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