src/video/SDL_surface.c

/*
    SDL - Simple DirectMedia Layer
    Copyright (C) 1997-2006 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"

#include "SDL_video.h"
#include "SDL_compat.h"
#include "SDL_sysvideo.h"
#include "SDL_blit.h"
#include "SDL_RLEaccel_c.h"
#include "SDL_pixels_c.h"
#include "SDL_leaks.h"


/* Public routines */
/*
 * Create an empty RGB surface of the appropriate depth
 */
SDL_Surface *
SDL_CreateRGBSurface(Uint32 flags,
                     int width, int height, int depth,
                     Uint32 Rmask, Uint32 Gmask, Uint32 Bmask, Uint32 Amask)
{
    SDL_Surface *surface;

    /* FIXME!! */
    /* Make sure the size requested doesn't overflow our datatypes */
    /* Next time I write a library like SDL, I'll use int for size. :) */
    if (width >= 16384 || height >= 65536) {
        SDL_SetError("Width or height is too large");
        return NULL;
    }

    /* Allocate the surface */
    surface = (SDL_Surface *) SDL_malloc(sizeof(*surface));
    if (surface == NULL) {
        SDL_OutOfMemory();
        return NULL;
    }
    SDL_zerop(surface);

    surface->format = SDL_AllocFormat(depth, Rmask, Gmask, Bmask, Amask);
    if (!surface->format) {
        SDL_FreeSurface(surface);
        return NULL;
    }
    if (Amask) {
        surface->flags |= SDL_SRCALPHA;
    }
    surface->w = width;
    surface->h = height;
    surface->pitch = SDL_CalculatePitch(surface);
    SDL_SetClipRect(surface, NULL);

    if (surface->format->BitsPerPixel <= 8) {
        SDL_Palette *palette =
            SDL_AllocPalette((1 << surface->format->BitsPerPixel));
        if (!palette) {
            SDL_FreeSurface(surface);
            return NULL;
        }
        if (Rmask || Bmask || Gmask) {
            const SDL_PixelFormat *format = surface->format;

            /* create palette according to masks */
            int i;
            int Rm = 0, Gm = 0, Bm = 0;
            int Rw = 0, Gw = 0, Bw = 0;

            if (Rmask) {
                Rw = 8 - format->Rloss;
                for (i = format->Rloss; i > 0; i -= Rw)
                    Rm |= 1 << i;
            }
            if (Gmask) {
                Gw = 8 - format->Gloss;
                for (i = format->Gloss; i > 0; i -= Gw)
                    Gm |= 1 << i;
            }
            if (Bmask) {
                Bw = 8 - format->Bloss;
                for (i = format->Bloss; i > 0; i -= Bw)
                    Bm |= 1 << i;
            }
            for (i = 0; i < palette->ncolors; ++i) {
                int r, g, b;
                r = (i & Rmask) >> format->Rshift;
                r = (r << format->Rloss) | ((r * Rm) >> Rw);
                palette->colors[i].r = r;

                g = (i & Gmask) >> format->Gshift;
                g = (g << format->Gloss) | ((g * Gm) >> Gw);
                palette->colors[i].g = g;

                b = (i & Bmask) >> format->Bshift;
                b = (b << format->Bloss) | ((b * Bm) >> Bw);
                palette->colors[i].b = b;
            }
        } else if (palette->ncolors == 2) {
            /* Create a black and white bitmap palette */
            palette->colors[0].r = 0xFF;
            palette->colors[0].g = 0xFF;
            palette->colors[0].b = 0xFF;
            palette->colors[1].r = 0x00;
            palette->colors[1].g = 0x00;
            palette->colors[1].b = 0x00;
        }
        SDL_SetSurfacePalette(surface, palette);
        SDL_FreePalette(palette);
    }

    /* Get the pixels */
    if (surface->w && surface->h) {
        surface->pixels = SDL_malloc(surface->h * surface->pitch);
        if (!surface->pixels) {
            SDL_FreeSurface(surface);
            SDL_OutOfMemory();
            return NULL;
        }
        /* This is important for bitmaps */
        SDL_memset(surface->pixels, 0, surface->h * surface->pitch);
    }

    /* Allocate an empty mapping */
    surface->map = SDL_AllocBlitMap();
    if (!surface->map) {
        SDL_FreeSurface(surface);
        return NULL;
    }
    SDL_FormatChanged(surface);

    /* The surface is ready to go */
    surface->refcount = 1;
#ifdef CHECK_LEAKS
    ++surfaces_allocated;
#endif
    return surface;
}

/*
 * Create an RGB surface from an existing memory buffer
 */
SDL_Surface *
SDL_CreateRGBSurfaceFrom(void *pixels,
                         int width, int height, int depth, int pitch,
                         Uint32 Rmask, Uint32 Gmask, Uint32 Bmask,
                         Uint32 Amask)
{
    SDL_Surface *surface;

    surface =
        SDL_CreateRGBSurface(0, 0, 0, depth, Rmask, Gmask, Bmask, Amask);
    if (surface != NULL) {
        surface->flags |= SDL_PREALLOC;
        surface->pixels = pixels;
        surface->w = width;
        surface->h = height;
        surface->pitch = pitch;
        SDL_SetClipRect(surface, NULL);
    }
    return surface;
}

SDL_Surface *
SDL_CreateRGBSurfaceFromTexture(SDL_TextureID textureID)
{
    SDL_Surface *surface;
    Uint32 format;
    int w, h;
    int bpp;
    Uint32 Rmask, Gmask, Bmask, Amask;
    void *pixels;
    int pitch;

    if (SDL_QueryTexture(textureID, &format, NULL, &w, &h) < 0) {
        return NULL;
    }

    if (!SDL_PixelFormatEnumToMasks
        (format, &bpp, &Rmask, &Gmask, &Bmask, &Amask)) {
        SDL_SetError("Unknown texture format");
        return NULL;
    }

    if (SDL_QueryTexturePixels(textureID, &pixels, &pitch) == 0) {
        surface =
            SDL_CreateRGBSurfaceFrom(pixels, w, h, bpp, pitch, Rmask, Gmask,
                                     Bmask, Amask);
    } else {
        surface =
            SDL_CreateRGBSurface(0, 0, 0, bpp, Rmask, Gmask, Bmask, Amask);
        if (surface) {
            surface->flags |= SDL_HWSURFACE;
            surface->w = w;
            surface->h = h;
            SDL_SetClipRect(surface, NULL);
        }
    }
    if (surface) {
        surface->textureID = textureID;
    }

    return surface;
}

static int
SDL_SurfacePaletteChanged(void *userdata, SDL_Palette * palette)
{
    SDL_Surface *surface = (SDL_Surface *) userdata;

    if (surface->textureID) {
        if (SDL_SetTexturePalette
            (surface->textureID, palette->colors, 0, palette->ncolors) < 0) {
            SDL_GetTexturePalette(surface->textureID, palette->colors, 0,
                                  palette->ncolors);
            return -1;
        }
    }
    SDL_FormatChanged(surface);

    return 0;
}

int
SDL_SetSurfacePalette(SDL_Surface * surface, SDL_Palette * palette)
{
    if (!surface || !surface->format) {
        SDL_SetError("SDL_SetSurfacePalette() passed a NULL surface");
        return -1;
    }

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

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

    if (surface->format->palette) {
        SDL_DelPaletteWatch(surface->format->palette,
                            SDL_SurfacePaletteChanged, surface);
    }

    surface->format->palette = palette;

    if (surface->format->palette) {
        SDL_AddPaletteWatch(surface->format->palette,
                            SDL_SurfacePaletteChanged, surface);
    }
    return 0;
}

/*
 * Set the color key in a blittable surface
 */
int
SDL_SetColorKey(SDL_Surface * surface, Uint32 flag, Uint32 key)
{
    /* Sanity check the flag as it gets passed in */
    if (flag & SDL_SRCCOLORKEY) {
        if (flag & (SDL_RLEACCEL | SDL_RLEACCELOK)) {
            flag = (SDL_SRCCOLORKEY | SDL_RLEACCELOK);
        } else {
            flag = SDL_SRCCOLORKEY;
        }
    } else {
        flag = 0;
    }

    /* Optimize away operations that don't change anything */
    if ((flag == (surface->flags & (SDL_SRCCOLORKEY | SDL_RLEACCELOK))) &&
        (key == surface->format->colorkey)) {
        return (0);
    }

    /* UnRLE surfaces before we change the colorkey */
    if (surface->flags & SDL_RLEACCEL) {
        SDL_UnRLESurface(surface, 1);
    }

    if (flag) {
        surface->flags |= SDL_SRCCOLORKEY;
        surface->format->colorkey = key;
        if (flag & SDL_RLEACCELOK) {
            surface->flags |= SDL_RLEACCELOK;
        } else {
            surface->flags &= ~SDL_RLEACCELOK;
        }
    } else {
        surface->flags &= ~(SDL_SRCCOLORKEY | SDL_RLEACCELOK);
        surface->format->colorkey = 0;
    }
    SDL_InvalidateMap(surface->map);
    return (0);
}

/* This function sets the alpha channel of a surface */
int
SDL_SetAlpha(SDL_Surface * surface, Uint32 flag, Uint8 value)
{
    Uint32 oldflags = surface->flags;
    Uint32 oldalpha = surface->format->alpha;

    /* Sanity check the flag as it gets passed in */
    if (flag & SDL_SRCALPHA) {
        if (flag & (SDL_RLEACCEL | SDL_RLEACCELOK)) {
            flag = (SDL_SRCALPHA | SDL_RLEACCELOK);
        } else {
            flag = SDL_SRCALPHA;
        }
    } else {
        flag = 0;
    }

    /* Optimize away operations that don't change anything */
    if ((flag == (surface->flags & (SDL_SRCALPHA | SDL_RLEACCELOK))) &&
        (!flag || value == oldalpha)) {
        return (0);
    }

    if (!(flag & SDL_RLEACCELOK) && (surface->flags & SDL_RLEACCEL))
        SDL_UnRLESurface(surface, 1);

    if (flag) {
        surface->flags |= SDL_SRCALPHA;
        surface->format->alpha = value;
        if (flag & SDL_RLEACCELOK) {
            surface->flags |= SDL_RLEACCELOK;
        } else {
            surface->flags &= ~SDL_RLEACCELOK;
        }
    } else {
        surface->flags &= ~SDL_SRCALPHA;
        surface->format->alpha = SDL_ALPHA_OPAQUE;
    }
    /*
     * The representation for software surfaces is independent of
     * per-surface alpha, so no need to invalidate the blit mapping
     * if just the alpha value was changed. (If either is 255, we still
     * need to invalidate.)
     */
    if (oldflags != surface->flags
        || (((oldalpha + 1) ^ (value + 1)) & 0x100)) {
        SDL_InvalidateMap(surface->map);
    }
    return (0);
}

int
SDL_SetAlphaChannel(SDL_Surface * surface, Uint8 value)
{
    int row, col;
    int offset;
    Uint8 *buf;

    if ((surface->format->Amask != 0xFF000000) &&
        (surface->format->Amask != 0x000000FF)) {
        SDL_SetError("Unsupported surface alpha mask format");
        return -1;
    }
#if SDL_BYTEORDER == SDL_LIL_ENDIAN
    if (surface->format->Amask == 0xFF000000) {
        offset = 3;
    } else {
        offset = 0;
    }
#else
    if (surface->format->Amask == 0xFF000000) {
        offset = 0;
    } else {
        offset = 3;
    }
#endif /* Byte ordering */

    /* Quickly set the alpha channel of an RGBA or ARGB surface */
    if (SDL_MUSTLOCK(surface)) {
        if (SDL_LockSurface(surface) < 0) {
            return -1;
        }
    }
    row = surface->h;
    while (row--) {
        col = surface->w;
        buf = (Uint8 *) surface->pixels + row * surface->pitch + offset;
        while (col--) {
            *buf = value;
            buf += 4;
        }
    }
    if (SDL_MUSTLOCK(surface)) {
        SDL_UnlockSurface(surface);
    }
    return 0;
}

/*
 * A function to calculate the intersection of two rectangles:
 * return true if the rectangles intersect, false otherwise
 */
static __inline__ SDL_bool
SDL_IntersectRect(const SDL_Rect * A, const SDL_Rect * B,
                  SDL_Rect * intersection)
{
    int Amin, Amax, Bmin, Bmax;

    /* Horizontal intersection */
    Amin = A->x;
    Amax = Amin + A->w;
    Bmin = B->x;
    Bmax = Bmin + B->w;
    if (Bmin > Amin)
        Amin = Bmin;
    intersection->x = Amin;
    if (Bmax < Amax)
        Amax = Bmax;
    intersection->w = Amax - Amin > 0 ? Amax - Amin : 0;

    /* Vertical intersection */
    Amin = A->y;
    Amax = Amin + A->h;
    Bmin = B->y;
    Bmax = Bmin + B->h;
    if (Bmin > Amin)
        Amin = Bmin;
    intersection->y = Amin;
    if (Bmax < Amax)
        Amax = Bmax;
    intersection->h = Amax - Amin > 0 ? Amax - Amin : 0;

    return (intersection->w && intersection->h);
}

/*
 * Set the clipping rectangle for a blittable surface
 */
SDL_bool
SDL_SetClipRect(SDL_Surface * surface, const SDL_Rect * rect)
{
    SDL_Rect full_rect;

    /* Don't do anything if there's no surface to act on */
    if (!surface) {
        return SDL_FALSE;
    }

    /* Set up the full surface rectangle */
    full_rect.x = 0;
    full_rect.y = 0;
    full_rect.w = surface->w;
    full_rect.h = surface->h;

    /* Set the clipping rectangle */
    if (!rect) {
        surface->clip_rect = full_rect;
        return 1;
    }
    return SDL_IntersectRect(rect, &full_rect, &surface->clip_rect);
}

void
SDL_GetClipRect(SDL_Surface * surface, SDL_Rect * rect)
{
    if (surface && rect) {
        *rect = surface->clip_rect;
    }
}

/* 
 * Set up a blit between two surfaces -- split into three parts:
 * The upper part, SDL_UpperBlit(), performs clipping and rectangle 
 * verification.  The lower part is a pointer to a low level
 * accelerated blitting function.
 *
 * These parts are separated out and each used internally by this 
 * library in the optimimum places.  They are exported so that if
 * you know exactly what you are doing, you can optimize your code
 * by calling the one(s) you need.
 */
int
SDL_LowerBlit(SDL_Surface * src, SDL_Rect * srcrect,
              SDL_Surface * dst, SDL_Rect * dstrect)
{
    /* Check to make sure the blit mapping is valid */
    if ((src->map->dst != dst) ||
        (src->map->dst->format_version != src->map->format_version)) {
        if (SDL_MapSurface(src, dst) < 0) {
            return (-1);
        }
    }
    return (src->map->sw_blit(src, srcrect, dst, dstrect));
}


int
SDL_UpperBlit(SDL_Surface * src, SDL_Rect * srcrect,
              SDL_Surface * dst, SDL_Rect * dstrect)
{
    SDL_Rect fulldst;
    int srcx, srcy, w, h;

    /* Make sure the surfaces aren't locked */
    if (!src || !dst) {
        SDL_SetError("SDL_UpperBlit: passed a NULL surface");
        return (-1);
    }
    if (src->locked || dst->locked) {
        SDL_SetError("Surfaces must not be locked during blit");
        return (-1);
    }

    /* If the destination rectangle is NULL, use the entire dest surface */
    if (dstrect == NULL) {
        fulldst.x = fulldst.y = 0;
        dstrect = &fulldst;
    }

    /* clip the source rectangle to the source surface */
    if (srcrect) {
        int maxw, maxh;

        srcx = srcrect->x;
        w = srcrect->w;
        if (srcx < 0) {
            w += srcx;
            dstrect->x -= srcx;
            srcx = 0;
        }
        maxw = src->w - srcx;
        if (maxw < w)
            w = maxw;

        srcy = srcrect->y;
        h = srcrect->h;
        if (srcy < 0) {
            h += srcy;
            dstrect->y -= srcy;
            srcy = 0;
        }
        maxh = src->h - srcy;
        if (maxh < h)
            h = maxh;

    } else {
        srcx = srcy = 0;
        w = src->w;
        h = src->h;
    }

    /* clip the destination rectangle against the clip rectangle */
    {
        SDL_Rect *clip = &dst->clip_rect;
        int dx, dy;

        dx = clip->x - dstrect->x;
        if (dx > 0) {
            w -= dx;
            dstrect->x += dx;
            srcx += dx;
        }
        dx = dstrect->x + w - clip->x - clip->w;
        if (dx > 0)
            w -= dx;

        dy = clip->y - dstrect->y;
        if (dy > 0) {
            h -= dy;
            dstrect->y += dy;
            srcy += dy;
        }
        dy = dstrect->y + h - clip->y - clip->h;
        if (dy > 0)
            h -= dy;
    }

    if (w > 0 && h > 0) {
        SDL_Rect sr;
        sr.x = srcx;
        sr.y = srcy;
        sr.w = dstrect->w = w;
        sr.h = dstrect->h = h;
        return SDL_LowerBlit(src, &sr, dst, dstrect);
    }
    dstrect->w = dstrect->h = 0;
    return 0;
}

static int
SDL_FillRect1(SDL_Surface * dst, SDL_Rect * dstrect, Uint32 color)
{
    /* FIXME: We have to worry about packing order.. *sigh* */
    SDL_SetError("1-bpp rect fill not yet implemented");
    return -1;
}

static int
SDL_FillRect4(SDL_Surface * dst, SDL_Rect * dstrect, Uint32 color)
{
    /* FIXME: We have to worry about packing order.. *sigh* */
    SDL_SetError("4-bpp rect fill not yet implemented");
    return -1;
}

/* 
 * This function performs a fast fill of the given rectangle with 'color'
 */
int
SDL_FillRect(SDL_Surface * dst, SDL_Rect * dstrect, Uint32 color)
{
    int x, y;
    Uint8 *row;

    /* This function doesn't work on surfaces < 8 bpp */
    if (dst->format->BitsPerPixel < 8) {
        switch (dst->format->BitsPerPixel) {
        case 1:
            return SDL_FillRect1(dst, dstrect, color);
            break;
        case 4:
            return SDL_FillRect4(dst, dstrect, color);
            break;
        default:
            SDL_SetError("Fill rect on unsupported surface format");
            return (-1);
            break;
        }
    }

    /* If 'dstrect' == NULL, then fill the whole surface */
    if (dstrect) {
        /* Perform clipping */
        if (!SDL_IntersectRect(dstrect, &dst->clip_rect, dstrect)) {
            return (0);
        }
    } else {
        dstrect = &dst->clip_rect;
    }

    /* Perform software fill */
    if (SDL_LockSurface(dst) != 0) {
        return (-1);
    }
    row = (Uint8 *) dst->pixels + dstrect->y * dst->pitch +
        dstrect->x * dst->format->BytesPerPixel;
    if (dst->format->palette || (color == 0)) {
        x = dstrect->w * dst->format->BytesPerPixel;
        if (!color && !((uintptr_t) row & 3) && !(x & 3)
            && !(dst->pitch & 3)) {
            int n = x >> 2;
            for (y = dstrect->h; y; --y) {
                SDL_memset4(row, 0, n);
                row += dst->pitch;
            }
        } else {
#ifdef __powerpc__
            /*
             * SDL_memset() on PPC (both glibc and codewarrior) uses
             * the dcbz (Data Cache Block Zero) instruction, which
             * causes an alignment exception if the destination is
             * uncachable, so only use it on software surfaces
             */
            if (dst->flags & SDL_HWSURFACE) {
                if (dstrect->w >= 8) {
                    /*
                     * 64-bit stores are probably most
                     * efficient to uncached video memory
                     */
                    double fill;
                    SDL_memset(&fill, color, (sizeof fill));
                    for (y = dstrect->h; y; y--) {
                        Uint8 *d = row;
                        unsigned n = x;
                        unsigned nn;
                        Uint8 c = color;
                        double f = fill;
                        while ((unsigned long) d & (sizeof(double) - 1)) {
                            *d++ = c;
                            n--;
                        }
                        nn = n / (sizeof(double) * 4);
                        while (nn) {
                            ((double *) d)[0] = f;
                            ((double *) d)[1] = f;
                            ((double *) d)[2] = f;
                            ((double *) d)[3] = f;
                            d += 4 * sizeof(double);
                            nn--;
                        }
                        n &= ~(sizeof(double) * 4 - 1);
                        nn = n / sizeof(double);
                        while (nn) {
                            *(double *) d = f;
                            d += sizeof(double);
                            nn--;
                        }
                        n &= ~(sizeof(double) - 1);
                        while (n) {
                            *d++ = c;
                            n--;
                        }
                        row += dst->pitch;
                    }
                } else {
                    /* narrow boxes */
                    for (y = dstrect->h; y; y--) {
                        Uint8 *d = row;
                        Uint8 c = color;
                        int n = x;
                        while (n) {
                            *d++ = c;
                            n--;
                        }
                        row += dst->pitch;
                    }
                }
            } else
#endif /* __powerpc__ */
            {
                for (y = dstrect->h; y; y--) {
                    SDL_memset(row, color, x);
                    row += dst->pitch;
                }
            }
        }
    } else {
        switch (dst->format->BytesPerPixel) {
        case 2:
            for (y = dstrect->h; y; --y) {
                Uint16 *pixels = (Uint16 *) row;
                Uint16 c = (Uint16) color;
                Uint32 cc = (Uint32) c << 16 | c;
                int n = dstrect->w;
                if ((uintptr_t) pixels & 3) {
                    *pixels++ = c;
                    n--;
                }
                if (n >> 1)
                    SDL_memset4(pixels, cc, n >> 1);
                if (n & 1)
                    pixels[n - 1] = c;
                row += dst->pitch;
            }
            break;

        case 3:
#if SDL_BYTEORDER == SDL_BIG_ENDIAN
            color <<= 8;
#endif
            for (y = dstrect->h; y; --y) {
                Uint8 *pixels = row;
                for (x = dstrect->w; x; --x) {
                    SDL_memcpy(pixels, &color, 3);
                    pixels += 3;
                }
                row += dst->pitch;
            }
            break;

        case 4:
            for (y = dstrect->h; y; --y) {
                SDL_memset4(row, color, dstrect->w);
                row += dst->pitch;
            }
            break;
        }
    }
    SDL_UnlockSurface(dst);

    /* We're done! */
    return (0);
}

/*
 * Lock a surface to directly access the pixels
 */
int
SDL_LockSurface(SDL_Surface * surface)
{
    if (!surface->locked) {
        /* Perform the lock */
        if (surface->flags & SDL_HWSURFACE) {
            if (SDL_LockTexture
                (surface->textureID, NULL, 1, &surface->pixels,
                 &surface->pitch) < 0) {
                return (-1);
            }
        }
        if (surface->flags & SDL_RLEACCEL) {
            SDL_UnRLESurface(surface, 1);
            surface->flags |= SDL_RLEACCEL;     /* save accel'd state */
        }
    }

    /* Increment the surface lock count, for recursive locks */
    ++surface->locked;

    /* Ready to go.. */
    return (0);
}

/*
 * Unlock a previously locked surface
 */
void
SDL_UnlockSurface(SDL_Surface * surface)
{
    /* Only perform an unlock if we are locked */
    if (!surface->locked || (--surface->locked > 0)) {
        return;
    }

    /* Unlock hardware or accelerated surfaces */
    if (surface->flags & SDL_HWSURFACE) {
        SDL_UnlockTexture(surface->textureID);
    }

    /* Update RLE encoded surface with new data */
    if ((surface->flags & SDL_RLEACCEL) == SDL_RLEACCEL) {
        surface->flags &= ~SDL_RLEACCEL;        /* stop lying */
        SDL_RLESurface(surface);
    }
}

/* 
 * Convert a surface into the specified pixel format.
 */
SDL_Surface *
SDL_ConvertSurface(SDL_Surface * surface,
                   SDL_PixelFormat * format, Uint32 flags)
{
    SDL_Surface *convert;
    Uint32 colorkey = 0;
    Uint8 alpha = 0;
    Uint32 surface_flags;
    SDL_Rect bounds;

    /* Check for empty destination palette! (results in empty image) */
    if (format->palette != NULL) {
        int i;
        for (i = 0; i < format->palette->ncolors; ++i) {
            if ((format->palette->colors[i].r != 0xFF) ||
                (format->palette->colors[i].g != 0xFF) ||
                (format->palette->colors[i].b != 0xFF))
                break;
        }
        if (i == format->palette->ncolors) {
            SDL_SetError("Empty destination palette");
            return (NULL);
        }
    }

    /* Create a new surface with the desired format */
    convert = SDL_CreateRGBSurface(flags,
                                   surface->w, surface->h,
                                   format->BitsPerPixel, format->Rmask,
                                   format->Gmask, format->Bmask,
                                   format->Amask);
    if (convert == NULL) {
        return (NULL);
    }

    /* Copy the palette if any */
    if (format->palette && convert->format->palette) {
        SDL_memcpy(convert->format->palette->colors,
                   format->palette->colors,
                   format->palette->ncolors * sizeof(SDL_Color));
        convert->format->palette->ncolors = format->palette->ncolors;
    }

    /* Save the original surface color key and alpha */
    surface_flags = surface->flags;
    if ((surface_flags & SDL_SRCCOLORKEY) == SDL_SRCCOLORKEY) {
        /* Convert colourkeyed surfaces to RGBA if requested */
        if ((flags & SDL_SRCCOLORKEY) != SDL_SRCCOLORKEY && format->Amask) {
            surface_flags &= ~SDL_SRCCOLORKEY;
        } else {
            colorkey = surface->format->colorkey;
            SDL_SetColorKey(surface, 0, 0);
        }
    }
    if ((surface_flags & SDL_SRCALPHA) == SDL_SRCALPHA) {
        /* Copy over the alpha channel to RGBA if requested */
        if (format->Amask) {
            surface->flags &= ~SDL_SRCALPHA;
        } else {
            alpha = surface->format->alpha;
            SDL_SetAlpha(surface, 0, 0);
        }
    }

    /* Copy over the image data */
    bounds.x = 0;
    bounds.y = 0;
    bounds.w = surface->w;
    bounds.h = surface->h;
    SDL_LowerBlit(surface, &bounds, convert, &bounds);

    /* Clean up the original surface, and update converted surface */
    if (convert != NULL) {
        SDL_SetClipRect(convert, &surface->clip_rect);
    }
    if ((surface_flags & SDL_SRCCOLORKEY) == SDL_SRCCOLORKEY) {
        Uint32 cflags = surface_flags & (SDL_SRCCOLORKEY | SDL_RLEACCELOK);
        if (convert != NULL) {
            Uint8 keyR, keyG, keyB;

            SDL_GetRGB(colorkey, surface->format, &keyR, &keyG, &keyB);
            SDL_SetColorKey(convert, cflags | (flags & SDL_RLEACCELOK),
                            SDL_MapRGB(convert->format, keyR, keyG, keyB));
        }
        SDL_SetColorKey(surface, cflags, colorkey);
    }
    if ((surface_flags & SDL_SRCALPHA) == SDL_SRCALPHA) {
        Uint32 aflags = surface_flags & (SDL_SRCALPHA | SDL_RLEACCELOK);
        if (convert != NULL) {
            SDL_SetAlpha(convert, aflags | (flags & SDL_RLEACCELOK), alpha);
        }
        if (format->Amask) {
            surface->flags |= SDL_SRCALPHA;
        } else {
            SDL_SetAlpha(surface, aflags, alpha);
        }
    }

    /* We're ready to go! */
    return (convert);
}

/*
 * Free a surface created by the above function.
 */
void
SDL_FreeSurface(SDL_Surface * surface)
{
    if (surface == NULL) {
        return;
    }
    if (--surface->refcount > 0) {
        return;
    }
    while (surface->locked > 0) {
        SDL_UnlockSurface(surface);
    }
    if (surface->flags & SDL_RLEACCEL) {
        SDL_UnRLESurface(surface, 0);
    }
    if (surface->format) {
        SDL_SetSurfacePalette(surface, NULL);
        SDL_FreeFormat(surface->format);
        surface->format = NULL;
    }
    if (surface->map != NULL) {
        SDL_FreeBlitMap(surface->map);
        surface->map = NULL;
    }
    /* Should we destroy the texture too?
       if (surface->textureID) {
       SDL_DestroyTexture(surface->textureID);
       }
     */
    if (surface->pixels && ((surface->flags & SDL_PREALLOC) != SDL_PREALLOC)) {
        SDL_free(surface->pixels);
    }
    SDL_free(surface);
#ifdef CHECK_LEAKS
    --surfaces_allocated;
#endif
}

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