+++ /dev/null
-/*
- * 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 <stdio.h>
-
-/*
- * 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"
-
-/*
- * <setjmp.h> is used for the optional error recovery mechanism shown in
- * the second part of the example.
- */
-
-#include <setjmp.h>
-
-
-
-/******************** 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.
- */
projects / synfig.git / blobdiff