IMG_jpg.c
author Sam Lantinga <slouken@libsdl.org>
Sat, 29 Dec 2001 01:55:32 +0000
changeset 61 a8a23146b406
parent 53 96b084473b47
child 71 e2eb6980be07
permissions -rw-r--r--
*** empty log message ***
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/*
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    SDL_image:  An example image loading library for use with SDL
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    Copyright (C) 1999, 2000, 2001  Sam Lantinga
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    This library is free software; you can redistribute it and/or
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    modify it under the terms of the GNU Library General Public
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    License as published by the Free Software Foundation; either
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    version 2 of the License, or (at your option) any later version.
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    This library is distributed in the hope that it will be useful,
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    but WITHOUT ANY WARRANTY; without even the implied warranty of
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    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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    Library General Public License for more details.
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    You should have received a copy of the GNU Library General Public
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    License along with this library; if not, write to the Free
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    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
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    Sam Lantinga
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    slouken@libsdl.org
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*/
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/* $Id$ */
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/* This is a JPEG image file loading framework */
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#include <stdio.h>
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#include <string.h>
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#include <setjmp.h>
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#include "SDL_image.h"
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#ifdef LOAD_JPG
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#include <jpeglib.h>
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/* Define this for fast loading and not as good image quality */
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/*#define FAST_JPEG*/
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/* See if an image is contained in a data source */
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int IMG_isJPG(SDL_RWops *src)
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{
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	int is_JPG;
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	Uint8 magic[4];
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	is_JPG = 0;
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	if ( SDL_RWread(src, magic, 2, 1) ) {
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		if ( (magic[0] == 0xFF) && (magic[1] == 0xD8) ) {
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			SDL_RWread(src, magic, 4, 1);
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			SDL_RWread(src, magic, 4, 1);
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			if ( memcmp((char *)magic, "JFIF", 4) == 0 ) {
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				is_JPG = 1;
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			}
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		}
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	}
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	return(is_JPG);
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}
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#define INPUT_BUFFER_SIZE	4096
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typedef struct {
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	struct jpeg_source_mgr pub;
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	SDL_RWops *ctx;
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	Uint8 buffer[INPUT_BUFFER_SIZE];
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} my_source_mgr;
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/*
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 * Initialize source --- called by jpeg_read_header
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 * before any data is actually read.
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 */
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static void init_source (j_decompress_ptr cinfo)
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{
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	/* We don't actually need to do anything */
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	return;
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}
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/*
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 * Fill the input buffer --- called whenever buffer is emptied.
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 */
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static int fill_input_buffer (j_decompress_ptr cinfo)
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{
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	my_source_mgr * src = (my_source_mgr *) cinfo->src;
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	int nbytes;
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	nbytes = SDL_RWread(src->ctx, src->buffer, 1, INPUT_BUFFER_SIZE);
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	if (nbytes <= 0) {
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		/* Insert a fake EOI marker */
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		src->buffer[0] = (Uint8) 0xFF;
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		src->buffer[1] = (Uint8) JPEG_EOI;
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		nbytes = 2;
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	}
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	src->pub.next_input_byte = src->buffer;
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	src->pub.bytes_in_buffer = nbytes;
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	return TRUE;
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}
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/*
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 * Skip data --- used to skip over a potentially large amount of
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 * uninteresting data (such as an APPn marker).
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 *
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 * Writers of suspendable-input applications must note that skip_input_data
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 * is not granted the right to give a suspension return.  If the skip extends
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 * beyond the data currently in the buffer, the buffer can be marked empty so
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 * that the next read will cause a fill_input_buffer call that can suspend.
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 * Arranging for additional bytes to be discarded before reloading the input
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 * buffer is the application writer's problem.
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 */
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static void skip_input_data (j_decompress_ptr cinfo, long num_bytes)
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{
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	my_source_mgr * src = (my_source_mgr *) cinfo->src;
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	/* Just a dumb implementation for now.	Could use fseek() except
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	 * it doesn't work on pipes.  Not clear that being smart is worth
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	 * any trouble anyway --- large skips are infrequent.
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	 */
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	if (num_bytes > 0) {
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		while (num_bytes > (long) src->pub.bytes_in_buffer) {
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			num_bytes -= (long) src->pub.bytes_in_buffer;
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			(void) src->pub.fill_input_buffer(cinfo);
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			/* note we assume that fill_input_buffer will never
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			 * return FALSE, so suspension need not be handled.
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			 */
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		}
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		src->pub.next_input_byte += (size_t) num_bytes;
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		src->pub.bytes_in_buffer -= (size_t) num_bytes;
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	}
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}
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/*
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 * Terminate source --- called by jpeg_finish_decompress
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 * after all data has been read.
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 */
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static void term_source (j_decompress_ptr cinfo)
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{
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	/* We don't actually need to do anything */
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	return;
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}
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/*
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 * Prepare for input from a stdio stream.
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 * The caller must have already opened the stream, and is responsible
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 * for closing it after finishing decompression.
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 */
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static void jpeg_SDL_RW_src (j_decompress_ptr cinfo, SDL_RWops *ctx)
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{
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  my_source_mgr *src;
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  /* The source object and input buffer are made permanent so that a series
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   * of JPEG images can be read from the same file by calling jpeg_stdio_src
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   * only before the first one.  (If we discarded the buffer at the end of
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   * one image, we'd likely lose the start of the next one.)
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   * This makes it unsafe to use this manager and a different source
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   * manager serially with the same JPEG object.  Caveat programmer.
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   */
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  if (cinfo->src == NULL) {	/* first time for this JPEG object? */
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    cinfo->src = (struct jpeg_source_mgr *)
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      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
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				  sizeof(my_source_mgr));
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    src = (my_source_mgr *) cinfo->src;
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  }
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  src = (my_source_mgr *) cinfo->src;
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  src->pub.init_source = init_source;
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  src->pub.fill_input_buffer = fill_input_buffer;
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  src->pub.skip_input_data = skip_input_data;
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  src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
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  src->pub.term_source = term_source;
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  src->ctx = ctx;
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  src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
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  src->pub.next_input_byte = NULL; /* until buffer loaded */
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}
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struct my_error_mgr {
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	struct jpeg_error_mgr errmgr;
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	jmp_buf escape;
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};
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static void my_error_exit(j_common_ptr cinfo)
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{
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	struct my_error_mgr *err = (struct my_error_mgr *)cinfo->err;
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	longjmp(err->escape, 1);
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}
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static void output_no_message(j_common_ptr cinfo)
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{
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	/* do nothing */
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}
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/* Load a JPEG type image from an SDL datasource */
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SDL_Surface *IMG_LoadJPG_RW(SDL_RWops *src)
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{
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	struct jpeg_decompress_struct cinfo;
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	JSAMPROW rowptr[1];
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	SDL_Surface *volatile surface = NULL;
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	struct my_error_mgr jerr;
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	/* Create a decompression structure and load the JPEG header */
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	cinfo.err = jpeg_std_error(&jerr.errmgr);
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	jerr.errmgr.error_exit = my_error_exit;
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	jerr.errmgr.output_message = output_no_message;
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	if(setjmp(jerr.escape)) {
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		/* If we get here, libjpeg found an error */
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		jpeg_destroy_decompress(&cinfo);
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		IMG_SetError("JPEG loading error");
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		SDL_FreeSurface(surface);
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		return NULL;
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	}
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	jpeg_create_decompress(&cinfo);
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	jpeg_SDL_RW_src(&cinfo, src);
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	jpeg_read_header(&cinfo, TRUE);
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	/* Set 24-bit RGB output */
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	cinfo.out_color_space = JCS_RGB;
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	cinfo.quantize_colors = FALSE;
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#ifdef FAST_JPEG
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	cinfo.scale_num   = 1;
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	cinfo.scale_denom = 1;
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	cinfo.dct_method = JDCT_FASTEST;
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	cinfo.do_fancy_upsampling = FALSE;
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#endif
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	jpeg_calc_output_dimensions(&cinfo);
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	/* Allocate an output surface to hold the image */
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	surface = SDL_AllocSurface(SDL_SWSURFACE,
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	               cinfo.output_width, cinfo.output_height, 24,
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#if SDL_BYTEORDER == SDL_LIL_ENDIAN
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	                           0x0000FF, 0x00FF00, 0xFF0000,
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#else
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	                           0xFF0000, 0x00FF00, 0x0000FF,
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#endif
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				   0);
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	if ( surface == NULL ) {
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		IMG_SetError("Out of memory");
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		goto done;
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	}
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	/* Decompress the image */
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	jpeg_start_decompress(&cinfo);
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	while ( cinfo.output_scanline < cinfo.output_height ) {
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		rowptr[0] = (JSAMPROW)(Uint8 *)surface->pixels +
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		                    cinfo.output_scanline * surface->pitch;
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		jpeg_read_scanlines(&cinfo, rowptr, (JDIMENSION) 1);
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	}
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	jpeg_finish_decompress(&cinfo);
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	/* Clean up and return */
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done:
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	jpeg_destroy_decompress(&cinfo);
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	return(surface);
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}
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#else
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/* See if an image is contained in a data source */
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int IMG_isJPG(SDL_RWops *src)
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{
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	return(0);
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}
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/* Load a JPEG type image from an SDL datasource */
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SDL_Surface *IMG_LoadJPG_RW(SDL_RWops *src)
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{
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	return(NULL);
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}
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#endif /* LOAD_JPG */