118 lines
4.1 KiB
C
118 lines
4.1 KiB
C
/*
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* jddeflts.c
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*
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* Copyright (C) 1991, 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 optional default-setting code for the JPEG decompressor.
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* User interfaces do not have to use this file, but those that don't use it
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* must know more about the innards of the JPEG code.
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*/
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#include "jinclude.h"
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/*
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* Reload the input buffer after it's been emptied, and return the next byte.
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* See the JGETC macro for calling conditions.
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*
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* This routine is used only if the system-dependent user interface passes
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* standard_buffering = TRUE to j_d_defaults. Otherwise, the UI must supply
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* a corresponding routine. Note that in any case, this routine is likely
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* to be used only for JFIF or similar serial-access JPEG file formats.
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* The input file control module for a random-access format such as TIFF/JPEG
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* would need to override the read_jpeg_data method with its own routine.
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*
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* This routine would need to be replaced if reading JPEG data from something
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* other than a stdio stream.
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*/
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METHODDEF int
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read_jpeg_data (decompress_info_ptr cinfo)
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{
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cinfo->next_input_byte = cinfo->input_buffer + MIN_UNGET;
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cinfo->bytes_in_buffer = (int) FREAD(cinfo->input_file,
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cinfo->next_input_byte,
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JPEG_BUF_SIZE);
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if (cinfo->bytes_in_buffer <= 0)
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ERREXIT(cinfo->emethods, "Unexpected EOF in JPEG file");
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return JGETC(cinfo);
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}
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/* Default parameter setup for decompression.
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*
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* User interfaces that don't choose to use this routine must do their
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* own setup of all these parameters. Alternately, you can call this
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* to establish defaults and then alter parameters selectively. This
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* is the recommended approach since, if we add any new parameters,
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* your code will still work (they'll be set to reasonable defaults).
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*
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* standard_buffering should be TRUE if the JPEG data is to come from
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* a stdio stream and the user interface isn't interested in changing
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* the normal input-buffering logic. If FALSE is passed, the user
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* interface must provide its own read_jpeg_data method and must
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* set up its own input buffer. (Alternately, you can pass TRUE to
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* let the buffer be allocated here, then override read_jpeg_data with
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* your own routine.)
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*/
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GLOBAL void
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j_d_defaults (decompress_info_ptr cinfo, boolean standard_buffering)
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/* NB: the external methods must already be set up. */
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{
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/* Default to RGB output */
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/* UI can override by changing out_color_space */
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cinfo->out_color_space = CS_RGB;
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cinfo->jpeg_color_space = CS_UNKNOWN;
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/* Setting any other value in jpeg_color_space overrides heuristics in */
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/* jrdjfif.c. That might be useful when reading non-JFIF JPEG files, */
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/* but ordinarily the UI shouldn't change it. */
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/* Default to no gamma correction of output */
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cinfo->output_gamma = 1.0;
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/* Default to no color quantization */
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cinfo->quantize_colors = FALSE;
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/* but set reasonable default parameters for quantization, */
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/* so that turning on quantize_colors is sufficient to do something useful */
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cinfo->two_pass_quantize = FALSE; /* may change to TRUE later */
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cinfo->use_dithering = TRUE;
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cinfo->desired_number_of_colors = 256;
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/* Default to no smoothing */
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cinfo->do_block_smoothing = FALSE;
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cinfo->do_pixel_smoothing = FALSE;
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if (standard_buffering) {
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/* Allocate memory for input buffer. */
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cinfo->input_buffer = (char *) (*cinfo->emethods->alloc_small)
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((size_t) (JPEG_BUF_SIZE + MIN_UNGET));
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cinfo->bytes_in_buffer = 0; /* initialize buffer to empty */
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/* Install standard buffer-reloading method. */
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cinfo->methods->read_jpeg_data = read_jpeg_data;
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}
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}
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/* This routine releases storage allocated by j_d_defaults.
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* Note that freeing the method pointer structs and the decompress_info_struct
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* itself are the responsibility of the user interface.
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*
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* standard_buffering must agree with what was passed to j_d_defaults.
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*/
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GLOBAL void
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j_d_free_defaults (decompress_info_ptr cinfo, boolean standard_buffering)
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{
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if (standard_buffering) {
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(*cinfo->emethods->free_small) ((void *) cinfo->input_buffer);
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}
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}
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