jdatasrc.cpp

来自「Windows 图形编程 书籍」· C++ 代码 · 共 288 行

//-------------------------------------------------------------------------//
//          Windows Graphics Programming: Win32 GDI and DirectDraw         //
//                        ISBN  0-13-086985-6                              //
//                                                                         //
//  Modified by: Yuan, Feng                             www.fengyuan.com   //
//  Changes    : C++, exception, in-memory source, BGR byte order          //
//  Version    : 1.00.000, May 31, 2000                                    //
//-------------------------------------------------------------------------//

/*
 * jdatasrc.c
 *
 * Copyright (C) 1994-1996, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains decompression data source routines for the case of
 * reading JPEG data from a file (or any stdio stream).  While these routines
 * are sufficient for most applications, some will want to use a different
 * source manager.
 * IMPORTANT: we assume that fread() will correctly transcribe an array of
 * JOCTETs from 8-bit-wide elements on external storage.  If char is wider
 * than 8 bits on your machine, you may need to do some tweaking.
 */

/* this is not a core library module, so it doesn't define JPEG_INTERNALS */
#include "jinclude.h"
#include "jpeglib.h"
#include "jerror.h"

#define INPUT_BUF_SIZE  4096	/* choose an efficiently fread'able size */

// Expanded data source object for stdio input 
class my_source_mgr : public jpeg_source_mgr
{
	FILE *  infile;						/* source stream */
	JOCTET  buffer[INPUT_BUF_SIZE];
	boolean start_of_file;				/* have we gotten any data yet? */

public:

	void Reset(FILE * inf)
	{
		infile = inf;
		bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
		next_input_byte = NULL; /* until buffer loaded */
	}

	virtual void     init_source(j_decompress_ptr cinfo);
	virtual boolean  fill_input_buffer(j_decompress_ptr cinfo);
	virtual void     skip_input_data(j_decompress_ptr cinfo, long num_bytes);
	virtual void     term_source(j_decompress_ptr cinfo);

};



/*
 * Initialize source --- called by jpeg_read_header
 * before any data is actually read.
 */

void my_source_mgr::init_source(j_decompress_ptr cinfo)
{
	/* We reset the empty-input-file flag for each image,
	* but we don't clear the input buffer.
	* This is correct behavior for reading a series of images from one source.
	*/
	start_of_file = TRUE;
}


/*
 * Fill the input buffer --- called whenever buffer is emptied.
 *
 * In typical applications, this should read fresh data into the buffer
 * (ignoring the current state of next_input_byte & bytes_in_buffer),
 * reset the pointer & count to the start of the buffer, and return TRUE
 * indicating that the buffer has been reloaded.  It is not necessary to
 * fill the buffer entirely, only to obtain at least one more byte.
 *
 * There is no such thing as an EOF return.  If the end of the file has been
 * reached, the routine has a choice of ERREXIT() or inserting fake data into
 * the buffer.  In most cases, generating a warning message and inserting a
 * fake EOI marker is the best course of action --- this will allow the
 * decompressor to output however much of the image is there.  However,
 * the resulting error message is misleading if the real problem is an empty
 * input file, so we handle that case specially.
 *
 * In applications that need to be able to suspend compression due to input
 * not being available yet, a FALSE return indicates that no more data can be
 * obtained right now, but more may be forthcoming later.  In this situation,
 * the decompressor will return to its caller (with an indication of the
 * number of scanlines it has read, if any).  The application should resume
 * decompression after it has loaded more data into the input buffer.  Note
 * that there are substantial restrictions on the use of suspension --- see
 * the documentation.
 *
 * When suspending, the decompressor will back up to a convenient restart point
 * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
 * indicate where the restart point will be if the current call returns FALSE.
 * Data beyond this point must be rescanned after resumption, so move it to
 * the front of the buffer rather than discarding it.
 */

boolean my_source_mgr::fill_input_buffer(j_decompress_ptr cinfo)
{
	size_t nbytes = JFREAD(infile, buffer, INPUT_BUF_SIZE);

	if (nbytes <= 0) 
	{
		if ( start_of_file )	/* Treat empty input file as fatal error */
			cinfo->ERREXIT(JERR_INPUT_EMPTY);
		cinfo->WARNMS(JWRN_JPEG_EOF);
		/* Insert a fake EOI marker */
    
		buffer[0] = (JOCTET) 0xFF;
		buffer[1] = (JOCTET) JPEG_EOI;
		nbytes = 2;
	}

	next_input_byte = buffer;
	bytes_in_buffer = nbytes;
	start_of_file   = FALSE;

	return TRUE;
}


/*
 * Skip data --- used to skip over a potentially large amount of
 * uninteresting data (such as an APPn marker).
 *
 * Writers of suspendable-input applications must note that skip_input_data
 * is not granted the right to give a suspension return.  If the skip extends
 * beyond the data currently in the buffer, the buffer can be marked empty so
 * that the next read will cause a fill_input_buffer call that can suspend.
 * Arranging for additional bytes to be discarded before reloading the input
 * buffer is the application writer's problem.
 */

void my_source_mgr::skip_input_data (j_decompress_ptr cinfo, long num_bytes)
{
	/* Just a dumb implementation for now.  Could use fseek() except
	* it doesn't work on pipes.  Not clear that being smart is worth
	* any trouble anyway --- large skips are infrequent.
	*/
	if (num_bytes > 0) 
	{
		while (num_bytes > (long) bytes_in_buffer) 
		{
			num_bytes -= (long) bytes_in_buffer;
			fill_input_buffer(cinfo);
			/* note we assume that fill_input_buffer will never return FALSE,
			* so suspension need not be handled.
			*/
		}
		next_input_byte += (size_t) num_bytes;
		bytes_in_buffer -= (size_t) num_bytes;
	}
}


/*
 * An additional method that can be provided by data source modules is the
 * resync_to_restart method for error recovery in the presence of RST markers.
 * For the moment, this source module just uses the default resync method
 * provided by the JPEG library.  That method assumes that no backtracking
 * is possible.
 */


/*
 * Terminate source --- called by jpeg_finish_decompress
 * after all data has been read.  Often a no-op.
 *
 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
 * application must deal with any cleanup that should happen even
 * for error exit.
 */

void my_source_mgr::term_source (j_decompress_ptr cinfo)
{
	if (cinfo->src)
	{		
		delete (my_source_mgr *) cinfo->src;
		cinfo->src = NULL;
	}
}


/*
 * Prepare for input from a stdio stream.
 * The caller must have already opened the stream, and is responsible
 * for closing it after finishing decompression.
 */

GLOBAL(void) jpeg_stdio_src (j_decompress_ptr cinfo, FILE * infile)
{
	my_source_mgr * src;

	/* The source object and input buffer are made permanent so that a series
	* of JPEG images can be read from the same file by calling jpeg_stdio_src
	* only before the first one.  (If we discarded the buffer at the end of
	* one image, we'd likely lose the start of the next one.)
	* This makes it unsafe to use this manager and a different source
	* manager serially with the same JPEG object.  Caveat programmer.
	*/
	if (cinfo->src == NULL) // first time for this JPEG object? 
		cinfo->src = new my_source_mgr;

	src = (my_source_mgr *) cinfo->src;

	src->Reset(infile);
}


void jpeg_source_mgr::init_source(j_decompress_ptr cinfo)
{
	next_input_byte = NULL;
	bytes_in_buffer = 0;
}

boolean  jpeg_source_mgr::fill_input_buffer(j_decompress_ptr cinfo)
{
	return FALSE;
}

void jpeg_source_mgr::skip_input_data(j_decompress_ptr cinfo, long num_bytes)
{
	next_input_byte += num_bytes;
	bytes_in_buffer -= num_bytes;
}

void jpeg_source_mgr::term_source(j_decompress_ptr cinfo)
{
}


////////////////////////////////////
//   READ FROM A CONST BUFFER     //
////////////////////////////////////

class const_source_mgr : public jpeg_source_mgr
{

public :

	void Reset(const unsigned char * buffer, int len )
	{
		bytes_in_buffer = len; 
		next_input_byte = buffer;
	}
	
	void init_source(j_decompress_ptr cinfo)
	{
	}

	virtual void term_source(j_decompress_ptr cinfo)
	{
		if (cinfo->src)
		{		
			delete (const_source_mgr *) cinfo->src;
			cinfo->src = NULL;
		}
	}
};


/*
 * Prepare for input from a stdio stream.
 * The caller must have already opened the stream, and is responsible
 * for closing it after finishing decompression.
 */

GLOBAL(void) jpeg_const_src (j_decompress_ptr cinfo, const unsigned char * buffer, int len)
{
	const_source_mgr * src;

	if (cinfo->src == NULL) // first time for this JPEG object? 
		cinfo->src = new const_source_mgr;

	src = (const_source_mgr *) cinfo->src;

	src->Reset(buffer, len);
}