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/* 
 * example.c 
 * 
 * This file illustrates how to use the IJG code as a subroutine library 
 * to read or write JPEG image files.  You should look at this code in 
 * conjunction with the documentation file libjpeg.doc. 
 * 
 * This code will not do anything useful as-is, but it may be helpful as a 
 * skeleton for constructing routines that call the JPEG library.   
 * 
 * We present these routines in the same coding style used in the JPEG code 
 * (ANSI function definitions, etc); but you are of course free to code your 
 * routines in a different style if you prefer. 
 */ 
 
#include  
 
/* 
 * Include file for users of JPEG library. 
 * You will need to have included system headers that define at least 
 * the typedefs FILE and size_t before you can include jpeglib.h. 
 * (stdio.h is sufficient on ANSI-conforming systems.) 
 * You may also wish to include "jerror.h". 
 */ 
 
#include "jpeglib.h" 
 
/* 
 *  is used for the optional error recovery mechanism shown in 
 * the second part of the example. 
 */ 
 
#include  
 
 
 
/******************** JPEG COMPRESSION SAMPLE INTERFACE *******************/ 
 
/* This half of the example shows how to feed data into the JPEG compressor. 
 * We present a minimal version that does not worry about refinements such 
 * as error recovery (the JPEG code will just exit() if it gets an error). 
 */ 
 
 
/* 
 * IMAGE DATA FORMATS: 
 * 
 * The standard input image format is a rectangular array of pixels, with 
 * each pixel having the same number of "component" values (color channels). 
 * Each pixel row is an array of JSAMPLEs (which typically are unsigned chars). 
 * If you are working with color data, then the color values for each pixel 
 * must be adjacent in the row; for example, R,G,B,R,G,B,R,G,B,... for 24-bit 
 * RGB color. 
 * 
 * For this example, we'll assume that this data structure matches the way 
 * our application has stored the image in memory, so we can just pass a 
 * pointer to our image buffer.  In particular, let's say that the image is 
 * RGB color and is described by: 
 */ 
 
extern JSAMPLE * image_buffer;	/* Points to large array of R,G,B-order data */ 
extern int image_height;	/* Number of rows in image */ 
extern int image_width;		/* Number of columns in image */ 
 
 
/* 
 * Sample routine for JPEG compression.  We assume that the target file name 
 * and a compression quality factor are passed in. 
 */ 
 
GLOBAL(void) 
write_JPEG_file (char * filename, int quality) 
{ 
  /* This struct contains the JPEG compression parameters and pointers to 
   * working space (which is allocated as needed by the JPEG library). 
   * It is possible to have several such structures, representing multiple 
   * compression/decompression processes, in existence at once.  We refer 
   * to any one struct (and its associated working data) as a "JPEG object". 
   */ 
  struct jpeg_compress_struct cinfo; 
  /* This struct represents a JPEG error handler.  It is declared separately 
   * because applications often want to supply a specialized error handler 
   * (see the second half of this file for an example).  But here we just 
   * take the easy way out and use the standard error handler, which will 
   * print a message on stderr and call exit() if compression fails. 
   * Note that this struct must live as long as the main JPEG parameter 
   * struct, to avoid dangling-pointer problems. 
   */ 
  struct jpeg_error_mgr jerr; 
  /* More stuff */ 
  FILE * outfile;		/* target file */ 
  JSAMPROW row_pointer[1];	/* pointer to JSAMPLE row[s] */ 
  int row_stride;		/* physical row width in image buffer */ 
 
  /* Step 1: allocate and initialize JPEG compression object */ 
 
  /* We have to set up the error handler first, in case the initialization 
   * step fails.  (Unlikely, but it could happen if you are out of memory.) 
   * This routine fills in the contents of struct jerr, and returns jerr's 
   * address which we place into the link field in cinfo. 
   */ 
  cinfo.err = jpeg_std_error(&jerr); 
  /* Now we can initialize the JPEG compression object. */ 
  jpeg_create_compress(&cinfo); 
 
  /* Step 2: specify data destination (eg, a file) */ 
  /* Note: steps 2 and 3 can be done in either order. */ 
 
  /* Here we use the library-supplied code to send compressed data to a 
   * stdio stream.  You can also write your own code to do something else. 
   * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that 
   * requires it in order to write binary files. 
   */ 
  if ((outfile = fopen(filename, "wb")) == NULL) { 
    fprintf(stderr, "can't open %s\n", filename); 
    exit(1); 
  } 
  jpeg_stdio_dest(&cinfo, outfile); 
 
  /* Step 3: set parameters for compression */ 
 
  /* First we supply a description of the input image. 
   * Four fields of the cinfo struct must be filled in: 
   */ 
  cinfo.image_width = image_width; 	/* image width and height, in pixels */ 
  cinfo.image_height = image_height; 
  cinfo.input_components = 3;		/* # of color components per pixel */ 
  cinfo.in_color_space = JCS_RGB; 	/* colorspace of input image */ 
  /* Now use the library's routine to set default compression parameters. 
   * (You must set at least cinfo.in_color_space before calling this, 
   * since the defaults depend on the source color space.) 
   */ 
  jpeg_set_defaults(&cinfo); 
  /* Now you can set any non-default parameters you wish to. 
   * Here we just illustrate the use of quality (quantization table) scaling: 
   */ 
  jpeg_set_quality(&cinfo, quality, TRUE /* limit to baseline-JPEG values */); 
 
  /* Step 4: Start compressor */ 
 
  /* TRUE ensures that we will write a complete interchange-JPEG file. 
   * Pass TRUE unless you are very sure of what you're doing. 
   */ 
  jpeg_start_compress(&cinfo, TRUE); 
 
  /* Step 5: while (scan lines remain to be written) */ 
  /*           jpeg_write_scanlines(...); */ 
 
  /* Here we use the library's state variable cinfo.next_scanline as the 
   * loop counter, so that we don't have to keep track ourselves. 
   * To keep things simple, we pass one scanline per call; you can pass 
   * more if you wish, though. 
   */ 
  row_stride = image_width * 3;	/* JSAMPLEs per row in image_buffer */ 
 
  while (cinfo.next_scanline < cinfo.image_height) { 
    /* jpeg_write_scanlines expects an array of pointers to scanlines. 
     * Here the array is only one element long, but you could pass 
     * more than one scanline at a time if that's more convenient. 
     */ 
    row_pointer[0] = & image_buffer[cinfo.next_scanline * row_stride]; 
    (void) jpeg_write_scanlines(&cinfo, row_pointer, 1); 
  } 
 
  /* Step 6: Finish compression */ 
 
  jpeg_finish_compress(&cinfo); 
  /* After finish_compress, we can close the output file. */ 
  fclose(outfile); 
 
  /* Step 7: release JPEG compression object */ 
 
  /* This is an important step since it will release a good deal of memory. */ 
  jpeg_destroy_compress(&cinfo); 
 
  /* And we're done! */ 
} 
 
 
/* 
 * SOME FINE POINTS: 
 * 
 * In the above loop, we ignored the return value of jpeg_write_scanlines, 
 * which is the number of scanlines actually written.  We could get away 
 * with this because we were only relying on the value of cinfo.next_scanline, 
 * which will be incremented correctly.  If you maintain additional loop 
 * variables then you should be careful to increment them properly. 
 * Actually, for output to a stdio stream you needn't worry, because 
 * then jpeg_write_scanlines will write all the lines passed (or else exit 
 * with a fatal error).  Partial writes can only occur if you use a data 
 * destination module that can demand suspension of the compressor. 
 * (If you don't know what that's for, you don't need it.) 
 * 
 * If the compressor requires full-image buffers (for entropy-coding 
 * optimization or a multi-scan JPEG file), it will create temporary 
 * files for anything that doesn't fit within the maximum-memory setting. 
 * (Note that temp files are NOT needed if you use the default parameters.) 
 * On some systems you may need to set up a signal handler to ensure that 
 * temporary files are deleted if the program is interrupted.  See libjpeg.doc. 
 * 
 * Scanlines MUST be supplied in top-to-bottom order if you want your JPEG 
 * files to be compatible with everyone else's.  If you cannot readily read 
 * your data in that order, you'll need an intermediate array to hold the 
 * image.  See rdtarga.c or rdbmp.c for examples of handling bottom-to-top 
 * source data using the JPEG code's internal virtual-array mechanisms. 
 */ 
 
 
 
/******************** JPEG DECOMPRESSION SAMPLE INTERFACE *******************/ 
 
/* This half of the example shows how to read data from the JPEG decompressor. 
 * It's a bit more refined than the above, in that we show: 
 *   (a) how to modify the JPEG library's standard error-reporting behavior; 
 *   (b) how to allocate workspace using the library's memory manager. 
 * 
 * Just to make this example a little different from the first one, we'll 
 * assume that we do not intend to put the whole image into an in-memory 
 * buffer, but to send it line-by-line someplace else.  We need a one- 
 * scanline-high JSAMPLE array as a work buffer, and we will let the JPEG 
 * memory manager allocate it for us.  This approach is actually quite useful 
 * because we don't need to remember to deallocate the buffer separately: it 
 * will go away automatically when the JPEG object is cleaned up. 
 */ 
 
 
/* 
 * ERROR HANDLING: 
 * 
 * The JPEG library's standard error handler (jerror.c) is divided into 
 * several "methods" which you can override individually.  This lets you 
 * adjust the behavior without duplicating a lot of code, which you might 
 * have to update with each future release. 
 * 
 * Our example here shows how to override the "error_exit" method so that 
 * control is returned to the library's caller when a fatal error occurs, 
 * rather than calling exit() as the standard error_exit method does. 
 * 
 * We use C's setjmp/longjmp facility to return control.  This means that the 
 * routine which calls the JPEG library must first execute a setjmp() call to 
 * establish the return point.  We want the replacement error_exit to do a 
 * longjmp().  But we need to make the setjmp buffer accessible to the 
 * error_exit routine.  To do this, we make a private extension of the 
 * standard JPEG error handler object.  (If we were using C++, we'd say we 
 * were making a subclass of the regular error handler.) 
 * 
 * Here's the extended error handler struct: 
 */ 
 
struct my_error_mgr { 
  struct jpeg_error_mgr pub;	/* "public" fields */ 
 
  jmp_buf setjmp_buffer;	/* for return to caller */ 
}; 
 
typedef struct my_error_mgr * my_error_ptr; 
 
/* 
 * Here's the routine that will replace the standard error_exit method: 
 */ 
 
METHODDEF(void) 
my_error_exit (j_common_ptr cinfo) 
{ 
  /* cinfo->err really points to a my_error_mgr struct, so coerce pointer */ 
  my_error_ptr myerr = (my_error_ptr) cinfo->err; 
 
  /* Always display the message. */ 
  /* We could postpone this until after returning, if we chose. */ 
  (*cinfo->err->output_message) (cinfo); 
 
  /* Return control to the setjmp point */ 
  longjmp(myerr->setjmp_buffer, 1); 
} 
 
 
/* 
 * Sample routine for JPEG decompression.  We assume that the source file name 
 * is passed in.  We want to return 1 on success, 0 on error. 
 */ 
 
 
GLOBAL(int) 
read_JPEG_file (char * filename) 
{ 
  /* This struct contains the JPEG decompression parameters and pointers to 
   * working space (which is allocated as needed by the JPEG library). 
   */ 
  struct jpeg_decompress_struct cinfo; 
  /* We use our private extension JPEG error handler. 
   * Note that this struct must live as long as the main JPEG parameter 
   * struct, to avoid dangling-pointer problems. 
   */ 
  struct my_error_mgr jerr; 
  /* More stuff */ 
  FILE * infile;		/* source file */ 
  JSAMPARRAY buffer;		/* Output row buffer */ 
  int row_stride;		/* physical row width in output buffer */ 
 
  /* In this example we want to open the input file before doing anything else, 
   * so that the setjmp() error recovery below can assume the file is open. 
   * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that 
   * requires it in order to read binary files. 
   */ 
 
  if ((infile = fopen(filename, "rb")) == NULL) { 
    fprintf(stderr, "can't open %s\n", filename); 
    return 0; 
  } 
 
  /* Step 1: allocate and initialize JPEG decompression object */ 
 
  /* We set up the normal JPEG error routines, then override error_exit. */ 
  cinfo.err = jpeg_std_error(&jerr.pub); 
  jerr.pub.error_exit = my_error_exit; 
  /* Establish the setjmp return context for my_error_exit to use. */ 
  if (setjmp(jerr.setjmp_buffer)) { 
    /* If we get here, the JPEG code has signaled an error. 
     * We need to clean up the JPEG object, close the input file, and return. 
     */ 
    jpeg_destroy_decompress(&cinfo); 
    fclose(infile); 
    return 0; 
  } 
  /* Now we can initialize the JPEG decompression object. */ 
  jpeg_create_decompress(&cinfo); 
 
  /* Step 2: specify data source (eg, a file) */ 
 
  jpeg_stdio_src(&cinfo, infile); 
 
  /* Step 3: read file parameters with jpeg_read_header() */ 
 
  (void) jpeg_read_header(&cinfo, TRUE); 
  /* We can ignore the return value from jpeg_read_header since 
   *   (a) suspension is not possible with the stdio data source, and 
   *   (b) we passed TRUE to reject a tables-only JPEG file as an error. 
   * See libjpeg.doc for more info. 
   */ 
 
  /* Step 4: set parameters for decompression */ 
 
  /* In this example, we don't need to change any of the defaults set by 
   * jpeg_read_header(), so we do nothing here. 
   */ 
 
  /* Step 5: Start decompressor */ 
 
  (void) jpeg_start_decompress(&cinfo); 
  /* We can ignore the return value since suspension is not possible 
   * with the stdio data source. 
   */ 
 
  /* We may need to do some setup of our own at this point before reading 
   * the data.  After jpeg_start_decompress() we have the correct scaled 
   * output image dimensions available, as well as the output colormap 
   * if we asked for color quantization. 
   * In this example, we need to make an output work buffer of the right size. 
   */  
  /* JSAMPLEs per row in output buffer */ 
  row_stride = cinfo.output_width * cinfo.output_components; 
  /* Make a one-row-high sample array that will go away when done with image */ 
  buffer = (*cinfo.mem->alloc_sarray) 
		((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1); 
 
  /* Step 6: while (scan lines remain to be read) */ 
  /*           jpeg_read_scanlines(...); */ 
 
  /* Here we use the library's state variable cinfo.output_scanline as the 
   * loop counter, so that we don't have to keep track ourselves. 
   */ 
  while (cinfo.output_scanline < cinfo.output_height) { 
    /* jpeg_read_scanlines expects an array of pointers to scanlines. 
     * Here the array is only one element long, but you could ask for 
     * more than one scanline at a time if that's more convenient. 
     */ 
    (void) jpeg_read_scanlines(&cinfo, buffer, 1); 
    /* Assume put_scanline_someplace wants a pointer and sample count. */ 
    put_scanline_someplace(buffer[0], row_stride); 
  } 
 
  /* Step 7: Finish decompression */ 
 
  (void) jpeg_finish_decompress(&cinfo); 
  /* We can ignore the return value since suspension is not possible 
   * with the stdio data source. 
   */ 
 
  /* Step 8: Release JPEG decompression object */ 
 
  /* This is an important step since it will release a good deal of memory. */ 
  jpeg_destroy_decompress(&cinfo); 
 
  /* After finish_decompress, we can close the input file. 
   * Here we postpone it until after no more JPEG errors are possible, 
   * so as to simplify the setjmp error logic above.  (Actually, I don't 
   * think that jpeg_destroy can do an error exit, but why assume anything...) 
   */ 
  fclose(infile); 
 
  /* At this point you may want to check to see whether any corrupt-data 
   * warnings occurred (test whether jerr.pub.num_warnings is nonzero). 
   */ 
 
  /* And we're done! */ 
  return 1; 
} 
 
 
/* 
 * SOME FINE POINTS: 
 * 
 * In the above code, we ignored the return value of jpeg_read_scanlines, 
 * which is the number of scanlines actually read.  We could get away with 
 * this because we asked for only one line at a time and we weren't using 
 * a suspending data source.  See libjpeg.doc for more info. 
 * 
 * We cheated a bit by calling alloc_sarray() after jpeg_start_decompress(); 
 * we should have done it beforehand to ensure that the space would be 
 * counted against the JPEG max_memory setting.  In some systems the above 
 * code would risk an out-of-memory error.  However, in general we don't 
 * know the output image dimensions before jpeg_start_decompress(), unless we 
 * call jpeg_calc_output_dimensions().  See libjpeg.doc for more about this. 
 * 
 * Scanlines are returned in the same order as they appear in the JPEG file, 
 * which is standardly top-to-bottom.  If you must emit data bottom-to-top, 
 * you can use one of the virtual arrays provided by the JPEG memory manager 
 * to invert the data.  See wrbmp.c for an example. 
 * 
 * As with compression, some operating modes may require temporary files. 
 * On some systems you may need to set up a signal handler to ensure that 
 * temporary files are deleted if the program is interrupted.  See libjpeg.doc. 
 */