Simple DirectMedia Layer
    Copyright (C) 1997-2011 Sam Lantinga

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

    Sam Lantinga
    slouken@libsdl.org
*/
#include "SDL_config.h"

/* General (mostly internal) pixel/color manipulation routines for SDL */

#include "SDL_endian.h"
#include "SDL_video.h"
#include "SDL_sysvideo.h"
#include "SDL_blit.h"
#include "SDL_pixels_c.h"
#include "SDL_RLEaccel_c.h"


/* Helper functions */

const char*
SDL_GetPixelFormatName(Uint32 format)
{
    switch (format) {
#define CASE(X) case X: return #X;
    CASE(SDL_PIXELFORMAT_INDEX1LSB)
    CASE(SDL_PIXELFORMAT_INDEX1MSB)
    CASE(SDL_PIXELFORMAT_INDEX4LSB)
    CASE(SDL_PIXELFORMAT_INDEX4MSB)
    CASE(SDL_PIXELFORMAT_INDEX8)
    CASE(SDL_PIXELFORMAT_RGB332)
    CASE(SDL_PIXELFORMAT_RGB444)
    CASE(SDL_PIXELFORMAT_RGB555)
    CASE(SDL_PIXELFORMAT_BGR555)
    CASE(SDL_PIXELFORMAT_ARGB4444)
    CASE(SDL_PIXELFORMAT_RGBA4444)
    CASE(SDL_PIXELFORMAT_ABGR4444)
    CASE(SDL_PIXELFORMAT_BGRA4444)
    CASE(SDL_PIXELFORMAT_ARGB1555)
    CASE(SDL_PIXELFORMAT_RGBA5551)
    CASE(SDL_PIXELFORMAT_ABGR1555)
    CASE(SDL_PIXELFORMAT_BGRA5551)
    CASE(SDL_PIXELFORMAT_RGB565)
    CASE(SDL_PIXELFORMAT_BGR565)
    CASE(SDL_PIXELFORMAT_RGB24)
    CASE(SDL_PIXELFORMAT_BGR24)
    CASE(SDL_PIXELFORMAT_RGB888)
    CASE(SDL_PIXELFORMAT_BGR888)
    CASE(SDL_PIXELFORMAT_ARGB8888)
    CASE(SDL_PIXELFORMAT_RGBA8888)
    CASE(SDL_PIXELFORMAT_ABGR8888)
    CASE(SDL_PIXELFORMAT_BGRA8888)
    CASE(SDL_PIXELFORMAT_ARGB2101010)
    CASE(SDL_PIXELFORMAT_YV12)
    CASE(SDL_PIXELFORMAT_IYUV)
    CASE(SDL_PIXELFORMAT_YUY2)
    CASE(SDL_PIXELFORMAT_UYVY)
    CASE(SDL_PIXELFORMAT_YVYU)
#undef CASE
    default:
        return "SDL_PIXELFORMAT_UNKNOWN";
    }
}

SDL_bool
SDL_PixelFormatEnumToMasks(Uint32 format, int *bpp, Uint32 * Rmask,
                           Uint32 * Gmask, Uint32 * Bmask, Uint32 * Amask)
{
    Uint32 masks[4];

    /* This function doesn't work with FourCC pixel formats */
    if (SDL_ISPIXELFORMAT_FOURCC(format)) {
        SDL_SetError("FOURCC pixel formats are not supported");
        return SDL_FALSE;
    }
 
    /* Initialize the values here */
    if (SDL_BYTESPERPIXEL(format) <= 2) {
        *bpp = SDL_BITSPERPIXEL(format);
    } else {
        *bpp = SDL_BYTESPERPIXEL(format) * 8;
    }
    *Rmask = *Gmask = *Bmask = *Amask = 0;

    if (format == SDL_PIXELFORMAT_RGB24) {
#if SDL_BYTEORDER == SDL_BIG_ENDIAN
        *Rmask = 0x00FF0000;
        *Gmask = 0x0000FF00;
        *Bmask = 0x000000FF;
#else
        *Rmask = 0x000000FF;
        *Gmask = 0x0000FF00;
        *Bmask = 0x00FF0000;
#endif
        return SDL_TRUE;
    }

    if (format == SDL_PIXELFORMAT_BGR24) {
#if SDL_BYTEORDER == SDL_BIG_ENDIAN
        *Rmask = 0x000000FF;
        *Gmask = 0x0000FF00;
        *Bmask = 0x00FF0000;
#else
        *Rmask = 0x00FF0000;
        *Gmask = 0x0000FF00;
        *Bmask = 0x000000FF;
#endif
        return SDL_TRUE;
    }

    if (SDL_PIXELTYPE(format) != SDL_PIXELTYPE_PACKED8 &&
        SDL_PIXELTYPE(format) != SDL_PIXELTYPE_PACKED16 &&
        SDL_PIXELTYPE(format) != SDL_PIXELTYPE_PACKED32) {
        /* Not a format that uses masks */
        return SDL_TRUE;
    }

    switch (SDL_PIXELLAYOUT(format)) {
    case SDL_PACKEDLAYOUT_332:
        masks[0] = 0x00000000;
        masks[1] = 0x000000E0;
        masks[2] = 0x0000001C;
        masks[3] = 0x00000003;
        break;
    case SDL_PACKEDLAYOUT_4444:
        masks[0] = 0x0000F000;
        masks[1] = 0x00000F00;
        masks[2] = 0x000000F0;
        masks[3] = 0x0000000F;
        break;
    case SDL_PACKEDLAYOUT_1555:
        masks[0] = 0x00008000;
        masks[1] = 0x00007C00;
        masks[2] = 0x000003E0;
        masks[3] = 0x0000001F;
        break;
    case SDL_PACKEDLAYOUT_5551:
        masks[0] = 0x0000F800;
        masks[1] = 0x000007C0;
        masks[2] = 0x0000003E;
        masks[3] = 0x00000001;
        break;
    case SDL_PACKEDLAYOUT_565:
        masks[0] = 0x00000000;
        masks[1] = 0x0000F800;
        masks[2] = 0x000007E0;
        masks[3] = 0x0000001F;
        break;
    case SDL_PACKEDLAYOUT_8888:
        masks[0] = 0xFF000000;
        masks[1] = 0x00FF0000;
        masks[2] = 0x0000FF00;
        masks[3] = 0x000000FF;
        break;
    case SDL_PACKEDLAYOUT_2101010:
        masks[0] = 0xC0000000;
        masks[1] = 0x3FF00000;
        masks[2] = 0x000FFC00;
        masks[3] = 0x000003FF;
        break;
    case SDL_PACKEDLAYOUT_1010102:
        masks[0] = 0xFFC00000;
        masks[1] = 0x003FF000;
        masks[2] = 0x00000FFC;
        masks[3] = 0x00000003;
        break;
    default:
        SDL_SetError("Unknown pixel format");
        return SDL_FALSE;
    }

    switch (SDL_PIXELORDER(format)) {
    case SDL_PACKEDORDER_XRGB:
        *Rmask = masks[1];
        *Gmask = masks[2];
        *Bmask = masks[3];
        break;
    case SDL_PACKEDORDER_RGBX:
        *Rmask = masks[0];
        *Gmask = masks[1];
        *Bmask = masks[2];
        break;
    case SDL_PACKEDORDER_ARGB:
        *Amask = masks[0];
        *Rmask = masks[1];
        *Gmask = masks[2];
        *Bmask = masks[3];
        break;
    case SDL_PACKEDORDER_RGBA:
        *Rmask = masks[0];
        *Gmask = masks[1];
        *Bmask = masks[2];
        *Amask = masks[3];
        break;
    case SDL_PACKEDORDER_XBGR:
        *Bmask = masks[1];
        *Gmask = masks[2];
        *Rmask = masks[3];
        break;
    case SDL_PACKEDORDER_BGRX:
        *Bmask = masks[0];
        *Gmask = masks[1];
        *Rmask = masks[2];
        break;
    case SDL_PACKEDORDER_BGRA:
        *Bmask = masks[0];
        *Gmask = masks[1];
        *Rmask = masks[2];
        *Amask = masks[3];
        break;
    case SDL_PACKEDORDER_ABGR:
        *Amask = masks[0];
        *Bmask = masks[1];
        *Gmask = masks[2];
        *Rmask = masks[3];
        break;
    default:
        SDL_SetError("Unknown pixel format");
        return SDL_FALSE;
    }
    return SDL_TRUE;
}

Uint32
SDL_MasksToPixelFormatEnum(int bpp, Uint32 Rmask, Uint32 Gmask, Uint32 Bmask,
                           Uint32 Amask)
{
    switch (bpp) {
    case 1:
        /* SDL defaults to MSB ordering */
        return SDL_PIXELFORMAT_INDEX1MSB;
    case 4:
        /* SDL defaults to MSB ordering */
        return SDL_PIXELFORMAT_INDEX4MSB;
    case 8:
        if (Rmask == 0) {
            return SDL_PIXELFORMAT_INDEX8;
        }
        if (Rmask == 0xE0 &&
            Gmask == 0x1C &&
            Bmask == 0x03 &&
            Amask == 0x00) {
            return SDL_PIXELFORMAT_RGB332;
        }
        break;
    case 12:
        if (Rmask == 0) {
            return SDL_PIXELFORMAT_RGB444;
        }
        if (Rmask == 0x0F00 &&
            Gmask == 0x00F0 &&
            Bmask == 0x000F &&
            Amask == 0x0000) {
            return SDL_PIXELFORMAT_RGB444;
        }
        break;
    case 15:
        if (Rmask == 0) {
            return SDL_PIXELFORMAT_RGB555;
        }
        /* Fall through to 16-bit checks */
    case 16:
        if (Rmask == 0) {
            return SDL_PIXELFORMAT_RGB565;
        }
        if (Rmask == 0x7C00 &&
            Gmask == 0x03E0 &&
            Bmask == 0x001F &&
            Amask == 0x0000) {
            return SDL_PIXELFORMAT_RGB555;
        }
        if (Rmask == 0x001F &&
            Gmask == 0x03E0 &&
            Bmask == 0x7C00 &&
            Amask == 0x0000) {
            return SDL_PIXELFORMAT_BGR555;
        }
        if (Rmask == 0x0F00 &&
            Gmask == 0x00F0 &&
            Bmask == 0x000F &&
            Amask == 0xF000) {
            return SDL_PIXELFORMAT_ARGB4444;
        }
        if (Rmask == 0xF000 &&
            Gmask == 0x0F00 &&
            Bmask == 0x00F0 &&
            Amask == 0x000F) {
            return SDL_PIXELFORMAT_RGBA4444;
        }
        if (Rmask == 0x000F &&
            Gmask == 0x00F0 &&
            Bmask == 0x0F00 &&
            Amask == 0xF000) {
            return SDL_PIXELFORMAT_ABGR4444;
        }
        if (Rmask == 0x00F0 &&
            Gmask == 0x0F00 &&
            Bmask == 0xF000 &&
            Amask == 0x000F) {
            return SDL_PIXELFORMAT_BGRA4444;
        }
        if (Rmask == 0x7C00 &&
            Gmask == 0x03E0 &&
            Bmask == 0x001F &&
            Amask == 0x8000) {
            return SDL_PIXELFORMAT_ARGB1555;
        }
        if (Rmask == 0xF800 &&
            Gmask == 0x07C0 &&
            Bmask == 0x003E &&
            Amask == 0x0001) {
            return SDL_PIXELFORMAT_RGBA5551;
        }
        if (Rmask == 0x001F &&
            Gmask == 0x03E0 &&
            Bmask == 0x7C00 &&
            Amask == 0x8000) {
            return SDL_PIXELFORMAT_ABGR1555;
        }
        if (Rmask == 0x003E &&
            Gmask == 0x07C0 &&
            Bmask == 0xF800 &&
            Amask == 0x0001) {
            return SDL_PIXELFORMAT_BGRA5551;
        }
        if (Rmask == 0xF800 &&
            Gmask == 0x07E0 &&
            Bmask == 0x001F &&
            Amask == 0x0000) {
            return SDL_PIXELFORMAT_RGB565;
        }
        if (Rmask == 0x001F &&
            Gmask == 0x07E0 &&
            Bmask == 0xF800 &&
            Amask == 0x0000) {
            return SDL_PIXELFORMAT_BGR565;
        }
        break;
    case 24:
        switch (Rmask) {
        case 0:
        case 0x00FF0000:
#if SDL_BYTEORDER == SDL_BIG_ENDIAN
            return SDL_PIXELFORMAT_RGB24;
#else
            return SDL_PIXELFORMAT_BGR24;
#endif
        case 0x000000FF:
#if SDL_BYTEORDER == SDL_BIG_ENDIAN
            return SDL_PIXELFORMAT_BGR24;
#else
            return SDL_PIXELFORMAT_RGB24;
#endif
        }
    case 32:
        if (Rmask == 0) {
            return SDL_PIXELFORMAT_RGB888;
        }
        if (Rmask == 0x00FF0000 &&
            Gmask == 0x0000FF00 &&
            Bmask == 0x000000FF &&
            Amask == 0x00000000) {
            return SDL_PIXELFORMAT_RGB888;
        }
        if (Rmask == 0x000000FF &&
            Gmask == 0x0000FF00 &&
            Bmask == 0x00FF0000 &&
            Amask == 0x00000000) {
            return SDL_PIXELFORMAT_BGR888;
        }
        if (Rmask == 0x00FF0000 &&
            Gmask == 0x0000FF00 &&
            Bmask == 0x000000FF &&
            Amask == 0xFF000000) {
            return SDL_PIXELFORMAT_ARGB8888;
        }
        if (Rmask == 0xFF000000 &&
            Gmask == 0x00FF0000 &&
            Bmask == 0x0000FF00 &&
            Amask == 0x000000FF) {
            return SDL_PIXELFORMAT_RGBA8888;
        }
        if (Rmask == 0x000000FF &&
            Gmask == 0x0000FF00 &&
            Bmask == 0x00FF0000 &&
            Amask == 0xFF000000) {
            return SDL_PIXELFORMAT_ABGR8888;
        }
        if (Rmask == 0x0000FF00 &&
            Gmask == 0x00FF0000 &&
            Bmask == 0xFF000000 &&
            Amask == 0x000000FF) {
            return SDL_PIXELFORMAT_BGRA8888;
        }
        if (Rmask == 0x3FF00000 &&
            Gmask == 0x000FFC00 &&
            Bmask == 0x000003FF &&
            Amask == 0xC0000000) {
            return SDL_PIXELFORMAT_ARGB2101010;
        }
    }
    return SDL_PIXELFORMAT_UNKNOWN;
}

static SDL_PixelFormat *formats;

SDL_PixelFormat *
SDL_AllocFormat(Uint32 pixel_format)
{
    SDL_PixelFormat *format;

    /* Look it up in our list of previously allocated formats */
    for (format = formats; format; format = format->next) {
        if (pixel_format == format->format) {
            ++format->refcount;
            return format;
        }
    }

    /* Allocate an empty pixel format structure, and initialize it */
    format = SDL_malloc(sizeof(*format));
    if (format == NULL) {
        SDL_OutOfMemory();
        return NULL;
    }
    if (SDL_InitFormat(format, pixel_format) < 0) {
        SDL_free(format);
        return NULL;
    }

    if (!SDL_ISPIXELFORMAT_INDEXED(pixel_format)) {
        /* Cache the RGB formats */
        format->next = formats;
        formats = format;
    }
    return format;
}

int
SDL_InitFormat(SDL_PixelFormat * format, Uint32 pixel_format)
{
    int bpp;
    Uint32 Rmask, Gmask, Bmask, Amask;
    Uint32 mask;

    if (!SDL_PixelFormatEnumToMasks(pixel_format, &bpp,
                                    &Rmask, &Gmask, &Bmask, &Amask)) {
        return -1;
    }

    /* Set up the format */
    SDL_zerop(format);
    format->format = pixel_format;
    format->BitsPerPixel = bpp;
    format->BytesPerPixel = (bpp + 7) / 8;

    format->Rmask = Rmask;
    format->Rshift = 0;
    format->Rloss = 8;
    if (Rmask) {
        for (mask = Rmask; !(mask & 0x01); mask >>= 1)
            ++format->Rshift;
        for (; (mask & 0x01); mask >>= 1)
            --format->Rloss;
    }

    format->Gmask = Gmask;
    format->Gshift = 0;
    format->Gloss = 8;
    if (Gmask) {
        for (mask = Gmask; !(mask & 0x01); mask >>= 1)
            ++format->Gshift;
        for (; (mask & 0x01); mask >>= 1)
            --format->Gloss;
    }

    format->Bmask = Bmask;
    format->Bshift = 0;
    format->Bloss = 8;
    if (Bmask) {
        for (mask = Bmask; !(mask & 0x01); mask >>= 1)
            ++format->Bshift;
        for (; (mask & 0x01); mask >>= 1)
            --format->Bloss;
    }

    format->Amask = Amask;
    format->Ashift = 0;
    format->Aloss = 8;
    if (Amask) {
        for (mask = Amask; !(mask & 0x01); mask >>= 1)
            ++format->Ashift;
        for (; (mask & 0x01); mask >>= 1)
            --format->Aloss;
    }

    format->palette = NULL;
    format->refcount = 1;
    format->next = NULL;

    return 0;
}

void
SDL_FreeFormat(SDL_PixelFormat *format)
{
    SDL_PixelFormat *prev;

    if (!format) {
        return;
    }
    if (--format->refcount > 0) {
        return;
    }

    /* Remove this format from our list */
    if (format == formats) {
        formats = format->next;
    } else if (formats) {
        for (prev = formats; prev->next; prev = prev->next) {
            if (prev->next == format) {
                prev->next = format->next;
                break;
            }
        }
    }

    if (format->palette) {
        SDL_FreePalette(format->palette);
    }
    SDL_free(format);
}

SDL_Palette *
SDL_AllocPalette(int ncolors)
{
    SDL_Palette *palette;

    palette = (SDL_Palette *) SDL_malloc(sizeof(*palette));
    if (!palette) {
        SDL_OutOfMemory();
        return NULL;
    }
    palette->colors =
        (SDL_Color *) SDL_malloc(ncolors * sizeof(*palette->colors));
    if (!palette->colors) {
        SDL_free(palette);
        return NULL;
    }
    palette->ncolors = ncolors;
    palette->version = 1;
    palette->refcount = 1;

    SDL_memset(palette->colors, 0xFF, ncolors * sizeof(*palette->colors));

    return palette;
}

int
SDL_SetPixelFormatPalette(SDL_PixelFormat * format, SDL_Palette *palette)
{
    if (!format) {
        SDL_SetError("SDL_SetPixelFormatPalette() passed NULL format");
        return -1;
    }

    if (palette && palette->ncolors != (1 << format->BitsPerPixel)) {
        SDL_SetError("SDL_SetPixelFormatPalette() passed a palette that doesn't match the format");
        return -1;
    }

    if (format->palette == palette) {
        return 0;
    }

    if (format->palette) {
        SDL_FreePalette(format->palette);
    }

    format->palette = palette;

    if (format->palette) {
        ++format->palette->refcount;
    }

    return 0;
}

int
SDL_SetPaletteColors(SDL_Palette * palette, const SDL_Color * colors,
                     int firstcolor, int ncolors)
{
    int status = 0;

    /* Verify the parameters */
    if (!palette) {
        return -1;
    }
    if (ncolors > (palette->ncolors - firstcolor)) {
        ncolors = (palette->ncolors - firstcolor);
        status = -1;
    }

    if (colors != (palette->colors + firstcolor)) {
        SDL_memcpy(palette->colors + firstcolor, colors,
                   ncolors * sizeof(*colors));
    }
    ++palette->version;
    if (!palette->version) {
        palette->version = 1;
    }

    return status;
}

void
SDL_FreePalette(SDL_Palette * palette)
{
    if (!palette) {
        return;
    }
    if (--palette->refcount > 0) {
        return;
    }
    if (palette->colors) {
        SDL_free(palette->colors);
    }
    SDL_free(palette);
}

/*
 * Calculate an 8-bit (3 red, 3 green, 2 blue) dithered palette of colors
 */
void
SDL_DitherColors(SDL_Color * colors, int bpp)
{
    int i;
    if (bpp != 8)
        return;                 /* only 8bpp supported right now */

    for (i = 0; i < 256; i++) {
        int r, g, b;
        /* map each bit field to the full [0, 255] interval,
           so 0 is mapped to (0, 0, 0) and 255 to (255, 255, 255) */
        r = i & 0xe0;
        r |= r >> 3 | r >> 6;
        colors[i].r = r;
        g = (i << 3) & 0xe0;
        g |= g >> 3 | g >> 6;
        colors[i].g = g;
        b = i & 0x3;
        b |= b << 2;
        b |= b << 4;
        colors[i].b = b;
        colors[i].unused = SDL_ALPHA_OPAQUE;
    }
}

/* 
 * Calculate the pad-aligned scanline width of a surface
 */
int
SDL_CalculatePitch(SDL_Surface * surface)
{
    int pitch;

    /* Surface should be 4-byte aligned for speed */
    pitch = surface->w * surface->format->BytesPerPixel;
    switch (surface->format->BitsPerPixel) {
    case 1:
        pitch = (pitch + 7) / 8;
        break;
    case 4:
        pitch = (pitch + 1) / 2;
        break;
    default:
        break;
    }
    pitch = (pitch + 3) & ~3;   /* 4-byte aligning */
    return (pitch);
}

/*
 * Match an RGB value to a particular palette index
 */
Uint8
SDL_FindColor(SDL_Palette * pal, Uint8 r, Uint8 g, Uint8 b)
{
    /* Do colorspace distance matching */
    unsigned int smallest;
    unsigned int distance;
    int rd, gd, bd;
    int i;
    Uint8 pixel = 0;

    smallest = ~0;
    for (i = 0; i < pal->ncolors; ++i) {
        rd = pal->colors[i].r - r;
        gd = pal->colors[i].g - g;
        bd = pal->colors[i].b - b;
        distance = (rd * rd) + (gd * gd) + (bd * bd);
        if (distance < smallest) {
            pixel = i;
            if (distance == 0) {        /* Perfect match! */
                break;
            }
            smallest = distance;
        }
    }
    return (pixel);
}

/* Find the opaque pixel value corresponding to an RGB triple */
Uint32
SDL_MapRGB(const SDL_PixelFormat * format, Uint8 r, Uint8 g, Uint8 b)
{
    if (format->palette == NULL) {
        return (r >> format->Rloss) << format->Rshift
            | (g >> format->Gloss) << format->Gshift
            | (b >> format->Bloss) << format->Bshift | format->Amask;
    } else {
        return SDL_FindColor(format->palette, r, g, b);
    }
}

/* Find the pixel value corresponding to an RGBA quadruple */
Uint32
SDL_MapRGBA(const SDL_PixelFormat * format, Uint8 r, Uint8 g, Uint8 b,
            Uint8 a)
{
    if (format->palette == NULL) {
        return (r >> format->Rloss) << format->Rshift
            | (g >> format->Gloss) << format->Gshift
            | (b >> format->Bloss) << format->Bshift
            | ((a >> format->Aloss) << format->Ashift & format->Amask);
    } else {
        return SDL_FindColor(format->palette, r, g, b);
    }
}

void
SDL_GetRGB(Uint32 pixel, const SDL_PixelFormat * format, Uint8 * r, Uint8 * g,
           Uint8 * b)
{
    if (format->palette == NULL) {
        /*
         * This makes sure that the result is mapped to the
         * interval [0..255], and the maximum value for each
         * component is 255. This is important to make sure
         * that white is indeed reported as (255, 255, 255).
         * This only works for RGB bit fields at least 4 bit
         * wide, which is almost always the case.
         */
        unsigned v;
        v = (pixel & format->Rmask) >> format->Rshift;
        *r = (v << format->Rloss) + (v >> (8 - (format->Rloss << 1)));
        v = (pixel & format->Gmask) >> format->Gshift;
        *g = (v << format->Gloss) + (v >> (8 - (format->Gloss << 1)));
        v = (pixel & format->Bmask) >> format->Bshift;
        *b = (v << format->Bloss) + (v >> (8 - (format->Bloss << 1)));
    } else {
        if (pixel < format->palette->ncolors) {
            *r = format->palette->colors[pixel].r;
            *g = format->palette->colors[pixel].g;
            *b = format->palette->colors[pixel].b;
        } else {
            *r = *g = *b = 0;
        }
    }
}

void
SDL_GetRGBA(Uint32 pixel, const SDL_PixelFormat * format,
            Uint8 * r, Uint8 * g, Uint8 * b, Uint8 * a)
{
    if (format->palette == NULL) {
        /*
         * This makes sure that the result is mapped to the
         * interval [0..255], and the maximum value for each
         * component is 255. This is important to make sure
         * that white is indeed reported as (255, 255, 255),
         * and that opaque alpha is 255.
         * This only works for RGB bit fields at least 4 bit
         * wide, which is almost always the case.
         */
        unsigned v;
        v = (pixel & format->Rmask) >> format->Rshift;
        *r = (v << format->Rloss) + (v >> (8 - (format->Rloss << 1)));
        v = (pixel & format->Gmask) >> format->Gshift;
        *g = (v << format->Gloss) + (v >> (8 - (format->Gloss << 1)));
        v = (pixel & format->Bmask) >> format->Bshift;
        *b = (v << format->Bloss) + (v >> (8 - (format->Bloss << 1)));
        if (format->Amask) {
            v = (pixel & format->Amask) >> format->Ashift;
            *a = (v << format->Aloss) + (v >> (8 - (format->Aloss << 1)));
        } else {
            *a = SDL_ALPHA_OPAQUE;
        }
    } else {
        if (pixel < format->palette->ncolors) {
            *r = format->palette->colors[pixel].r;
            *g = format->palette->colors[pixel].g;
            *b = format->palette->colors[pixel].b;
            *a = SDL_ALPHA_OPAQUE;
        } else {
            *r = *g = *b = *a = 0;
        }
    }
}

/* Map from Palette to Palette */
static Uint8 *
Map1to1(SDL_Palette * src, SDL_Palette * dst, int *identical)
{
    Uint8 *map;
    int i;

    if (identical) {
        if (src->ncolors <= dst->ncolors) {
            /* If an identical palette, no need to map */
            if (src == dst
                ||
                (SDL_memcmp
                 (src->colors, dst->colors,
                  src->ncolors * sizeof(SDL_Color)) == 0)) {
                *identical = 1;
                return (NULL);
            }
        }
        *identical = 0;
    }
    map = (Uint8 *) SDL_malloc(src->ncolors);
    if (map == NULL) {
        SDL_OutOfMemory();
        return (NULL);
    }
    for (i = 0; i < src->ncolors; ++i) {
        map[i] = SDL_FindColor(dst,
                               src->colors[i].r, src->colors[i].g,
                               src->colors[i].b);
    }
    return (map);
}

/* Map from Palette to BitField */
static Uint8 *
Map1toN(SDL_PixelFormat * src, Uint8 Rmod, Uint8 Gmod, Uint8 Bmod, Uint8 Amod,
        SDL_PixelFormat * dst)
{
    Uint8 *map;
    int i;
    int bpp;
    SDL_Palette *pal = src->palette;

    bpp = ((dst->BytesPerPixel == 3) ? 4 : dst->BytesPerPixel);
    map = (Uint8 *) SDL_malloc(pal->ncolors * bpp);
    if (map == NULL) {
        SDL_OutOfMemory();
        return (NULL);
    }

    /* We memory copy to the pixel map so the endianness is preserved */
    for (i = 0; i < pal->ncolors; ++i) {
        Uint8 A = Amod;
        Uint8 R = (Uint8) ((pal->colors[i].r * Rmod) / 255);
        Uint8 G = (Uint8) ((pal->colors[i].g * Gmod) / 255);
        Uint8 B = (Uint8) ((pal->colors[i].b * Bmod) / 255);
        ASSEMBLE_RGBA(&map[i * bpp], dst->BytesPerPixel, dst, R, G, B, A);
    }
    return (map);
}

/* Map from BitField to Dithered-Palette to Palette */
static Uint8 *
MapNto1(SDL_PixelFormat * src, SDL_PixelFormat * dst, int *identical)
{
    /* Generate a 256 color dither palette */
    SDL_Palette dithered;
    SDL_Color colors[256];
    SDL_Palette *pal = dst->palette;

    dithered.ncolors = 256;
    SDL_DitherColors(colors, 8);
    dithered.colors = colors;
    return (Map1to1(&dithered, pal, identical));
}

SDL_BlitMap *
SDL_AllocBlitMap(void)
{
    SDL_BlitMap *map;

    /* Allocate the empty map */
    map = (SDL_BlitMap *) SDL_calloc(1, sizeof(*map));
    if (map == NULL) {
        SDL_OutOfMemory();
        return (NULL);
    }
    map->info.r = 0xFF;
    map->info.g = 0xFF;
    map->info.b = 0xFF;
    map->info.a = 0xFF;

    /* It's ready to go */
    return (map);
}

void
SDL_InvalidateMap(SDL_BlitMap * map)
{
    if (!map) {
        return;
    }
    map->dst = NULL;
    map->palette_version = 0;
    if (map->info.table) {
        SDL_free(map->info.table);
        map->info.table = NULL;
    }
}

int
SDL_MapSurface(SDL_Surface * src, SDL_Surface * dst)
{
    SDL_PixelFormat *srcfmt;
    SDL_PixelFormat *dstfmt;
    SDL_BlitMap *map;

    /* Clear out any previous mapping */
    map = src->map;
    if ((src->flags & SDL_RLEACCEL) == SDL_RLEACCEL) {
        SDL_UnRLESurface(src, 1);
    }
    SDL_InvalidateMap(map);

    /* Figure out what kind of mapping we're doing */
    map->identity = 0;
    srcfmt = src->format;
    dstfmt = dst->format;
    if (SDL_ISPIXELFORMAT_INDEXED(srcfmt->format)) {
        if (SDL_ISPIXELFORMAT_INDEXED(dstfmt->format)) {
            /* Palette --> Palette */
            map->info.table =
                Map1to1(srcfmt->palette, dstfmt->palette, &map->identity);
            if (!map->identity) {
                if (map->info.table == NULL) {
                    return (-1);
                }
            }
            if (srcfmt->BitsPerPixel != dstfmt->BitsPerPixel)
                map->identity = 0;
        } else {
            /* Palette --> BitField */
            map->info.table =
                Map1toN(srcfmt, src->map->info.r, src->map->info.g,
                        src->map->info.b, src->map->info.a, dstfmt);
            if (map->info.table == NULL) {
                return (-1);
            }
        }
    } else {
        if (SDL_ISPIXELFORMAT_INDEXED(dstfmt->format)) {
            /* BitField --> Palette */
            map->info.table = MapNto1(srcfmt, dstfmt, &map->identity);
            if (!map->identity) {
                if (map->info.table == NULL) {
                    return (-1);
                }
            }
            map->identity = 0;  /* Don't optimize to copy */
        } else {
            /* BitField --> BitField */
            if (srcfmt == dstfmt) {
                map->identity = 1;
            }
        }
    }

    map->dst = dst;

    if (dstfmt->palette) {
        map->palette_version = dstfmt->palette->version;
    } else {
        map->palette_version = 0;
    }

    /* Choose your blitters wisely */
    return (SDL_CalculateBlit(src));
}

void
SDL_FreeBlitMap(SDL_BlitMap * map)
{
    if (map) {
        SDL_InvalidateMap(map);
        SDL_free(map);
    }
}

/* vi: set ts=4 sw=4 expandtab: */