img_png.c

sdl的image开发包

/*
    SDL_image:  An example image loading library for use with SDL
    Copyright (C) 1999, 2000, 2001  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
    [e-mail]
*/

/* $Id: IMG_png.c,v 1.7 2001/12/14 13:02:16 slouken Exp $ */

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

#include <stdlib.h>
#include <stdio.h>

#include "SDL_image.h"

#ifdef LOAD_PNG

/*=============================================================================
        File: SDL_png.c
     Purpose: A PNG loader and saver for the SDL library      
    Revision: 
  Created by: Philippe Lavoie          (2 November 1998)
              [e-mail]
 Modified by: 

 Copyright notice:
          Copyright (C) 1998 Philippe Lavoie
 
          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
          Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

    Comments: The load and save routine are basically the ones you can find
             in the example.c file from the libpng distribution.

  Changes:
    5/17/99 - Modified to use the new SDL data sources - Sam Lantinga

=============================================================================*/

#include "SDL_endian.h"

#ifdef macintosh
#define MACOS
#endif
#include <png.h>

#define PNG_BYTES_TO_CHECK 4

/* See if an image is contained in a data source */
int IMG_isPNG(SDL_RWops *src)
{
   unsigned char buf[PNG_BYTES_TO_CHECK];

   /* Read in the signature bytes */
   if (SDL_RWread(src, buf, 1, PNG_BYTES_TO_CHECK) != PNG_BYTES_TO_CHECK)
      return 0;

   /* Compare the first PNG_BYTES_TO_CHECK bytes of the signature. */
   return( !png_sig_cmp(buf, (png_size_t)0, PNG_BYTES_TO_CHECK));
}

/* 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 *)png_get_io_ptr(ctx);
	SDL_RWread(src, area, size, 1);
}
SDL_Surface *IMG_LoadPNG_RW(SDL_RWops *src)
{
	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;

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

	/* Check to make sure we have something to do */
	if ( ! src ) {
		goto done;
	}

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

	 /* Allocate/initialize the memory for image information.  REQUIRED. */
	info_ptr = png_create_info_struct(png_ptr);
	if (info_ptr == NULL) {
		IMG_SetError("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) ) {
		IMG_SetError("Error reading the PNG file.");
		goto done;
	}

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

	/* Read PNG header info */
	png_read_info(png_ptr, info_ptr);
	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 */
	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).
	 */
	png_set_packing(png_ptr);

	/* scale greyscale values to the range 0..255 */
	if(color_type == PNG_COLOR_TYPE_GRAY)
		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 (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS)) {
	        int num_trans;
		Uint8 *trans;
		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 */
			png_set_expand(png_ptr);
		    }
		} else
		    ckey = 0; /* actual value will be set later */
	}

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

	png_read_update_info(png_ptr, info_ptr);

	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 ) {
		IMG_SetError("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) ) {
		IMG_SetError("Out of memory");
		SDL_FreeSurface(surface);
		surface = NULL;
		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 */
	png_read_image(png_ptr, row_pointers);

	/* read rest of file, get additional chunks in info_ptr - REQUIRED */
	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 */
	png_destroy_read_struct(&png_ptr, info_ptr ? &info_ptr : (png_infopp)0,
								(png_infopp)0);
	if ( row_pointers ) {
		free(row_pointers);
	}
	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 */