img_pnm.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_pnm.c,v 1.2 2001/12/14 13:02:16 slouken Exp $ */

/*
 * PNM (portable anymap) image loader:
 *
 * Supports: PBM, PGM and PPM, ASCII and binary formats
 * (PBM and PGM are loaded as 8bpp surfaces)
 * Does not support: maximum component value > 255
 */

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

#include "SDL_image.h"

#ifdef LOAD_PNM

/* See if an image is contained in a data source */
int IMG_isPNM(SDL_RWops *src)
{
	char magic[2];

	/*
	 * PNM magic signatures:
	 * P1	PBM, ascii format
	 * P2	PGM, ascii format
	 * P3	PPM, ascii format
	 * P4	PBM, binary format
	 * P5	PGM, binary format
	 * P6	PPM, binary format
	 */
	return (SDL_RWread(src, magic, 2, 1)
		&& magic[0] == 'P' && magic[1] >= '1' && magic[1] <= '6');
}

/* read a non-negative integer from the source. return -1 upon error */
static int ReadNumber(SDL_RWops *src)
{
	int number;
	unsigned char ch;

	/* Initialize return value */
	number = 0;

	/* Skip leading whitespace */
	do {
		if ( ! SDL_RWread(src, &ch, 1, 1) ) {
			return(0);
		}
		/* Eat comments as whitespace */
		if ( ch == '#' ) {  /* Comment is '#' to end of line */
			do {
				if ( ! SDL_RWread(src, &ch, 1, 1) ) {
					return -1;
				}
			} while ( (ch != '\r') && (ch != '\n') );
		}
	} while ( isspace(ch) );

	/* Add up the number */
	do {
		number *= 10;
		number += ch-'0';

		if ( !SDL_RWread(src, &ch, 1, 1) ) {
			return -1;
		}
	} while ( isdigit(ch) );

	return(number);
}

SDL_Surface *IMG_LoadPNM_RW(SDL_RWops *src)
{
	SDL_Surface *surface = NULL;
	int width, height;
	int maxval, y, bpl;
	Uint8 *row;
	Uint8 *buf = NULL;
	char *error = NULL;
	Uint8 magic[2];
	int ascii;
	enum { PBM, PGM, PPM } kind;

#define ERROR(s) do { error = (s); goto done; } while(0)

	if(!src)
		return NULL;

	SDL_RWread(src, magic, 2, 1);
	kind = magic[1] - '1';
	ascii = 1;
	if(kind >= 3) {
		ascii = 0;
		kind -= 3;
	}

	width = ReadNumber(src);
	height = ReadNumber(src);
	if(width <= 0 || height <= 0)
		ERROR("Unable to read image width and height");

	if(kind != PBM) {
		maxval = ReadNumber(src);
		if(maxval <= 0 || maxval > 255)
			ERROR("unsupported PNM format");
	} else
		maxval = 255;	/* never scale PBMs */

	/* binary PNM allows just a single character of whitespace after
	   the last parameter, and we've already consumed it */

	if(kind == PPM) {
		/* 24-bit surface in R,G,B byte order */
		surface = SDL_AllocSurface(SDL_SWSURFACE, width, height, 24,
#if SDL_BYTEORDER == SDL_LIL_ENDIAN
					   0x000000ff, 0x0000ff00, 0x00ff0000,
#else
					   0x00ff0000, 0x0000ff00, 0x000000ff,
#endif
					   0);
	} else {
		/* load PBM/PGM as 8-bit indexed images */
		surface = SDL_AllocSurface(SDL_SWSURFACE, width, height, 8,
					   0, 0, 0, 0);
	}
	if ( surface == NULL )
		ERROR("Out of memory");
	bpl = width * surface->format->BytesPerPixel;
	if(kind == PGM) {
		SDL_Color *c = surface->format->palette->colors;
		int i;
		for(i = 0; i < 256; i++)
			c[i].r = c[i].g = c[i].b = i;
		surface->format->palette->ncolors = 256;
	} else if(kind == PBM) {
		/* for some reason PBM has 1=black, 0=white */
		SDL_Color *c = surface->format->palette->colors;
		c[0].r = c[0].g = c[0].b = 255;
		c[1].r = c[1].g = c[1].b = 0;
		surface->format->palette->ncolors = 2;
		bpl = (width + 7) >> 3;
		buf = malloc(bpl);
		if(buf == NULL)
			ERROR("Out of memory");
	}

	/* Read the image into the surface */
	row = surface->pixels;
	for(y = 0; y < height; y++) {
		if(ascii) {
			int i;
			if(kind == PBM) {
				for(i = 0; i < width; i++) {
					Uint8 ch;
					do {
						if(!SDL_RWread(src, &ch,
							       1, 1))
						       ERROR("file truncated");
						ch -= '0';
					} while(ch > 1);
					row[i] = ch;
				}
			} else {
				for(i = 0; i < bpl; i++) {
					int c;
					c = ReadNumber(src);
					if(c < 0)
						ERROR("file truncated");
					row[i] = c;
				}
			}
		} else {
			Uint8 *dst = (kind == PBM) ? buf : row;
			if(!SDL_RWread(src, dst, bpl, 1))
				ERROR("file truncated");
			if(kind == PBM) {
				/* expand bitmap to 8bpp */
				int i;
				for(i = 0; i < width; i++) {
					int bit = 7 - (i & 7);
					row[i] = (buf[i >> 3] >> bit) & 1;
				}
			}
		}
		if(maxval < 255) {
			/* scale up to full dynamic range (slow) */
			int i;
			for(i = 0; i < bpl; i++)
				row[i] = row[i] * 255 / maxval;
		}
		row += surface->pitch;
	}
done:
	free(buf);
	if(error) {
		SDL_FreeSurface(surface);
		IMG_SetError(error);
		surface = NULL;
	}
	return(surface);
}

#else

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

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

#endif /* LOAD_PNM */