loadjpeg.c

DC的SEGA_GG模拟器源代码

#include <kos.h>
#include "jpeg/jpeg.h"
#include "jpeg-6b/jpeglib.h"

/* load n x n textures from jpegs */

int jjpeg_to_texture(char * filename, unsigned short *tex, int n, int scale)
{
    int i;
    unsigned short *ourbuffer;

    /* 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;
    
    struct jpeg_error_mgr jerr;
    
    /* More stuff */
    FILE * infile;                /* source file */
    JSAMPARRAY buffer;            /* Output row buffer */
    int row_stride;               /* physical row width in output buffer */
    
    ourbuffer = (unsigned short *)malloc(sizeof(unsigned short)*n);

    /* 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 */
    cinfo.err = jpeg_std_error(&jerr);
    
    /* 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 */
    
    cinfo.scale_denom = scale; /* must be 1, 2, 4, or 8 */

    /* 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);

	for(i=0; i<row_stride/3; i++)
	    ourbuffer[i] = ((buffer[0][i*3]>>3)<<11) + ((buffer[0][i*3+1]>>2)<<5) + (buffer[0][i*3+2]>>3);
	
	memcpy(tex + n*(cinfo.output_scanline-1), ourbuffer, 2*row_stride/3); 
    }
    
    /* 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).
     */

    free(ourbuffer);
    
    /* And we're done! */
    return 1;
}