img_png.c

It is extension program for SDL to display images other than bmp, but all the other formats.

#endif /* LOAD_PNG_DYNAMIC */

/* See if an image is contained in a data source */
int IMG_isPNG(SDL_RWops *src)
{
	int start;
	int is_PNG;
	Uint8 magic[4];

	if ( !src )
		return 0;
	start = SDL_RWtell(src);
	is_PNG = 0;
	if ( SDL_RWread(src, magic, 1, sizeof(magic)) == sizeof(magic) ) {
                if ( magic[0] == 0x89 &&
                     magic[1] == 'P' &&
                     magic[2] == 'N' &&
                     magic[3] == 'G' ) {
			is_PNG = 1;
		}
	}
	SDL_RWseek(src, start, SEEK_SET);
	return(is_PNG);
}

/* Load a PNG type image from an SDL datasource */
static void png_read_data(png_structp ctx, png_bytep area, png_size_t size)
{
	SDL_RWops *src;

	src = (SDL_RWops *)lib.png_get_io_ptr(ctx);
	SDL_RWread(src, area, size, 1);
}
SDL_Surface *IMG_LoadPNG_RW(SDL_RWops *src)
{
	int start;
	const char *error;
	SDL_Surface *volatile surface;
	png_structp png_ptr;
	png_infop info_ptr;
	png_uint_32 width, height;
	int bit_depth, color_type, interlace_type;
	Uint32 Rmask;
	Uint32 Gmask;
	Uint32 Bmask;
	Uint32 Amask;
	SDL_Palette *palette;
	png_bytep *volatile row_pointers;
	int row, i;
	volatile int ckey = -1;
	png_color_16 *transv;

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

	if ( IMG_InitPNG() < 0 ) {
		return NULL;
	}

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

	/* Create the PNG loading context structure */
	png_ptr = lib.png_create_read_struct(PNG_LIBPNG_VER_STRING,
					  NULL,NULL,NULL);
	if (png_ptr == NULL){
		error = "Couldn't allocate memory for PNG file or incompatible PNG dll";
		goto done;
	}

	 /* Allocate/initialize the memory for image information.  REQUIRED. */
	info_ptr = lib.png_create_info_struct(png_ptr);
	if (info_ptr == NULL) {
		error = "Couldn't create image information for PNG file";
		goto done;
	}

	/* Set error handling if you are using setjmp/longjmp method (this is
	 * the normal method of doing things with libpng).  REQUIRED unless you
	 * set up your own error handlers in png_create_read_struct() earlier.
	 */
	if ( setjmp(png_ptr->jmpbuf) ) {
		error = "Error reading the PNG file.";
		goto done;
	}

	/* Set up the input control */
	lib.png_set_read_fn(png_ptr, src, png_read_data);

	/* Read PNG header info */
	lib.png_read_info(png_ptr, info_ptr);
	lib.png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth,
			&color_type, &interlace_type, NULL, NULL);

	/* tell libpng to strip 16 bit/color files down to 8 bits/color */
	lib.png_set_strip_16(png_ptr) ;

	/* Extract multiple pixels with bit depths of 1, 2, and 4 from a single
	 * byte into separate bytes (useful for paletted and grayscale images).
	 */
	lib.png_set_packing(png_ptr);

	/* scale greyscale values to the range 0..255 */
	if(color_type == PNG_COLOR_TYPE_GRAY)
		lib.png_set_expand(png_ptr);

	/* For images with a single "transparent colour", set colour key;
	   if more than one index has transparency, or if partially transparent
	   entries exist, use full alpha channel */
	if (lib.png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS)) {
	        int num_trans;
		Uint8 *trans;
		lib.png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans,
			     &transv);
		if(color_type == PNG_COLOR_TYPE_PALETTE) {
		    /* Check if all tRNS entries are opaque except one */
		    int i, t = -1;
		    for(i = 0; i < num_trans; i++)
			if(trans[i] == 0) {
			    if(t >= 0)
				break;
			    t = i;
			} else if(trans[i] != 255)
			    break;
		    if(i == num_trans) {
			/* exactly one transparent index */
			ckey = t;
		    } else {
			/* more than one transparent index, or translucency */
			lib.png_set_expand(png_ptr);
		    }
		} else
		    ckey = 0; /* actual value will be set later */
	}

	if ( color_type == PNG_COLOR_TYPE_GRAY_ALPHA )
		lib.png_set_gray_to_rgb(png_ptr);

	lib.png_read_update_info(png_ptr, info_ptr);

	lib.png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth,
			&color_type, &interlace_type, NULL, NULL);

	/* Allocate the SDL surface to hold the image */
	Rmask = Gmask = Bmask = Amask = 0 ; 
	if ( color_type != PNG_COLOR_TYPE_PALETTE ) {
		if ( SDL_BYTEORDER == SDL_LIL_ENDIAN ) {
			Rmask = 0x000000FF;
			Gmask = 0x0000FF00;
			Bmask = 0x00FF0000;
			Amask = (info_ptr->channels == 4) ? 0xFF000000 : 0;
		} else {
		        int s = (info_ptr->channels == 4) ? 0 : 8;
			Rmask = 0xFF000000 >> s;
			Gmask = 0x00FF0000 >> s;
			Bmask = 0x0000FF00 >> s;
			Amask = 0x000000FF >> s;
		}
	}
	surface = SDL_AllocSurface(SDL_SWSURFACE, width, height,
			bit_depth*info_ptr->channels, Rmask,Gmask,Bmask,Amask);
	if ( surface == NULL ) {
		error = "Out of memory";
		goto done;
	}

	if(ckey != -1) {
	        if(color_type != PNG_COLOR_TYPE_PALETTE)
			/* FIXME: Should these be truncated or shifted down? */
		        ckey = SDL_MapRGB(surface->format,
			                 (Uint8)transv->red,
			                 (Uint8)transv->green,
			                 (Uint8)transv->blue);
	        SDL_SetColorKey(surface, SDL_SRCCOLORKEY, ckey);
	}

	/* Create the array of pointers to image data */
	row_pointers = (png_bytep*) malloc(sizeof(png_bytep)*height);
	if ( (row_pointers == NULL) ) {
		error = "Out of memory";
		goto done;
	}
	for (row = 0; row < (int)height; row++) {
		row_pointers[row] = (png_bytep)
				(Uint8 *)surface->pixels + row*surface->pitch;
	}

	/* Read the entire image in one go */
	lib.png_read_image(png_ptr, row_pointers);

	/* and we're done!  (png_read_end() can be omitted if no processing of
	 * post-IDAT text/time/etc. is desired)
	 * In some cases it can't read PNG's created by some popular programs (ACDSEE),
	 * we do not want to process comments, so we omit png_read_end

	lib.png_read_end(png_ptr, info_ptr);
	*/

	/* Load the palette, if any */
	palette = surface->format->palette;
	if ( palette ) {
	    if(color_type == PNG_COLOR_TYPE_GRAY) {
		palette->ncolors = 256;
		for(i = 0; i < 256; i++) {
		    palette->colors[i].r = i;
		    palette->colors[i].g = i;
		    palette->colors[i].b = i;
		}
	    } else if (info_ptr->num_palette > 0 ) {
		palette->ncolors = info_ptr->num_palette; 
		for( i=0; i<info_ptr->num_palette; ++i ) {
		    palette->colors[i].b = info_ptr->palette[i].blue;
		    palette->colors[i].g = info_ptr->palette[i].green;
		    palette->colors[i].r = info_ptr->palette[i].red;
		}
	    }
	}

done:	/* Clean up and return */
	if ( png_ptr ) {
		lib.png_destroy_read_struct(&png_ptr,
		                        info_ptr ? &info_ptr : (png_infopp)0,
								(png_infopp)0);
	}
	if ( row_pointers ) {
		free(row_pointers);
	}
	if ( error ) {
		SDL_RWseek(src, start, SEEK_SET);
		if ( surface ) {
			SDL_FreeSurface(surface);
			surface = NULL;
		}
		IMG_QuitPNG();
		IMG_SetError(error);
	} else {
		IMG_QuitPNG();
	}
	return(surface); 
}

#else

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

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

#endif /* LOAD_PNG */