ref: bf5dc91f8d7bc2035effd18290c523050fa1b2cd
dir: /code/jpeg-6/jdtrans.c/
/*
* jdtrans.c
*
* Copyright (C) 1995, 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 library routines for transcoding decompression,
* that is, reading raw DCT coefficient arrays from an input JPEG file.
* The routines in jdapimin.c will also be needed by a transcoder.
*/
#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
/* Forward declarations */
LOCAL void transdecode_master_selection JPP((j_decompress_ptr cinfo));
/*
* Read the coefficient arrays from a JPEG file.
* jpeg_read_header must be completed before calling this.
*
* The entire image is read into a set of virtual coefficient-block arrays,
* one per component. The return value is a pointer to the array of
* virtual-array descriptors. These can be manipulated directly via the
* JPEG memory manager, or handed off to jpeg_write_coefficients().
* To release the memory occupied by the virtual arrays, call
* jpeg_finish_decompress() when done with the data.
*
* Returns NULL if suspended. This case need be checked only if
* a suspending data source is used.
*/
GLOBAL jvirt_barray_ptr *
jpeg_read_coefficients (j_decompress_ptr cinfo)
{
if (cinfo->global_state == DSTATE_READY) {
/* First call: initialize active modules */
transdecode_master_selection(cinfo);
cinfo->global_state = DSTATE_RDCOEFS;
} else if (cinfo->global_state != DSTATE_RDCOEFS)
ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
/* Absorb whole file into the coef buffer */
for (;;) {
int retcode;
/* Call progress monitor hook if present */
if (cinfo->progress != NULL)
(*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo);
/* Absorb some more input */
retcode = (*cinfo->inputctl->consume_input) (cinfo);
if (retcode == JPEG_SUSPENDED)
return NULL;
if (retcode == JPEG_REACHED_EOI)
break;
/* Advance progress counter if appropriate */
if (cinfo->progress != NULL &&
(retcode == JPEG_ROW_COMPLETED || retcode == JPEG_REACHED_SOS)) {
if (++cinfo->progress->pass_counter >= cinfo->progress->pass_limit) {
/* startup underestimated number of scans; ratchet up one scan */
cinfo->progress->pass_limit += (long) cinfo->total_iMCU_rows;
}
}
}
/* Set state so that jpeg_finish_decompress does the right thing */
cinfo->global_state = DSTATE_STOPPING;
return cinfo->coef->coef_arrays;
}
/*
* Master selection of decompression modules for transcoding.
* This substitutes for jdmaster.c's initialization of the full decompressor.
*/
LOCAL void
transdecode_master_selection (j_decompress_ptr cinfo)
{
/* Entropy decoding: either Huffman or arithmetic coding. */
if (cinfo->arith_code) {
ERREXIT(cinfo, JERR_ARITH_NOTIMPL);
} else {
if (cinfo->progressive_mode) {
#ifdef D_PROGRESSIVE_SUPPORTED
jinit_phuff_decoder(cinfo);
#else
ERREXIT(cinfo, JERR_NOT_COMPILED);
#endif
} else
jinit_huff_decoder(cinfo);
}
/* Always get a full-image coefficient buffer. */
jinit_d_coef_controller(cinfo, TRUE);
/* We can now tell the memory manager to allocate virtual arrays. */
(*cinfo->mem->realize_virt_arrays) ((j_common_ptr) cinfo);
/* Initialize input side of decompressor to consume first scan. */
(*cinfo->inputctl->start_input_pass) (cinfo);
/* Initialize progress monitoring. */
if (cinfo->progress != NULL) {
int nscans;
/* Estimate number of scans to set pass_limit. */
if (cinfo->progressive_mode) {
/* Arbitrarily estimate 2 interleaved DC scans + 3 AC scans/component. */
nscans = 2 + 3 * cinfo->num_components;
} else if (cinfo->inputctl->has_multiple_scans) {
/* For a nonprogressive multiscan file, estimate 1 scan per component. */
nscans = cinfo->num_components;
} else {
nscans = 1;
}
cinfo->progress->pass_counter = 0L;
cinfo->progress->pass_limit = (long) cinfo->total_iMCU_rows * nscans;
cinfo->progress->completed_passes = 0;
cinfo->progress->total_passes = 1;
}
}