/* * Contains an input manager for a data stream for JPEG library * decompression. We don't want to use the jpeg_stdio_src() reader of * jpeglib because it takes a FILE* argument, which fails miserably * under certain circumstances when jpeglib is an MSWindows DLL. * * Based on example code found in the libjpeg archive, copyright * 1994-1996 by Thomas G. Lane. * * This file #include'd into simage_jpeg.c. * */ #include #include #define CHUNK_SIZE (64 * 1024) typedef struct { struct jpeg_source_mgr pub; FILE * infile; JOCTET * buffer; boolean start_of_file; } input_source_mgr; /* Called by jpeg_read_header(). */ static void init_source(j_decompress_ptr cinfo) { input_source_mgr * src = (input_source_mgr *)cinfo->src; src->start_of_file = TRUE; /* nothing else to do */ } /* * 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. */ static boolean fill_input_buffer(j_decompress_ptr cinfo) { input_source_mgr * src = (input_source_mgr *) cinfo->src; size_t nbytes = fread(src->buffer, 1, CHUNK_SIZE, src->infile); if (nbytes <= 0) { if (src->start_of_file) /* Treat empty input file as fatal error */ ERREXIT(cinfo, JERR_INPUT_EMPTY); WARNMS(cinfo, JWRN_JPEG_EOF); /* Insert a fake EOI marker */ src->buffer[0] = (JOCTET) 0xFF; src->buffer[1] = (JOCTET) JPEG_EOI; nbytes = 2; } src->pub.next_input_byte = src->buffer; src->pub.bytes_in_buffer = nbytes; src->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. */ static void skip_input_data(j_decompress_ptr cinfo, long num_bytes) { input_source_mgr * src = (input_source_mgr *) cinfo->src; /* 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) src->pub.bytes_in_buffer) { num_bytes -= (long) src->pub.bytes_in_buffer; (void) fill_input_buffer(cinfo); /* note we assume that fill_input_buffer will never return FALSE, * so suspension need not be handled. */ } src->pub.next_input_byte += (size_t) num_bytes; src->pub.bytes_in_buffer -= (size_t) num_bytes; } } /* * 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. */ static void term_source(j_decompress_ptr cinfo) { /* no work necessary here */ } static void simage_jpeg_src_init(j_decompress_ptr cinfo, FILE * infile) { input_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 = (struct jpeg_source_mgr *) (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT, sizeof(input_source_mgr)); src = (input_source_mgr *) cinfo->src; src->buffer = (JOCTET *) (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT, CHUNK_SIZE * sizeof(JOCTET)); } src = (input_source_mgr *) cinfo->src; src->pub.init_source = init_source; src->pub.fill_input_buffer = fill_input_buffer; src->pub.skip_input_data = skip_input_data; src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */ src->pub.term_source = term_source; src->infile = infile; src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */ src->pub.next_input_byte = NULL; /* until buffer loaded */ }