IMG_xcf.c

/*
  SDL_image:  An example image loading library for use with SDL
  Copyright (C) 1997-2020 Sam Lantinga <slouken@libsdl.org>

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.
*/

/* This is a XCF image file loading framework */

#include "SDL_endian.h"
#include "SDL_image.h"

#ifdef LOAD_XCF

#if DEBUG
static char prop_names [][30] = {
  "end",
  "colormap",
  "active_layer",
  "active_channel",
  "selection",
  "floating_selection",
  "opacity",
  "mode",
  "visible",
  "linked",
  "preserve_transparency",
  "apply_mask",
  "edit_mask",
  "show_mask",
  "show_masked",
  "offsets",
  "color",
  "compression",
  "guides",
  "resolution",
  "tattoo",
  "parasites",
  "unit",
  "paths",
  "user_unit"
};
#endif


typedef enum
{
  PROP_END = 0,
  PROP_COLORMAP = 1,
  PROP_ACTIVE_LAYER = 2,
  PROP_ACTIVE_CHANNEL = 3,
  PROP_SELECTION = 4,
  PROP_FLOATING_SELECTION = 5,
  PROP_OPACITY = 6,
  PROP_MODE = 7,
  PROP_VISIBLE = 8,
  PROP_LINKED = 9,
  PROP_PRESERVE_TRANSPARENCY = 10,
  PROP_APPLY_MASK = 11,
  PROP_EDIT_MASK = 12,
  PROP_SHOW_MASK = 13,
  PROP_SHOW_MASKED = 14,
  PROP_OFFSETS = 15,
  PROP_COLOR = 16,
  PROP_COMPRESSION = 17,
  PROP_GUIDES = 18,
  PROP_RESOLUTION = 19,
  PROP_TATTOO = 20,
  PROP_PARASITES = 21,
  PROP_UNIT = 22,
  PROP_PATHS = 23,
  PROP_USER_UNIT = 24
} xcf_prop_type;

typedef enum {
  COMPR_NONE    = 0,
  COMPR_RLE     = 1,
  COMPR_ZLIB    = 2,
  COMPR_FRACTAL = 3
} xcf_compr_type;

typedef enum {
  IMAGE_RGB       = 0,
  IMAGE_GREYSCALE = 1,
  IMAGE_INDEXED   = 2
} xcf_image_type;

typedef struct {
  Uint32 id;
  Uint32 length;
  union {
    struct {
      Uint32 num;
      char * cmap;
    } colormap; // 1
    struct {
      Uint32 drawable_offset;
    } floating_selection; // 5
    Sint32 opacity;
    Sint32 mode;
    int    visible;
    int    linked;
    int    preserve_transparency;
    int    apply_mask;
    int    show_mask;
    struct {
      Sint32 x;
      Sint32 y;
    } offset;
    unsigned char color [3];
    Uint8 compression;
    struct {
      Sint32 x;
      Sint32 y;
    } resolution;
    struct {
      char * name;
      Uint32 flags;
      Uint32 size;
      char * data;
    } parasite;
  } data;
} xcf_prop;

typedef struct {
  char   sign [14];
  Uint32 file_version;
  Uint32 width;
  Uint32 height;
  Sint32 image_type;
  Uint32 precision;
  xcf_prop * properties;

  Uint32 * layer_file_offsets;
  Uint32 * channel_file_offsets;

  xcf_compr_type compr;
  Uint32         cm_num;
  unsigned char * cm_map;
} xcf_header;

typedef struct {
  Uint32 width;
  Uint32 height;
  Sint32 layer_type;
  char * name;
  xcf_prop * properties;

  Uint32 hierarchy_file_offset;
  Uint32 layer_mask_offset;

  Uint32 offset_x;
  Uint32 offset_y;
  int visible;
} xcf_layer;

typedef struct {
  Uint32 width;
  Uint32 height;
  char * name;
  xcf_prop * properties;

  Uint32 hierarchy_file_offset;

  Uint32 color;
  Uint32 opacity;
  int selection;
  int visible;
} xcf_channel;

typedef struct {
  Uint32 width;
  Uint32 height;
  Uint32 bpp;

  Uint32 * level_file_offsets;
} xcf_hierarchy;

typedef struct {
  Uint32 width;
  Uint32 height;

  Uint32 * tile_file_offsets;
} xcf_level;

typedef unsigned char * xcf_tile;

typedef unsigned char * (* load_tile_type) (SDL_RWops *, Uint32, int, int, int);


/* See if an image is contained in a data source */
int IMG_isXCF(SDL_RWops *src)
{
    Sint64 start;
    int is_XCF;
    char magic[14];

    if ( !src )
        return 0;
    start = SDL_RWtell(src);
    is_XCF = 0;
    if ( SDL_RWread(src, magic, sizeof(magic), 1) ) {
        if (SDL_strncmp(magic, "gimp xcf ", 9) == 0) {
            is_XCF = 1;
        }
    }
    SDL_RWseek(src, start, RW_SEEK_SET);
    return(is_XCF);
}

static char * read_string (SDL_RWops * src) {
  Sint64 remaining;
  Uint32 tmp;
  char * data;

  tmp = SDL_ReadBE32(src);
  remaining = SDL_RWsize(src) - SDL_RWtell(src);
  if (tmp > 0 && (Sint32)tmp <= remaining) {
    data = (char *) SDL_malloc (sizeof (char) * tmp);
    if (data) {
      SDL_RWread(src, data, tmp, 1);
      data[tmp - 1] = '\0';
    }
  }
  else {
    data = NULL;
  }
  return data;
}

static Uint64 read_offset (SDL_RWops * src, const xcf_header * h) {
  Uint64 offset;  // starting with version 11, offsets are 64 bits
  offset = (h->file_version >= 11) ? (Uint64)SDL_ReadBE32 (src) << 32 : 0;
  offset |= SDL_ReadBE32 (src);
  return offset;
}


static Uint32 Swap32 (Uint32 v) {
  return
    ((v & 0x000000FF) << 16)
    |  ((v & 0x0000FF00))
    |  ((v & 0x00FF0000) >> 16)
    |  ((v & 0xFF000000));
}

static int xcf_read_property (SDL_RWops * src, xcf_prop * prop) {
  Uint32 len;
  prop->id = SDL_ReadBE32 (src);
  prop->length = SDL_ReadBE32 (src);

#if DEBUG
  printf ("%.8X: %s(%u): %u\n", SDL_RWtell (src), prop->id < 25 ? prop_names [prop->id] : "unknown", prop->id, prop->length);
#endif

  switch (prop->id) {
  case PROP_COLORMAP:
    prop->data.colormap.num = SDL_ReadBE32 (src);
    prop->data.colormap.cmap = (char *) SDL_malloc (sizeof (char) * prop->data.colormap.num * 3);
    SDL_RWread (src, prop->data.colormap.cmap, prop->data.colormap.num*3, 1);
    break;

  case PROP_OFFSETS:
    prop->data.offset.x = SDL_ReadBE32 (src);
    prop->data.offset.y = SDL_ReadBE32 (src);
    break;
  case PROP_OPACITY:
    prop->data.opacity = SDL_ReadBE32 (src);
    break;
  case PROP_COMPRESSION:
  case PROP_COLOR:
    if (prop->length > sizeof(prop->data)) {
        len = sizeof(prop->data);
    } else {
        len = prop->length;
    }
    SDL_RWread(src, &prop->data, len, 1);
    break;
  case PROP_VISIBLE:
    prop->data.visible = SDL_ReadBE32 (src);
    break;
  default:
    //    SDL_RWread (src, &prop->data, prop->length, 1);
    if (SDL_RWseek (src, prop->length, RW_SEEK_CUR) < 0)
      return 0;  // ERROR
  }
  return 1;  // OK
}

static void free_xcf_header (xcf_header * h) {
  if (h->cm_num)
    SDL_free (h->cm_map);
  if (h->layer_file_offsets)
    SDL_free (h->layer_file_offsets);
  SDL_free (h);
}

static xcf_header * read_xcf_header (SDL_RWops * src) {
  xcf_header * h;
  xcf_prop prop;

  h = (xcf_header *) SDL_malloc (sizeof (xcf_header));
  if (!h) {
    return NULL;
  }
  SDL_RWread (src, h->sign, 14, 1);
  h->width       = SDL_ReadBE32 (src);
  h->height      = SDL_ReadBE32 (src);
  h->image_type  = SDL_ReadBE32 (src);
  if (h->sign[9] == 'v' && h->sign[10] >= '0' && h->sign[10] <= '9' && h->sign[11] >= '0' && h->sign[11] <= '9' && h->sign[12] >= '0' && h->sign[12] <= '9')
    h->file_version = (h->sign[10] - '0') * 100 + (h->sign[11] - '0') * 10 + (h->sign[12] - '0');
  else
    h->file_version = 0;
#ifdef DEBUG
  printf ("XCF signature : %.14s (version %u)\n", h->sign, h->file_version);
  printf (" (%u,%u) type=%u\n", h->width, h->height, h->image_type);
#endif
  if (h->file_version >= 4)
    h->precision = SDL_ReadBE32 (src);
  else
    h->precision = 150;

  h->properties = NULL;
  h->layer_file_offsets = NULL;
  h->compr      = COMPR_NONE;
  h->cm_num = 0;
  h->cm_map = NULL;

  // Just read, don't save
  do {
    if (!xcf_read_property (src, &prop)) {
      free_xcf_header (h);
      return NULL;
    }
    if (prop.id == PROP_COMPRESSION)
      h->compr = (xcf_compr_type)prop.data.compression;
    else if (prop.id == PROP_COLORMAP) {
      // unused var: int i;
      Uint32 cm_num;
      unsigned char *cm_map;

      cm_num = prop.data.colormap.num;
      cm_map = (unsigned char *) SDL_realloc(h->cm_map, sizeof (unsigned char) * 3 * cm_num);
      if (cm_map) {
        h->cm_num = cm_num;
        h->cm_map = cm_map;
        SDL_memcpy (h->cm_map, prop.data.colormap.cmap, 3*sizeof (char)*h->cm_num);
      }
      SDL_free (prop.data.colormap.cmap);

      if (!cm_map) {
        free_xcf_header(h);
        return NULL;
      }
    }
  } while (prop.id != PROP_END);

  return h;
}

static void free_xcf_layer (xcf_layer * l) {
  SDL_free (l->name);
  SDL_free (l);
}

static xcf_layer * read_xcf_layer (SDL_RWops * src, const xcf_header * h) {
  xcf_layer * l;
  xcf_prop    prop;

  l = (xcf_layer *) SDL_malloc (sizeof (xcf_layer));
  l->width  = SDL_ReadBE32 (src);
  l->height = SDL_ReadBE32 (src);
  l->layer_type = SDL_ReadBE32 (src);

  l->name = read_string (src);
#ifdef DEBUG
  printf ("layer (%d,%d) type=%d '%s'\n", l->width, l->height, l->layer_type, l->name);
#endif

  do {
    if (!xcf_read_property (src, &prop)) {
      free_xcf_layer (l);
      return NULL;
    }
    if (prop.id == PROP_OFFSETS) {
      l->offset_x = prop.data.offset.x;
      l->offset_y = prop.data.offset.y;
    } else if (prop.id == PROP_VISIBLE) {
      l->visible = prop.data.visible ? 1 : 0;
    } else if (prop.id == PROP_COLORMAP) {
      SDL_free (prop.data.colormap.cmap);
    }
  } while (prop.id != PROP_END);

  l->hierarchy_file_offset = read_offset (src, h);
  l->layer_mask_offset     = read_offset (src, h);

  return l;
}

static void free_xcf_channel (xcf_channel * c) {
  SDL_free (c->name);
  SDL_free (c);
}

static xcf_channel * read_xcf_channel (SDL_RWops * src, const xcf_header * h) {
  xcf_channel * l;
  xcf_prop    prop;

  l = (xcf_channel *) SDL_malloc (sizeof (xcf_channel));
  l->width  = SDL_ReadBE32 (src);
  l->height = SDL_ReadBE32 (src);

  l->name = read_string (src);
#ifdef DEBUG
  printf ("channel (%u,%u) '%s'\n", l->width, l->height, l->name);
#endif

  l->selection = 0;
  do {
    if (!xcf_read_property (src, &prop)) {
      free_xcf_channel (l);
      return NULL;
    }
    switch (prop.id) {
    case PROP_OPACITY:
      l->opacity = prop.data.opacity << 24;
      break;
    case PROP_COLOR:
      l->color = ((Uint32) prop.data.color[0] << 16)
    | ((Uint32) prop.data.color[1] << 8)
    | ((Uint32) prop.data.color[2]);
      break;
    case PROP_SELECTION:
      l->selection = 1;
      break;
    case PROP_VISIBLE:
      l->visible = prop.data.visible ? 1 : 0;
      break;
    default:
        ;
    }
  } while (prop.id != PROP_END);

  l->hierarchy_file_offset = read_offset (src, h);

  return l;
}

static void free_xcf_hierarchy (xcf_hierarchy * h) {
  SDL_free (h->level_file_offsets);
  SDL_free (h);
}

static xcf_hierarchy * read_xcf_hierarchy (SDL_RWops * src, const xcf_header * head) {
  xcf_hierarchy * h;
  int i;

  h = (xcf_hierarchy *) SDL_malloc (sizeof (xcf_hierarchy));
  h->width  = SDL_ReadBE32 (src);
  h->height = SDL_ReadBE32 (src);
  h->bpp    = SDL_ReadBE32 (src);

  h->level_file_offsets = NULL;
  i = 0;
  do {
    h->level_file_offsets = (Uint32 *) SDL_realloc (h->level_file_offsets, sizeof (Uint32) * (i+1));
    h->level_file_offsets [i] = read_offset (src, head);
  } while (h->level_file_offsets [i++]);

  return h;
}

static void free_xcf_level (xcf_level * l) {
  SDL_free (l->tile_file_offsets);
  SDL_free (l);
}

static xcf_level * read_xcf_level (SDL_RWops * src, const xcf_header * h) {
  xcf_level * l;
  int i;

  l = (xcf_level *) SDL_malloc (sizeof (xcf_level));
  l->width  = SDL_ReadBE32 (src);
  l->height = SDL_ReadBE32 (src);

  l->tile_file_offsets = NULL;
  i = 0;
  do {
    l->tile_file_offsets = (Uint32 *) SDL_realloc (l->tile_file_offsets, sizeof (Uint32) * (i+1));
    l->tile_file_offsets [i] = read_offset (src, h);
  } while (l->tile_file_offsets [i++]);

  return l;
}

static void free_xcf_tile (unsigned char * t) {
  SDL_free (t);
}

static unsigned char * load_xcf_tile_none (SDL_RWops * src, Uint32 len, int bpp, int x, int y) {
  unsigned char * load;

  load = (unsigned char *) SDL_malloc (len); // expect this is okay
  if (load != NULL)
    SDL_RWread (src, load, len, 1);

  return load;
}

static unsigned char * load_xcf_tile_rle (SDL_RWops * src, Uint32 len, int bpp, int x, int y) {
  unsigned char * load, * t, * data, * d;
  Uint32 reallen;
  int i, size, count, j, length;
  unsigned char val;

  if (len == 0) {  /* probably bogus data. */
    return NULL;
  }

  t = load = (unsigned char *) SDL_malloc (len);
  if (load == NULL)
    return NULL;
  reallen = SDL_RWread (src, t, 1, len);

  data = (unsigned char *) SDL_calloc (1, x*y*bpp);
  for (i = 0; i < bpp; i++) {
    d    = data + i;
    size = x*y;
    count = 0;

    while (size > 0) {
      val = *t++;

      length = val;
      if (length >= 128) {
        length = 255 - (length - 1);
        if (length == 128) {
          length = (*t << 8) + t[1];
          t += 2;
        }

        if (((size_t) (t - load) + length) >= len) {
          break;  /* bogus data */
        } else if (length > size) {
          break;  /* bogus data */
        }

        count += length;
        size -= length;

        while (length-- > 0) {
          *d = *t++;
          d += bpp;
        }
      } else {
        length += 1;
        if (length == 128) {
          length = (*t << 8) + t[1];
          t += 2;
        }

        if (((size_t) (t - load)) >= len) {
          break;  /* bogus data */
        } else if (length > size) {
          break;  /* bogus data */
        }

        count += length;
        size -= length;

        val = *t++;

        for (j = 0; j < length; j++) {
          *d = val;
          d += bpp;
        }
      }
    }

    if (size > 0) {
      break;  /* just drop out, untouched data initialized to zero. */
    }

  }

  SDL_free (load);
  return (data);
}

static Uint32 rgb2grey (Uint32 a) {
  Uint8 l;
  l = (Uint8)(0.2990 * ((a & 0x00FF0000) >> 16)
    + 0.5870 * ((a & 0x0000FF00) >>  8)
    + 0.1140 * ((a & 0x000000FF)));

  return (l << 16) | (l << 8) | l;
}

static void create_channel_surface (SDL_Surface * surf, xcf_image_type itype, Uint32 color, Uint32 opacity) {
  Uint32 c = 0;

  switch (itype) {
  case IMAGE_RGB:
  case IMAGE_INDEXED:
    c = opacity | color;
    break;
  case IMAGE_GREYSCALE:
    c = opacity | rgb2grey (color);
    break;
  }
  SDL_FillRect (surf, NULL, c);
}

static int 
do_layer_surface(SDL_Surface * surface, SDL_RWops * src, xcf_header * head, xcf_layer * layer, load_tile_type load_tile)
{
    xcf_hierarchy  *hierarchy;
    xcf_level      *level;
    unsigned char  *tile;
    Uint8          *p8;
    Uint16         *p16;
    Uint32         *p;
    int            i, j;
    Uint32         x, y, tx, ty, ox, oy;
    Uint32         *row;
    Uint32         length;

    SDL_RWseek(src, layer->hierarchy_file_offset, RW_SEEK_SET);
    hierarchy = read_xcf_hierarchy(src, head);

    if (hierarchy->bpp > 4) {  /* unsupported. */
        SDL_Log("Unknown Gimp image bpp (%u)\n", (unsigned int) hierarchy->bpp);
        free_xcf_hierarchy(hierarchy);
        return 1;
    }

    if ((hierarchy->width > 20000) || (hierarchy->height > 20000)) {  /* arbitrary limit to avoid integer overflow. */
        SDL_Log("Gimp image too large (%ux%u)\n", (unsigned int) hierarchy->width, (unsigned int) hierarchy->height);
        free_xcf_hierarchy(hierarchy);
        return 1;
    }

    level = NULL;
    for (i = 0; hierarchy->level_file_offsets[i]; i++) {
        if (SDL_RWseek(src, hierarchy->level_file_offsets[i], RW_SEEK_SET) < 0)
            break;
        if (i > 0) // skip level except the 1st one, just like GIMP does
            continue;
        level = read_xcf_level(src, head);

        ty = tx = 0;
        for (j = 0; level->tile_file_offsets[j]; j++) {
            SDL_RWseek(src, level->tile_file_offsets[j], RW_SEEK_SET);
            ox = tx + 64 > level->width ? level->width % 64 : 64;
            oy = ty + 64 > level->height ? level->height % 64 : 64;
            length = ox*oy*6;

            if (level->tile_file_offsets[j + 1] > level->tile_file_offsets[j]) {
                length = level->tile_file_offsets[j + 1] - level->tile_file_offsets[j];
            }
            tile = load_tile(src, length, hierarchy->bpp, ox, oy);

            if (!tile) {
                if (hierarchy) {
                    free_xcf_hierarchy(hierarchy);
                }
                if (level) {
                    free_xcf_level(level);
                }
                return 1;
            }

            p8 = tile;
            p16 = (Uint16 *) p8;
            p = (Uint32 *) p8;
            for (y = ty; y < ty + oy; y++) {
                if ((y >= surface->h) || ((tx+ox) > surface->w)) {
                    break;
                }
                row = (Uint32 *) ((Uint8 *) surface->pixels + y * surface->pitch + tx * 4);
                switch (hierarchy->bpp) {
                case 4:
                    for (x = tx; x < tx + ox; x++)
                        *row++ = Swap32(*p++);
                    break;
                case 3:
                    for (x = tx; x < tx + ox; x++) {
                        *row = 0xFF000000;
                        *row |= ((Uint32)*p8++ << 16);
                        *row |= ((Uint32)*p8++ << 8);
                        *row |= ((Uint32)*p8++ << 0);
                        row++;
                    }
                    break;
                case 2:
                    /* Indexed / Greyscale + Alpha */
                    switch (head->image_type) {
                    case IMAGE_INDEXED:
                        for (x = tx; x < tx + ox; x++) {
                            *row = ((Uint32)(head->cm_map[*p8 * 3]) << 16);
                            *row |= ((Uint32)(head->cm_map[*p8 * 3 + 1]) << 8);
                            *row |= ((Uint32)(head->cm_map[*p8++ * 3 + 2]) << 0);
                            *row |= ((Uint32)*p8++ << 24);
                            row++;
                        }
                        break;
                    case IMAGE_GREYSCALE:
                        for (x = tx; x < tx + ox; x++) {
                            *row = ((Uint32)*p8 << 16);
                            *row |= ((Uint32)*p8 << 8);
                            *row |= ((Uint32)*p8++ << 0);
                            *row |= ((Uint32)*p8++ << 24);
                            row++;
                        }
                        break;
                    default:
                        SDL_Log("Unknown Gimp image type (%d)\n", head->image_type);
                        if (hierarchy) {
                            free_xcf_hierarchy(hierarchy);
                        }
                        if (level)
                            free_xcf_level(level);
                        return 1;
                    }
                    break;
                case 1:
                    /* Indexed / Greyscale */
                    switch (head->image_type) {
                    case IMAGE_INDEXED:
                        for (x = tx; x < tx + ox; x++) {
                            *row++ = 0xFF000000
                                | ((Uint32)(head->cm_map[*p8 * 3]) << 16)
                                | ((Uint32)(head->cm_map[*p8 * 3 + 1]) << 8)
                                | ((Uint32)(head->cm_map[*p8 * 3 + 2]) << 0);
                            p8++;
                        }
                        break;
                    case IMAGE_GREYSCALE:
                        for (x = tx; x < tx + ox; x++) {
                            *row++ = 0xFF000000
                                | (((Uint32)(*p8)) << 16)
                                | (((Uint32)(*p8)) << 8)
                                | (((Uint32)(*p8)) << 0);
                            ++p8;
                        }
                        break;
                    default:
                        SDL_Log("Unknown Gimp image type (%d)\n", head->image_type);
                        if (tile)
                            free_xcf_tile(tile);
                        if (level)
                            free_xcf_level(level);
                        if (hierarchy)
                            free_xcf_hierarchy(hierarchy);
                        return 1;
                    }
                    break;
                }
            }
            free_xcf_tile(tile);

            tx += 64;
            if (tx >= level->width) {
                tx = 0;
                ty += 64;
            }
            if (ty >= level->height) {
                break;
            }
        }
        free_xcf_level(level);
    }

    free_xcf_hierarchy(hierarchy);

    return 0;
}

SDL_Surface *IMG_LoadXCF_RW(SDL_RWops *src)
{
  Sint64 start;
  const char *error = NULL;
  SDL_Surface *surface, *lays;
  xcf_header * head;
  xcf_layer  * layer;
  xcf_channel ** channel;
  int chnls, i, offsets;
  Sint64 offset, fp;

  unsigned char * (* load_tile) (SDL_RWops *, Uint32, int, int, int);

  if (!src) {
    /* The error message has been set in SDL_RWFromFile */
    return NULL;
  }
  start = SDL_RWtell(src);

  /* Initialize the data we will clean up when we're done */
  surface = NULL;

  head = read_xcf_header(src);
  if (!head) {
    return NULL;
  }

  switch (head->compr) {
  case COMPR_NONE:
    load_tile = load_xcf_tile_none;
    break;
  case COMPR_RLE:
    load_tile = load_xcf_tile_rle;
    break;
  default:
    SDL_Log("Unsupported Compression.\n");
    free_xcf_header (head);
    return NULL;
  }

  /* Create the surface of the appropriate type */
  surface = SDL_CreateRGBSurface(SDL_SWSURFACE, head->width, head->height, 32,
                 0x00FF0000,0x0000FF00,0x000000FF,0xFF000000);

  if ( surface == NULL ) {
    error = "Out of memory";
    goto done;
  }

  offsets = 0;

  while ((offset = read_offset (src, head))) {
    head->layer_file_offsets = (Uint32 *) SDL_realloc (head->layer_file_offsets, sizeof (Uint32) * (offsets+1));
    head->layer_file_offsets [offsets] = (Uint32)offset;
    offsets++;
  }
  fp = SDL_RWtell (src);

  lays = SDL_CreateRGBSurface(SDL_SWSURFACE, head->width, head->height, 32,
              0x00FF0000,0x0000FF00,0x000000FF,0xFF000000);

  if ( lays == NULL ) {
    error = "Out of memory";
    goto done;
  }

  // Blit layers backwards, because Gimp saves them highest first
  for (i = offsets; i > 0; i--) {
    SDL_Rect rs, rd;
    SDL_RWseek (src, head->layer_file_offsets [i-1], RW_SEEK_SET);

    layer = read_xcf_layer (src, head);
    if (layer != NULL) {
      do_layer_surface (lays, src, head, layer, load_tile);
      rs.x = 0;
      rs.y = 0;
      rs.w = layer->width;
      rs.h = layer->height;
      rd.x = layer->offset_x;
      rd.y = layer->offset_y;
      rd.w = layer->width;
      rd.h = layer->height;

      if (layer->visible)
        SDL_BlitSurface (lays, &rs, surface, &rd);
      free_xcf_layer (layer);
    }
  }

  SDL_FreeSurface (lays);

  SDL_RWseek (src, fp, RW_SEEK_SET);

  // read channels
  channel = NULL;
  chnls   = 0;
  while ((offset = read_offset (src, head))) {
    channel = (xcf_channel **) SDL_realloc (channel, sizeof (xcf_channel *) * (chnls+1));
    fp = SDL_RWtell (src);
    SDL_RWseek (src, offset, RW_SEEK_SET);
    channel [chnls] = (read_xcf_channel (src, head));
    if (channel [chnls] != NULL)
      chnls++;
    SDL_RWseek (src, fp, RW_SEEK_SET);
  }

  if (chnls) {
    SDL_Surface * chs;

    chs = SDL_CreateRGBSurface(SDL_SWSURFACE, head->width, head->height, 32,
               0x00FF0000,0x0000FF00,0x000000FF,0xFF000000);

    if (chs == NULL) {
      error = "Out of memory";
      goto done;
    }
    for (i = 0; i < chnls; i++) {
      //      printf ("CNLBLT %i\n", i);
      if (!channel [i]->selection && channel [i]->visible) {
    create_channel_surface (chs, (xcf_image_type)head->image_type, channel [i]->color, channel [i]->opacity);
    SDL_BlitSurface (chs, NULL, surface, NULL);
      }
      free_xcf_channel (channel [i]);
    }
    SDL_free(channel);

    SDL_FreeSurface (chs);
  }

done:
  free_xcf_header (head);
  if ( error ) {
    SDL_RWseek(src, start, RW_SEEK_SET);
    if ( surface ) {
      SDL_FreeSurface(surface);
      surface = NULL;
    }
    IMG_SetError("%s", error);
  }

  return(surface);
}

#else
#if _MSC_VER >= 1300
#pragma warning(disable : 4100) /* warning C4100: 'op' : unreferenced formal parameter */
#endif

/* See if an image is contained in a data source */
int IMG_isXCF(SDL_RWops *src)
{
  return(0);
}

/* Load a XCF type image from an SDL datasource */
SDL_Surface *IMG_LoadXCF_RW(SDL_RWops *src)
{
  return(NULL);
}

#endif /* LOAD_XCF */