chromium/third_party/libjpeg_turbo/jcprepct.c

/*
 * jcprepct.c
 *
 * This file is part of the Independent JPEG Group's software:
 * Copyright (C) 1994-1996, Thomas G. Lane.
 * libjpeg-turbo Modifications:
 * Copyright (C) 2022, D. R. Commander.
 * For conditions of distribution and use, see the accompanying README.ijg
 * file.
 *
 * This file contains the compression preprocessing controller.
 * This controller manages the color conversion, downsampling,
 * and edge expansion steps.
 *
 * Most of the complexity here is associated with buffering input rows
 * as required by the downsampler.  See the comments at the head of
 * jcsample.c for the downsampler's needs.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"


/* At present, jcsample.c can request context rows only for smoothing.
 * In the future, we might also need context rows for CCIR601 sampling
 * or other more-complex downsampling procedures.  The code to support
 * context rows should be compiled only if needed.
 */
#ifdef INPUT_SMOOTHING_SUPPORTED
#define CONTEXT_ROWS_SUPPORTED
#endif


/*
 * For the simple (no-context-row) case, we just need to buffer one
 * row group's worth of pixels for the downsampling step.  At the bottom of
 * the image, we pad to a full row group by replicating the last pixel row.
 * The downsampler's last output row is then replicated if needed to pad
 * out to a full iMCU row.
 *
 * When providing context rows, we must buffer three row groups' worth of
 * pixels.  Three row groups are physically allocated, but the row pointer
 * arrays are made five row groups high, with the extra pointers above and
 * below "wrapping around" to point to the last and first real row groups.
 * This allows the downsampler to access the proper context rows.
 * At the top and bottom of the image, we create dummy context rows by
 * copying the first or last real pixel row.  This copying could be avoided
 * by pointer hacking as is done in jdmainct.c, but it doesn't seem worth the
 * trouble on the compression side.
 */


/* Private buffer controller object */

my_prep_controller;

my_prep_ptr;


/*
 * Initialize for a processing pass.
 */

METHODDEF(void)
start_pass_prep(j_compress_ptr cinfo, J_BUF_MODE pass_mode)
{ … }


/*
 * Expand an image vertically from height input_rows to height output_rows,
 * by duplicating the bottom row.
 */

LOCAL(void)
expand_bottom_edge(JSAMPARRAY image_data, JDIMENSION num_cols, int input_rows,
                   int output_rows)
{ … }


/*
 * Process some data in the simple no-context case.
 *
 * Preprocessor output data is counted in "row groups".  A row group
 * is defined to be v_samp_factor sample rows of each component.
 * Downsampling will produce this much data from each max_v_samp_factor
 * input rows.
 */

METHODDEF(void)
pre_process_data(j_compress_ptr cinfo, JSAMPARRAY input_buf,
                 JDIMENSION *in_row_ctr, JDIMENSION in_rows_avail,
                 JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
                 JDIMENSION out_row_groups_avail)
{ … }


#ifdef CONTEXT_ROWS_SUPPORTED

/*
 * Process some data in the context case.
 */

METHODDEF(void)
pre_process_context(j_compress_ptr cinfo, JSAMPARRAY input_buf,
                    JDIMENSION *in_row_ctr, JDIMENSION in_rows_avail,
                    JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
                    JDIMENSION out_row_groups_avail)
{ … }


/*
 * Create the wrapped-around downsampling input buffer needed for context mode.
 */

LOCAL(void)
create_context_buffer(j_compress_ptr cinfo)
{ … }

#endif /* CONTEXT_ROWS_SUPPORTED */


/*
 * Initialize preprocessing controller.
 */

GLOBAL(void)
jinit_c_prep_controller(j_compress_ptr cinfo, boolean need_full_buffer)
{ … }