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img.c

/*
    IMGLIB:  An example image loading library for use with SDL
    Copyright (C) 1999  Sam Lantinga

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
    License as published by the Free Software Foundation; either
    version 2 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
    Library General Public License for more details.

    You should have received a copy of the GNU Library General Public
    License along with this library; if not, write to the Free
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

    Sam Lantinga
    5635-34 Springhouse Dr.
    Pleasanton, CA 94588 (USA)
    slouken@devolution.com
*/

/* A simple library to load images of various formats as SDL surfaces */

#include <stdio.h>
#include <string.h>
#include <ctype.h>

#include "IMG.h"

/* Table of image detection and loading functions */
static struct {
      char *type;
      int (*is)(SDL_RWops *src);
      SDL_Surface *(*load)(SDL_RWops *src);
} supported[] = {
        /* keep magicless formats first (denoted by is==NULL) */
      { "PNG", IMG_isPNG, IMG_LoadPNG_RW },
};

/* Load an image from a file */
SDL_Surface *IMG_Load(const char *file)
{
    SDL_RWops *src = SDL_RWFromFile(file, "rb");
    char *ext = strrchr(file, '.');
    if(ext)
      ext++;
    return IMG_LoadTyped_RW(src, 1, ext);
}

/* Load an image from an SDL datasource (for compatibility) */
SDL_Surface *IMG_Load_RW(SDL_RWops *src, int freesrc)
{
    return IMG_LoadTyped_RW(src, freesrc, NULL);
}

/* Portable case-insensitive string compare function */
static int string_equals(const char *str1, const char *str2)
{
      while ( *str1 && *str2 ) {
            if ( toupper((unsigned char)*str1) !=
                 toupper((unsigned char)*str2) )
                  break;
            ++str1;
            ++str2;
      }
      return (!*str1 && !*str2);
}

/* Load an image from an SDL datasource, optionally specifying the type */
SDL_Surface *IMG_LoadTyped_RW(SDL_RWops *src, int freesrc, char *type)
{
      int i, start;
      SDL_Surface *image;

      /* Make sure there is something to do.. */
      if ( src == NULL ) {
            return(NULL);
      }

      /* See whether or not this data source can handle seeking */
      if ( SDL_RWseek(src, 0, SEEK_CUR) < 0 ) {
            IMG_SetError("Can't seek in this data source");
            return(NULL);
      }

      /* Detect the type of image being loaded */
      start = SDL_RWtell(src);
      image = NULL;
      for ( i=0; supported[i].type && !image; ++i ) {
              if( (supported[i].is
                 && (SDL_RWseek(src, start, SEEK_SET),
                   supported[i].is(src)))
                || (type && string_equals(type, supported[i].type))) {
#ifdef DEBUG_IMGLIB
                  fprintf(stderr, "IMGLIB: Loading image as %s\n",
                                          supported[i].type);
#endif
                  SDL_RWseek(src, start, SEEK_SET);
                  image = supported[i].load(src);
                  break;
            }
      }

      /* Clean up, check for errors, and return */
      if ( freesrc ) {
            SDL_RWclose(src);
      }
      if ( image == NULL ) {
            IMG_SetError("Unsupported image format");
      }
      return(image);
}

/* Invert the alpha of a surface for use with OpenGL
   This function is a no-op and only kept for backwards compatibility.
 */
int IMG_InvertAlpha(int on)
{
    return 1;
}

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