SDL_bmp.c File Reference

#include "../SDL_internal.h"
#include "SDL_hints.h"
#include "SDL_video.h"
#include "SDL_endian.h"
#include "SDL_pixels_c.h"

Include dependency graph for SDL_bmp.c:

Go to the source code of this file.

Macros
#define	SAVE_32BIT_BMP
#define	BI_RGB   0
#define	BI_RLE8   1
#define	BI_RLE4   2
#define	BI_BITFIELDS   3
#define	LCS_WINDOWS_COLOR_SPACE   0x57696E20
#define	COPY_PIXEL(x)   spot = &bits[ofs++]; if(spot >= start && spot < end) *spot = (x)

Functions
static int	readRlePixels (SDL_Surface *surface, SDL_RWops *src, int isRle8)
static void	CorrectAlphaChannel (SDL_Surface *surface)
SDL_Surface *	SDL_LoadBMP_RW (SDL_RWops *src, int freesrc)
int	SDL_SaveBMP_RW (SDL_Surface *saveme, SDL_RWops *dst, int freedst)

Macro Definition Documentation

BI_BITFIELDS

#define BI_BITFIELDS   3

Definition at line 47 of file SDL_bmp.c.

BI_RGB

#define BI_RGB   0

Definition at line 44 of file SDL_bmp.c.

BI_RLE4

#define BI_RLE4   2

Definition at line 46 of file SDL_bmp.c.

BI_RLE8

#define BI_RLE8   1

Definition at line 45 of file SDL_bmp.c.

COPY_PIXEL

#define COPY_PIXEL

(

x

)

spot = &bits[ofs++]; if(spot >= start && spot < end) *spot = (x)

LCS_WINDOWS_COLOR_SPACE

#define LCS_WINDOWS_COLOR_SPACE   0x57696E20

Definition at line 53 of file SDL_bmp.c.

SAVE_32BIT_BMP

#define SAVE_32BIT_BMP

Definition at line 40 of file SDL_bmp.c.

Function Documentation

CorrectAlphaChannel()

static void CorrectAlphaChannel ( SDL_Surface *  surface )

static

Definition at line 142 of file SDL_bmp.c.

{
    /* Check to see if there is any alpha channel data */
    SDL_bool hasAlpha = SDL_FALSE;
#if SDL_BYTEORDER == SDL_BIG_ENDIAN
    int alphaChannelOffset = 0;
#else
    int alphaChannelOffset = 3;
#endif
    Uint8 *alpha = ((Uint8*)surface->pixels) + alphaChannelOffset;
    Uint8 *end = alpha + surface->h * surface->pitch;
 
    while (alpha < end) {
        if (*alpha != 0) {
            hasAlpha = SDL_TRUE;
            break;
        }
        alpha += 4;
    }
 
    if (!hasAlpha) {
        alpha = ((Uint8*)surface->pixels) + alphaChannelOffset;
        while (alpha < end) {
            *alpha = SDL_ALPHA_OPAQUE;
            alpha += 4;
        }
    }
}

References SDL_ALPHA_OPAQUE, SDL_FALSE, and SDL_TRUE.

Referenced by SDL_LoadBMP_RW().

readRlePixels()

static int readRlePixels ( SDL_Surface *  surface, SDL_RWops *  src, int  isRle8  )

static

Definition at line 56 of file SDL_bmp.c.

{
    /*
    | Sets the surface pixels from src.  A bmp image is upside down.
    */
    int pitch = surface->pitch;
    int height = surface->h;
    Uint8 *start = (Uint8 *)surface->pixels;
    Uint8 *end = start + (height*pitch);
    Uint8 *bits = end-pitch, *spot;
    int ofs = 0;
    Uint8 ch;
    Uint8 needsPad;
 
#define COPY_PIXEL(x)   spot = &bits[ofs++]; if(spot >= start && spot < end) *spot = (x)
 
    for (;;) {
        if (!SDL_RWread(src, &ch, 1, 1)) return 1;
        /*
        | encoded mode starts with a run length, and then a byte
        | with two colour indexes to alternate between for the run
        */
        if (ch) {
            Uint8 pixel;
            if (!SDL_RWread(src, &pixel, 1, 1)) return 1;
            if (isRle8) {                   /* 256-color bitmap, compressed */
                do {
                    COPY_PIXEL(pixel);
                } while (--ch);
            } else {                         /* 16-color bitmap, compressed */
                Uint8 pixel0 = pixel >> 4;
                Uint8 pixel1 = pixel & 0x0F;
                for (;;) {
                    COPY_PIXEL(pixel0); /* even count, high nibble */
                    if (!--ch) break;
                    COPY_PIXEL(pixel1); /* odd count, low nibble */
                    if (!--ch) break;
                }
            }
        } else {
            /*
            | A leading zero is an escape; it may signal the end of the bitmap,
            | a cursor move, or some absolute data.
            | zero tag may be absolute mode or an escape
            */
            if (!SDL_RWread(src, &ch, 1, 1)) return 1;
            switch (ch) {
            case 0:                         /* end of line */
                ofs = 0;
                bits -= pitch;               /* go to previous */
                break;
            case 1:                         /* end of bitmap */
                return 0;                    /* success! */
            case 2:                         /* delta */
                if (!SDL_RWread(src, &ch, 1, 1)) return 1;
                ofs += ch;
                if (!SDL_RWread(src, &ch, 1, 1)) return 1;
                bits -= (ch * pitch);
                break;
            default:                        /* no compression */
                if (isRle8) {
                    needsPad = (ch & 1);
                    do {
                        Uint8 pixel;
                        if (!SDL_RWread(src, &pixel, 1, 1)) return 1;
                        COPY_PIXEL(pixel);
                    } while (--ch);
                } else {
                    needsPad = (((ch+1)>>1) & 1); /* (ch+1)>>1: bytes size */
                    for (;;) {
                        Uint8 pixel;
                        if (!SDL_RWread(src, &pixel, 1, 1)) return 1;
                        COPY_PIXEL(pixel >> 4);
                        if (!--ch) break;
                        COPY_PIXEL(pixel & 0x0F);
                        if (!--ch) break;
                    }
                }
                /* pad at even boundary */
                if (needsPad && !SDL_RWread(src, &ch, 1, 1)) return 1;
                break;
            }
        }
    }
}

References COPY_PIXEL, and SDL_RWread.

Referenced by SDL_LoadBMP_RW().

SDL_LoadBMP_RW()

SDL_Surface* SDL_LoadBMP_RW	(	SDL_RWops *	src,
		int	freesrc
	)

Load a surface from a seekable SDL data stream (memory or file).

If freesrc is non-zero, the stream will be closed after being read.

The new surface should be freed with SDL_FreeSurface().

Returns

the new surface, or NULL if there was an error.

Definition at line 172 of file SDL_bmp.c.

{
    SDL_bool was_error;
    Sint64 fp_offset = 0;
    int bmpPitch;
    int i, pad;
    SDL_Surface *surface;
    Uint32 Rmask = 0;
    Uint32 Gmask = 0;
    Uint32 Bmask = 0;
    Uint32 Amask = 0;
    SDL_Palette *palette;
    Uint8 *bits;
    Uint8 *top, *end;
    SDL_bool topDown;
    int ExpandBMP;
    SDL_bool haveRGBMasks = SDL_FALSE;
    SDL_bool haveAlphaMask = SDL_FALSE;
    SDL_bool correctAlpha = SDL_FALSE;
 
    /* The Win32 BMP file header (14 bytes) */
    char magic[2];
    /* Uint32 bfSize; */
    /* Uint16 bfReserved1; */
    /* Uint16 bfReserved2; */
    Uint32 bfOffBits;
 
    /* The Win32 BITMAPINFOHEADER struct (40 bytes) */
    Uint32 biSize;
    Sint32 biWidth = 0;
    Sint32 biHeight = 0;
    /* Uint16 biPlanes; */
    Uint16 biBitCount = 0;
    Uint32 biCompression = 0;
    /* Uint32 biSizeImage; */
    /* Sint32 biXPelsPerMeter; */
    /* Sint32 biYPelsPerMeter; */
    Uint32 biClrUsed = 0;
    /* Uint32 biClrImportant; */
 
    /* Make sure we are passed a valid data source */
    surface = NULL;
    was_error = SDL_FALSE;
    if (src == NULL) {
        was_error = SDL_TRUE;
        goto done;
    }
 
    /* Read in the BMP file header */
    fp_offset = SDL_RWtell(src);
    SDL_ClearError();
    if (SDL_RWread(src, magic, 1, 2) != 2) {
        SDL_Error(SDL_EFREAD);
        was_error = SDL_TRUE;
        goto done;
    }
    if (SDL_strncmp(magic, "BM", 2) != 0) {
        SDL_SetError("File is not a Windows BMP file");
        was_error = SDL_TRUE;
        goto done;
    }
    /* bfSize      = */ SDL_ReadLE32(src);
    /* bfReserved1 = */ SDL_ReadLE16(src);
    /* bfReserved2 = */ SDL_ReadLE16(src);
    bfOffBits   = SDL_ReadLE32(src);
 
    /* Read the Win32 BITMAPINFOHEADER */
    biSize = SDL_ReadLE32(src);
    if (biSize == 12) {   /* really old BITMAPCOREHEADER */
        biWidth = (Uint32) SDL_ReadLE16(src);
        biHeight = (Uint32) SDL_ReadLE16(src);
        /* biPlanes = */ SDL_ReadLE16(src);
        biBitCount = SDL_ReadLE16(src);
        biCompression = BI_RGB;
        /* biSizeImage = 0; */
        /* biXPelsPerMeter = 0; */
        /* biYPelsPerMeter = 0; */
        biClrUsed = 0;
        /* biClrImportant = 0; */
    } else if (biSize >= 40) {  /* some version of BITMAPINFOHEADER */
        Uint32 headerSize;
        biWidth = SDL_ReadLE32(src);
        biHeight = SDL_ReadLE32(src);
        /* biPlanes = */ SDL_ReadLE16(src);
        biBitCount = SDL_ReadLE16(src);
        biCompression = SDL_ReadLE32(src);
        /* biSizeImage = */ SDL_ReadLE32(src);
        /* biXPelsPerMeter = */ SDL_ReadLE32(src);
        /* biYPelsPerMeter = */ SDL_ReadLE32(src);
        biClrUsed = SDL_ReadLE32(src);
        /* biClrImportant = */ SDL_ReadLE32(src);
 
        /* 64 == BITMAPCOREHEADER2, an incompatible OS/2 2.x extension. Skip this stuff for now. */
        if (biSize != 64) {
            /* This is complicated. If compression is BI_BITFIELDS, then
               we have 3 DWORDS that specify the RGB masks. This is either
               stored here in an BITMAPV2INFOHEADER (which only differs in
               that it adds these RGB masks) and biSize >= 52, or we've got
               these masks stored in the exact same place, but strictly
               speaking, this is the bmiColors field in BITMAPINFO immediately
               following the legacy v1 info header, just past biSize. */
            if (biCompression == BI_BITFIELDS) {
                haveRGBMasks = SDL_TRUE;
                Rmask = SDL_ReadLE32(src);
                Gmask = SDL_ReadLE32(src);
                Bmask = SDL_ReadLE32(src);
 
                /* ...v3 adds an alpha mask. */
                if (biSize >= 56) {  /* BITMAPV3INFOHEADER; adds alpha mask */
                    haveAlphaMask = SDL_TRUE;
                    Amask = SDL_ReadLE32(src);
                }
            } else {
                /* the mask fields are ignored for v2+ headers if not BI_BITFIELD. */
                if (biSize >= 52) {  /* BITMAPV2INFOHEADER; adds RGB masks */
                    /*Rmask = */ SDL_ReadLE32(src);
                    /*Gmask = */ SDL_ReadLE32(src);
                    /*Bmask = */ SDL_ReadLE32(src);
                }
                if (biSize >= 56) {  /* BITMAPV3INFOHEADER; adds alpha mask */
                    /*Amask = */ SDL_ReadLE32(src);
                }
            }
 
            /* Insert other fields here; Wikipedia and MSDN say we're up to
               v5 of this header, but we ignore those for now (they add gamma,
               color spaces, etc). Ignoring the weird OS/2 2.x format, we
               currently parse up to v3 correctly (hopefully!). */
        }
 
        /* skip any header bytes we didn't handle... */
        headerSize = (Uint32) (SDL_RWtell(src) - (fp_offset + 14));
        if (biSize > headerSize) {
            SDL_RWseek(src, (biSize - headerSize), RW_SEEK_CUR);
        }
    }
    if (biWidth <= 0 || biHeight == 0) {
        SDL_SetError("BMP file with bad dimensions (%dx%d)", biWidth, biHeight);
        was_error = SDL_TRUE;
        goto done;
    }
    if (biHeight < 0) {
        topDown = SDL_TRUE;
        biHeight = -biHeight;
    } else {
        topDown = SDL_FALSE;
    }
 
    /* Check for read error */
    if (SDL_strcmp(SDL_GetError(), "") != 0) {
        was_error = SDL_TRUE;
        goto done;
    }
 
    /* Expand 1 and 4 bit bitmaps to 8 bits per pixel */
    switch (biBitCount) {
    case 1:
    case 4:
        ExpandBMP = biBitCount;
        biBitCount = 8;
        break;
    case 0:
    case 2:
    case 3:
    case 5:
    case 6:
    case 7:
        SDL_SetError("%d-bpp BMP images are not supported", biBitCount);
        was_error = SDL_TRUE;
        goto done;
    default:
        ExpandBMP = 0;
        break;
    }
 
    /* RLE4 and RLE8 BMP compression is supported */
    switch (biCompression) {
    case BI_RGB:
        /* If there are no masks, use the defaults */
        SDL_assert(!haveRGBMasks);
        SDL_assert(!haveAlphaMask);
        /* Default values for the BMP format */
        switch (biBitCount) {
        case 15:
        case 16:
            Rmask = 0x7C00;
            Gmask = 0x03E0;
            Bmask = 0x001F;
            break;
        case 24:
#if SDL_BYTEORDER == SDL_BIG_ENDIAN
            Rmask = 0x000000FF;
            Gmask = 0x0000FF00;
            Bmask = 0x00FF0000;
#else
            Rmask = 0x00FF0000;
            Gmask = 0x0000FF00;
            Bmask = 0x000000FF;
#endif
            break;
        case 32:
            /* We don't know if this has alpha channel or not */
            correctAlpha = SDL_TRUE;
            Amask = 0xFF000000;
            Rmask = 0x00FF0000;
            Gmask = 0x0000FF00;
            Bmask = 0x000000FF;
            break;
        default:
            break;
        }
        break;
 
    case BI_BITFIELDS:
        break;  /* we handled this in the info header. */
 
    default:
        break;
    }
 
    /* Create a compatible surface, note that the colors are RGB ordered */
    surface =
        SDL_CreateRGBSurface(0, biWidth, biHeight, biBitCount, Rmask, Gmask,
                             Bmask, Amask);
    if (surface == NULL) {
        was_error = SDL_TRUE;
        goto done;
    }
 
    /* Load the palette, if any */
    palette = (surface->format)->palette;
    if (palette) {
        if (SDL_RWseek(src, fp_offset+14+biSize, RW_SEEK_SET) < 0) {
            SDL_Error(SDL_EFSEEK);
            was_error = SDL_TRUE;
            goto done;
        }
 
        /*
        | guich: always use 1<<bpp b/c some bitmaps can bring wrong information
        | for colorsUsed
        */
        /* if (biClrUsed == 0) {  */
        biClrUsed = 1 << biBitCount;
        /* } */
        if (biSize == 12) {
            for (i = 0; i < (int) biClrUsed; ++i) {
                SDL_RWread(src, &palette->colors[i].b, 1, 1);
                SDL_RWread(src, &palette->colors[i].g, 1, 1);
                SDL_RWread(src, &palette->colors[i].r, 1, 1);
                palette->colors[i].a = SDL_ALPHA_OPAQUE;
            }
        } else {
            for (i = 0; i < (int) biClrUsed; ++i) {
                SDL_RWread(src, &palette->colors[i].b, 1, 1);
                SDL_RWread(src, &palette->colors[i].g, 1, 1);
                SDL_RWread(src, &palette->colors[i].r, 1, 1);
                SDL_RWread(src, &palette->colors[i].a, 1, 1);
 
                /* According to Microsoft documentation, the fourth element
                   is reserved and must be zero, so we shouldn't treat it as
                   alpha.
                */
                palette->colors[i].a = SDL_ALPHA_OPAQUE;
            }
        }
        palette->ncolors = biClrUsed;
    }
 
    /* Read the surface pixels.  Note that the bmp image is upside down */
    if (SDL_RWseek(src, fp_offset + bfOffBits, RW_SEEK_SET) < 0) {
        SDL_Error(SDL_EFSEEK);
        was_error = SDL_TRUE;
        goto done;
    }
    if ((biCompression == BI_RLE4) || (biCompression == BI_RLE8)) {
        was_error = (SDL_bool)readRlePixels(surface, src, biCompression == BI_RLE8);
        if (was_error) SDL_SetError("Error reading from BMP");
        goto done;
    }
    top = (Uint8 *)surface->pixels;
    end = (Uint8 *)surface->pixels+(surface->h*surface->pitch);
    switch (ExpandBMP) {
    case 1:
        bmpPitch = (biWidth + 7) >> 3;
        pad = (((bmpPitch) % 4) ? (4 - ((bmpPitch) % 4)) : 0);
        break;
    case 4:
        bmpPitch = (biWidth + 1) >> 1;
        pad = (((bmpPitch) % 4) ? (4 - ((bmpPitch) % 4)) : 0);
        break;
    default:
        pad = ((surface->pitch % 4) ? (4 - (surface->pitch % 4)) : 0);
        break;
    }
    if (topDown) {
        bits = top;
    } else {
        bits = end - surface->pitch;
    }
    while (bits >= top && bits < end) {
        switch (ExpandBMP) {
        case 1:
        case 4:{
                Uint8 pixel = 0;
                int shift = (8 - ExpandBMP);
                for (i = 0; i < surface->w; ++i) {
                    if (i % (8 / ExpandBMP) == 0) {
                        if (!SDL_RWread(src, &pixel, 1, 1)) {
                            SDL_SetError("Error reading from BMP");
                            was_error = SDL_TRUE;
                            goto done;
                        }
                    }
                    bits[i] = (pixel >> shift);
                    if (bits[i] >= biClrUsed) {
                        SDL_SetError("A BMP image contains a pixel with a color out of the palette");
                        was_error = SDL_TRUE;
                        goto done;
                    }
                    pixel <<= ExpandBMP;
                }
            }
            break;
 
        default:
            if (SDL_RWread(src, bits, 1, surface->pitch) != surface->pitch) {
                SDL_Error(SDL_EFREAD);
                was_error = SDL_TRUE;
                goto done;
            }
            if (biBitCount == 8 && palette && biClrUsed < (1u << biBitCount)) {
                for (i = 0; i < surface->w; ++i) {
                    if (bits[i] >= biClrUsed) {
                        SDL_SetError("A BMP image contains a pixel with a color out of the palette");
                        was_error = SDL_TRUE;
                        goto done;
                    }
                }
            }
#if SDL_BYTEORDER == SDL_BIG_ENDIAN
            /* Byte-swap the pixels if needed. Note that the 24bpp
               case has already been taken care of above. */
            switch (biBitCount) {
            case 15:
            case 16:{
                    Uint16 *pix = (Uint16 *) bits;
                    for (i = 0; i < surface->w; i++)
                        pix[i] = SDL_Swap16(pix[i]);
                    break;
                }
 
            case 32:{
                    Uint32 *pix = (Uint32 *) bits;
                    for (i = 0; i < surface->w; i++)
                        pix[i] = SDL_Swap32(pix[i]);
                    break;
                }
            }
#endif
            break;
        }
        /* Skip padding bytes, ugh */
        if (pad) {
            Uint8 padbyte;
            for (i = 0; i < pad; ++i) {
                SDL_RWread(src, &padbyte, 1, 1);
            }
        }
        if (topDown) {
            bits += surface->pitch;
        } else {
            bits -= surface->pitch;
        }
    }
    if (correctAlpha) {
        CorrectAlphaChannel(surface);
    }
  done:
    if (was_error) {
        if (src) {
            SDL_RWseek(src, fp_offset, RW_SEEK_SET);
        }
        if (surface) {
            SDL_FreeSurface(surface);
        }
        surface = NULL;
    }
    if (freesrc && src) {
        SDL_RWclose(src);
    }
    return (surface);
}

References SDL_Color::a, SDL_Color::b, BI_BITFIELDS, BI_RGB, BI_RLE4, BI_RLE8, SDL_Palette::colors, CorrectAlphaChannel(), done, SDL_Color::g, i, int(), SDL_Palette::ncolors, NULL, SDL_Color::r, readRlePixels(), RW_SEEK_CUR, RW_SEEK_SET, SDL_ALPHA_OPAQUE, SDL_assert, SDL_ClearError, SDL_CreateRGBSurface, SDL_EFREAD, SDL_EFSEEK, SDL_Error, SDL_FALSE, SDL_FreeSurface, SDL_GetError, SDL_ReadLE16, SDL_ReadLE32, SDL_RWclose, SDL_RWread, SDL_RWseek, SDL_RWtell, SDL_SetError, SDL_strcmp, SDL_strncmp, SDL_Swap16(), SDL_Swap32(), and SDL_TRUE.

SDL_SaveBMP_RW()

int SDL_SaveBMP_RW	(	SDL_Surface *	surface,
		SDL_RWops *	dst,
		int	freedst
	)

Save a surface to a seekable SDL data stream (memory or file).

Surfaces with a 24-bit, 32-bit and paletted 8-bit format get saved in the BMP directly. Other RGB formats with 8-bit or higher get converted to a 24-bit surface or, if they have an alpha mask or a colorkey, to a 32-bit surface before they are saved. YUV and paletted 1-bit and 4-bit formats are not supported.

If freedst is non-zero, the stream will be closed after being written.

Returns

0 if successful or -1 if there was an error.

Definition at line 567 of file SDL_bmp.c.

{
    Sint64 fp_offset;
    int i, pad;
    SDL_Surface *surface;
    Uint8 *bits;
    SDL_bool save32bit = SDL_FALSE;
    SDL_bool saveLegacyBMP = SDL_FALSE;
 
    /* The Win32 BMP file header (14 bytes) */
    char magic[2] = { 'B', 'M' };
    Uint32 bfSize;
    Uint16 bfReserved1;
    Uint16 bfReserved2;
    Uint32 bfOffBits;
 
    /* The Win32 BITMAPINFOHEADER struct (40 bytes) */
    Uint32 biSize;
    Sint32 biWidth;
    Sint32 biHeight;
    Uint16 biPlanes;
    Uint16 biBitCount;
    Uint32 biCompression;
    Uint32 biSizeImage;
    Sint32 biXPelsPerMeter;
    Sint32 biYPelsPerMeter;
    Uint32 biClrUsed;
    Uint32 biClrImportant;
 
    /* The additional header members from the Win32 BITMAPV4HEADER struct (108 bytes in total) */
    Uint32 bV4RedMask = 0;
    Uint32 bV4GreenMask = 0;
    Uint32 bV4BlueMask = 0;
    Uint32 bV4AlphaMask = 0;
    Uint32 bV4CSType = 0;
    Sint32 bV4Endpoints[3 * 3] = {0};
    Uint32 bV4GammaRed = 0;
    Uint32 bV4GammaGreen = 0;
    Uint32 bV4GammaBlue = 0;
 
    /* Make sure we have somewhere to save */
    surface = NULL;
    if (dst) {
#ifdef SAVE_32BIT_BMP
        /* We can save alpha information in a 32-bit BMP */
        if (saveme->format->BitsPerPixel >= 8 && (saveme->format->Amask ||
            saveme->map->info.flags & SDL_COPY_COLORKEY)) {
            save32bit = SDL_TRUE;
        }
#endif /* SAVE_32BIT_BMP */
 
        if (saveme->format->palette && !save32bit) {
            if (saveme->format->BitsPerPixel == 8) {
                surface = saveme;
            } else {
                SDL_SetError("%d bpp BMP files not supported",
                             saveme->format->BitsPerPixel);
            }
        } else if ((saveme->format->BitsPerPixel == 24) && !save32bit &&
#if SDL_BYTEORDER == SDL_LIL_ENDIAN
                   (saveme->format->Rmask == 0x00FF0000) &&
                   (saveme->format->Gmask == 0x0000FF00) &&
                   (saveme->format->Bmask == 0x000000FF)
#else
                   (saveme->format->Rmask == 0x000000FF) &&
                   (saveme->format->Gmask == 0x0000FF00) &&
                   (saveme->format->Bmask == 0x00FF0000)
#endif
            ) {
            surface = saveme;
        } else {
            SDL_PixelFormat format;
 
            /* If the surface has a colorkey or alpha channel we'll save a
               32-bit BMP with alpha channel, otherwise save a 24-bit BMP. */
            if (save32bit) {
                SDL_InitFormat(&format, SDL_PIXELFORMAT_BGRA32);
            } else {
                SDL_InitFormat(&format, SDL_PIXELFORMAT_BGR24);
            }
            surface = SDL_ConvertSurface(saveme, &format, 0);
            if (!surface) {
                SDL_SetError("Couldn't convert image to %d bpp",
                             format.BitsPerPixel);
            }
        }
    } else {
        /* Set no error here because it may overwrite a more useful message from
           SDL_RWFromFile() if SDL_SaveBMP_RW() is called from SDL_SaveBMP(). */
        return -1;
    }
 
    if (save32bit) {
        saveLegacyBMP = SDL_GetHintBoolean(SDL_HINT_BMP_SAVE_LEGACY_FORMAT, SDL_FALSE);
    }
 
    if (surface && (SDL_LockSurface(surface) == 0)) {
        const int bw = surface->w * surface->format->BytesPerPixel;
 
        /* Set the BMP file header values */
        bfSize = 0;             /* We'll write this when we're done */
        bfReserved1 = 0;
        bfReserved2 = 0;
        bfOffBits = 0;          /* We'll write this when we're done */
 
        /* Write the BMP file header values */
        fp_offset = SDL_RWtell(dst);
        SDL_ClearError();
        SDL_RWwrite(dst, magic, 2, 1);
        SDL_WriteLE32(dst, bfSize);
        SDL_WriteLE16(dst, bfReserved1);
        SDL_WriteLE16(dst, bfReserved2);
        SDL_WriteLE32(dst, bfOffBits);
 
        /* Set the BMP info values */
        biSize = 40;
        biWidth = surface->w;
        biHeight = surface->h;
        biPlanes = 1;
        biBitCount = surface->format->BitsPerPixel;
        biCompression = BI_RGB;
        biSizeImage = surface->h * surface->pitch;
        biXPelsPerMeter = 0;
        biYPelsPerMeter = 0;
        if (surface->format->palette) {
            biClrUsed = surface->format->palette->ncolors;
        } else {
            biClrUsed = 0;
        }
        biClrImportant = 0;
 
        /* Set the BMP info values for the version 4 header */
        if (save32bit && !saveLegacyBMP) {
            biSize = 108;
            biCompression = BI_BITFIELDS;
            /* The BMP format is always little endian, these masks stay the same */
            bV4RedMask   = 0x00ff0000;
            bV4GreenMask = 0x0000ff00;
            bV4BlueMask  = 0x000000ff;
            bV4AlphaMask = 0xff000000;
            bV4CSType = LCS_WINDOWS_COLOR_SPACE;
            bV4GammaRed = 0;
            bV4GammaGreen = 0;
            bV4GammaBlue = 0;
        }
 
        /* Write the BMP info values */
        SDL_WriteLE32(dst, biSize);
        SDL_WriteLE32(dst, biWidth);
        SDL_WriteLE32(dst, biHeight);
        SDL_WriteLE16(dst, biPlanes);
        SDL_WriteLE16(dst, biBitCount);
        SDL_WriteLE32(dst, biCompression);
        SDL_WriteLE32(dst, biSizeImage);
        SDL_WriteLE32(dst, biXPelsPerMeter);
        SDL_WriteLE32(dst, biYPelsPerMeter);
        SDL_WriteLE32(dst, biClrUsed);
        SDL_WriteLE32(dst, biClrImportant);
 
        /* Write the BMP info values for the version 4 header */
        if (save32bit && !saveLegacyBMP) {
            SDL_WriteLE32(dst, bV4RedMask);
            SDL_WriteLE32(dst, bV4GreenMask);
            SDL_WriteLE32(dst, bV4BlueMask);
            SDL_WriteLE32(dst, bV4AlphaMask);
            SDL_WriteLE32(dst, bV4CSType);
            for (i = 0; i < 3 * 3; i++) {
                SDL_WriteLE32(dst, bV4Endpoints[i]);
            }
            SDL_WriteLE32(dst, bV4GammaRed);
            SDL_WriteLE32(dst, bV4GammaGreen);
            SDL_WriteLE32(dst, bV4GammaBlue);
        }
 
        /* Write the palette (in BGR color order) */
        if (surface->format->palette) {
            SDL_Color *colors;
            int ncolors;
 
            colors = surface->format->palette->colors;
            ncolors = surface->format->palette->ncolors;
            for (i = 0; i < ncolors; ++i) {
                SDL_RWwrite(dst, &colors[i].b, 1, 1);
                SDL_RWwrite(dst, &colors[i].g, 1, 1);
                SDL_RWwrite(dst, &colors[i].r, 1, 1);
                SDL_RWwrite(dst, &colors[i].a, 1, 1);
            }
        }
 
        /* Write the bitmap offset */
        bfOffBits = (Uint32)(SDL_RWtell(dst) - fp_offset);
        if (SDL_RWseek(dst, fp_offset + 10, RW_SEEK_SET) < 0) {
            SDL_Error(SDL_EFSEEK);
        }
        SDL_WriteLE32(dst, bfOffBits);
        if (SDL_RWseek(dst, fp_offset + bfOffBits, RW_SEEK_SET) < 0) {
            SDL_Error(SDL_EFSEEK);
        }
 
        /* Write the bitmap image upside down */
        bits = (Uint8 *) surface->pixels + (surface->h * surface->pitch);
        pad = ((bw % 4) ? (4 - (bw % 4)) : 0);
        while (bits > (Uint8 *) surface->pixels) {
            bits -= surface->pitch;
            if (SDL_RWwrite(dst, bits, 1, bw) != bw) {
                SDL_Error(SDL_EFWRITE);
                break;
            }
            if (pad) {
                const Uint8 padbyte = 0;
                for (i = 0; i < pad; ++i) {
                    SDL_RWwrite(dst, &padbyte, 1, 1);
                }
            }
        }
 
        /* Write the BMP file size */
        bfSize = (Uint32)(SDL_RWtell(dst) - fp_offset);
        if (SDL_RWseek(dst, fp_offset + 2, RW_SEEK_SET) < 0) {
            SDL_Error(SDL_EFSEEK);
        }
        SDL_WriteLE32(dst, bfSize);
        if (SDL_RWseek(dst, fp_offset + bfSize, RW_SEEK_SET) < 0) {
            SDL_Error(SDL_EFSEEK);
        }
 
        /* Close it up.. */
        SDL_UnlockSurface(surface);
        if (surface != saveme) {
            SDL_FreeSurface(surface);
        }
    }
 
    if (freedst && dst) {
        SDL_RWclose(dst);
    }
    return ((SDL_strcmp(SDL_GetError(), "") == 0) ? 0 : -1);
}

References SDL_PixelFormat::Amask, BI_BITFIELDS, BI_RGB, SDL_PixelFormat::BitsPerPixel, SDL_PixelFormat::Bmask, colors, endif, SDL_BlitInfo::flags, SDL_Surface::format, SDL_PixelFormat::Gmask, i, SDL_BlitMap::info, LCS_WINDOWS_COLOR_SPACE, SDL_Surface::map, NULL, SDL_PixelFormat::palette, SDL_PixelFormat::Rmask, RW_SEEK_SET, SDL_BYTEORDER, SDL_ClearError, SDL_ConvertSurface, SDL_COPY_COLORKEY, SDL_EFSEEK, SDL_EFWRITE, SDL_Error, SDL_FALSE, SDL_FreeSurface, SDL_GetError, SDL_GetHintBoolean, SDL_HINT_BMP_SAVE_LEGACY_FORMAT, SDL_InitFormat(), SDL_LIL_ENDIAN, SDL_LockSurface, SDL_PIXELFORMAT_BGR24, SDL_PIXELFORMAT_BGRA32, SDL_RWclose, SDL_RWseek, SDL_RWtell, SDL_RWwrite, SDL_SetError, SDL_strcmp, SDL_TRUE, SDL_UnlockSurface, SDL_WriteLE16, and SDL_WriteLE32.