JPEGView/Independent JPEG Group/jcprepct.c

/*
 * jcprepct.c
 *
 * Copyright (C) 1994, 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 the compression preprocessing controller.
 * This controller manages the color conversion, downsampling,
 * and edge expansion steps.
 */

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


/* Private buffer controller object */

typedef struct {
  struct jpeg_c_prep_controller pub; /* public fields */

  /* Downsampling input buffer.  This buffer holds color-converted data
   * until we have enough to do a downsample step.
   */
  JSAMPARRAY color_buf[MAX_COMPONENTS];

  int rows_in_buf;		/* counts rows stored in color_buf */
  JDIMENSION rows_to_go;	/* counts rows remaining in source image */
} my_prep_controller;

typedef my_prep_controller * my_prep_ptr;


/*
 * Initialize for a processing pass.
 */

METHODDEF void
start_pass (j_compress_ptr cinfo, J_BUF_MODE pass_mode)
{
  my_prep_ptr prep = (my_prep_ptr) cinfo->prep;

  switch (pass_mode) {
  case JBUF_PASS_THRU:
    break;
  default:
    ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
    break;
  }

  /* Mark the conversion buffer empty */
  prep->rows_in_buf = 0;
  /* Initialize total-height counter for detecting bottom of image */
  prep->rows_to_go = cinfo->image_height;
}


/*
 * 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)
{
  register int row;

  for (row = input_rows; row < output_rows; row++) {
    jcopy_sample_rows(image_data, input_rows-1, image_data, row,
		      1, num_cols);
  }
}


/*
 * Process some data.
 *
 * 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)
{
  my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
  int numrows, ci;
  JDIMENSION inrows;
  jpeg_component_info * compptr;

  while (*in_row_ctr < in_rows_avail &&
	 *out_row_group_ctr < out_row_groups_avail) {
    /* Do color conversion to fill the conversion buffer. */
    inrows = in_rows_avail - *in_row_ctr;
    numrows = cinfo->max_v_samp_factor - prep->rows_in_buf;
    numrows = (int) MIN((JDIMENSION) numrows, inrows);
    (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
				       prep->color_buf,
				       (JDIMENSION) prep->rows_in_buf,
				       numrows);
    *in_row_ctr += numrows;
    prep->rows_in_buf += numrows;
    prep->rows_to_go -= numrows;
    /* If at bottom of image, pad to fill the conversion buffer. */
    if (prep->rows_to_go == 0 &&
	prep->rows_in_buf < cinfo->max_v_samp_factor) {
      for (ci = 0; ci < cinfo->num_components; ci++) {
	expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
			   prep->rows_in_buf, cinfo->max_v_samp_factor);
      }
      prep->rows_in_buf = cinfo->max_v_samp_factor;
    }
    /* If we've filled the conversion buffer, empty it. */
    if (prep->rows_in_buf == cinfo->max_v_samp_factor) {
      (*cinfo->downsample->downsample) (cinfo, prep->color_buf,
					output_buf, *out_row_group_ctr);
      prep->rows_in_buf = 0;
      (*out_row_group_ctr)++;
    }
    /* If at bottom of image, pad the output to a full MCU height.
     * Note we assume the caller is providing a one-MCU-height output buffer!
     */
    if (prep->rows_to_go == 0 &&
	*out_row_group_ctr < out_row_groups_avail) {
      for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
	   ci++, compptr++) {
	expand_bottom_edge(output_buf[ci],
			   compptr->width_in_blocks * DCTSIZE,
			   (int) (*out_row_group_ctr * compptr->v_samp_factor),