src/jpeg/jcprepct.c

/*
 * jcprepct.c
 *
 * Copyright (C) 1994-1996, 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.
 *
 * 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 */

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];

  JDIMENSION rows_to_go;	/* counts rows remaining in source image */
  int next_buf_row;		/* index of next row to store in color_buf */

#ifdef CONTEXT_ROWS_SUPPORTED	/* only needed for context case */
  int this_row_group;		/* starting row index of group to process */
  int next_buf_stop;		/* downsample when we reach this index */
#endif
} my_prep_controller;

typedef 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)
{
  my_prep_ptr prep = (my_prep_ptr) cinfo->prep;

  if (pass_mode != JBUF_PASS_THRU)
    ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);

  /* Initialize total-height counter for detecting bottom of image */
  prep->rows_to_go = cinfo->image_height;
  /* Mark the conversion buffer empty */
  prep->next_buf_row = 0;
#ifdef CONTEXT_ROWS_SUPPORTED
  /* Preset additional state variables for context mode.
   * These aren't used in non-context mode, so we needn't test which mode.
   */
  prep->this_row_group = 0;
  /* Set next_buf_stop to stop after two row groups have been read in. */
  prep->next_buf_stop = 2 * cinfo->max_v_samp_factor;
#endif
}


/*
 * 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 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)
{
  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->next_buf_row;
    numrows = (int) MIN((JDIMENSION) numrows, inrows);
    (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
				       prep->color_buf,
				       (JDIMENSION) prep->next_buf_row,
				       numrows);
    *in_row_ctr += numrows;
    prep->next_buf_row += numrows;
    prep->rows_to_go -= numrows;
    /* If at bottom of image, pad to fill the conversion buffer. */
    if (prep->rows_to_go == 0 &&
	prep->next_buf_row < cinfo->max_v_samp_factor) {
      for (ci = 0; ci < cinfo->num_components; ci++) {
	expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
			   prep->next_buf_row, cinfo->max_v_samp_factor);
      }
      prep->next_buf_row = cinfo->max_v_samp_factor;
    }
    /* If we've filled the conversion buffer, empty it. */
    if (prep->next_buf_row == cinfo->max_v_samp_factor) {
      (*cinfo->downsample->downsample) (cinfo,
					prep->color_buf, (JDIMENSION) 0,
					output_buf, *out_row_group_ctr);
      prep->next_buf_row = 0;
      (*out_row_group_ctr)++;
    }
    /* If at bottom of image, pad the output to a full iMCU height.
     * Note we assume the caller is providing a one-iMCU-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),
			   (int) (out_row_groups_avail * compptr->v_samp_factor));
      }
      *out_row_group_ctr = out_row_groups_avail;
      break;			/* can exit outer loop without test */
    }
  }
}


#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)
{
  my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
  int numrows, ci;
  int buf_height = cinfo->max_v_samp_factor * 3;
  JDIMENSION inrows;

  while (*out_row_group_ctr < out_row_groups_avail) {
    if (*in_row_ctr < in_rows_avail) {
      /* Do color conversion to fill the conversion buffer. */
      inrows = in_rows_avail - *in_row_ctr;
      numrows = prep->next_buf_stop - prep->next_buf_row;
      numrows = (int) MIN((JDIMENSION) numrows, inrows);
      (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
					 prep->color_buf,
					 (JDIMENSION) prep->next_buf_row,
					 numrows);
      /* Pad at top of image, if first time through */
      if (prep->rows_to_go == cinfo->image_height) {
	for (ci = 0; ci < cinfo->num_components; ci++) {
	  int row;
	  for (row = 1; row <= cinfo->max_v_samp_factor; row++) {
	    jcopy_sample_rows(prep->color_buf[ci], 0,
			      prep->color_buf[ci], -row,
			      1, cinfo->image_width);
	  }
	}
      }
      *in_row_ctr += numrows;
      prep->next_buf_row += numrows;
      prep->rows_to_go -= numrows;
    } else {
      /* Return for more data, unless we are at the bottom of the image. */
      if (prep->rows_to_go != 0)
	break;
      /* When at bottom of image, pad to fill the conversion buffer. */
      if (prep->next_buf_row < prep->next_buf_stop) {
	for (ci = 0; ci < cinfo->num_components; ci++) {
	  expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
			     prep->next_buf_row, prep->next_buf_stop);
	}
	prep->next_buf_row = prep->next_buf_stop;
      }
    }
    /* If we've gotten enough data, downsample a row group. */
    if (prep->next_buf_row == prep->next_buf_stop) {
      (*cinfo->downsample->downsample) (cinfo,
					prep->color_buf,
					(JDIMENSION) prep->this_row_group,
					output_buf, *out_row_group_ctr);
      (*out_row_group_ctr)++;
      /* Advance pointers with wraparound as necessary. */
      prep->this_row_group += cinfo->max_v_samp_factor;
      if (prep->this_row_group >= buf_height)
	prep->this_row_group = 0;
      if (prep->next_buf_row >= buf_height)
	prep->next_buf_row = 0;
      prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor;
    }
  }
}


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

LOCAL(void)
create_context_buffer (j_compress_ptr cinfo)
{
  my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
  int rgroup_height = cinfo->max_v_samp_factor;
  int ci, i;
  jpeg_component_info * compptr;
  JSAMPARRAY true_buffer, fake_buffer;

  /* Grab enough space for fake row pointers for all the components;
   * we need five row groups' worth of pointers for each component.
   */
  fake_buffer = (JSAMPARRAY)
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
				(cinfo->num_components * 5 * rgroup_height) *
				SIZEOF(JSAMPROW));

  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
       ci++, compptr++) {
    /* Allocate the actual buffer space (3 row groups) for this component.
     * We make the buffer wide enough to allow the downsampler to edge-expand
     * horizontally within the buffer, if it so chooses.
     */
    true_buffer = (*cinfo->mem->alloc_sarray)
      ((j_common_ptr) cinfo, JPOOL_IMAGE,
       (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
		      cinfo->max_h_samp_factor) / compptr->h_samp_factor),
       (JDIMENSION) (3 * rgroup_height));
    /* Copy true buffer row pointers into the middle of the fake row array */
    MEMCOPY(fake_buffer + rgroup_height, true_buffer,
	    3 * rgroup_height * SIZEOF(JSAMPROW));
    /* Fill in the above and below wraparound pointers */
    for (i = 0; i < rgroup_height; i++) {
      fake_buffer[i] = true_buffer[2 * rgroup_height + i];
      fake_buffer[4 * rgroup_height + i] = true_buffer[i];
    }
    prep->color_buf[ci] = fake_buffer + rgroup_height;
    fake_buffer += 5 * rgroup_height; /* point to space for next component */
  }
}

#endif /* CONTEXT_ROWS_SUPPORTED */


/*
 * Initialize preprocessing controller.
 */

GLOBAL(void)
jinit_c_prep_controller (j_compress_ptr cinfo, boolean need_full_buffer)
{
  my_prep_ptr prep;
  int ci;
  jpeg_component_info * compptr;

  if (need_full_buffer)		/* safety check */
    ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);

  prep = (my_prep_ptr)
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
				SIZEOF(my_prep_controller));
  cinfo->prep = (struct jpeg_c_prep_controller *) prep;
  prep->pub.start_pass = start_pass_prep;

  /* Allocate the color conversion buffer.
   * We make the buffer wide enough to allow the downsampler to edge-expand
   * horizontally within the buffer, if it so chooses.
   */
  if (cinfo->downsample->need_context_rows) {
    /* Set up to provide context rows */
#ifdef CONTEXT_ROWS_SUPPORTED
    prep->pub.pre_process_data = pre_process_context;
    create_context_buffer(cinfo);
#else
    ERREXIT(cinfo, JERR_NOT_COMPILED);
#endif
  } else {
    /* No context, just make it tall enough for one row group */
    prep->pub.pre_process_data = pre_process_data;
    for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
	 ci++, compptr++) {
      prep->color_buf[ci] = (*cinfo->mem->alloc_sarray)
	((j_common_ptr) cinfo, JPOOL_IMAGE,
	 (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
			cinfo->max_h_samp_factor) / compptr->h_samp_factor),
	 (JDIMENSION) cinfo->max_v_samp_factor);
    }
  }
}
Commit	Line	Data
	1	/*
	2	* jcprepct.c
	3	*
	4	* Copyright (C) 1994-1996, Thomas G. Lane.
	5	* This file is part of the Independent JPEG Group's software.
	6	* For conditions of distribution and use, see the accompanying README file.
	7	*
	8	* This file contains the compression preprocessing controller.
	9	* This controller manages the color conversion, downsampling,
	10	* and edge expansion steps.
	11	*
	12	* Most of the complexity here is associated with buffering input rows
	13	* as required by the downsampler. See the comments at the head of
	14	* jcsample.c for the downsampler's needs.
	15	*/
	16
	17	#define JPEG_INTERNALS
	18	#include "jinclude.h"
	19	#include "jpeglib.h"
	20
	21
	22	/* At present, jcsample.c can request context rows only for smoothing.
	23	* In the future, we might also need context rows for CCIR601 sampling
	24	* or other more-complex downsampling procedures. The code to support
	25	* context rows should be compiled only if needed.
	26	*/
	27	#ifdef INPUT_SMOOTHING_SUPPORTED
	28	#define CONTEXT_ROWS_SUPPORTED
	29	#endif
	30
	31
	32	/*
	33	* For the simple (no-context-row) case, we just need to buffer one
	34	* row group's worth of pixels for the downsampling step. At the bottom of
	35	* the image, we pad to a full row group by replicating the last pixel row.
	36	* The downsampler's last output row is then replicated if needed to pad
	37	* out to a full iMCU row.
	38	*
	39	* When providing context rows, we must buffer three row groups' worth of
	40	* pixels. Three row groups are physically allocated, but the row pointer
	41	* arrays are made five row groups high, with the extra pointers above and
	42	* below "wrapping around" to point to the last and first real row groups.
	43	* This allows the downsampler to access the proper context rows.
	44	* At the top and bottom of the image, we create dummy context rows by
	45	* copying the first or last real pixel row. This copying could be avoided
	46	* by pointer hacking as is done in jdmainct.c, but it doesn't seem worth the
	47	* trouble on the compression side.
	48	*/
	49
	50
	51	/* Private buffer controller object */
	52
	53	typedef struct {
	54	struct jpeg_c_prep_controller pub; /* public fields */
	55
	56	/* Downsampling input buffer. This buffer holds color-converted data
	57	* until we have enough to do a downsample step.
	58	*/
	59	JSAMPARRAY color_buf[MAX_COMPONENTS];
	60
	61	JDIMENSION rows_to_go; /* counts rows remaining in source image */
	62	int next_buf_row; /* index of next row to store in color_buf */
	63
	64	#ifdef CONTEXT_ROWS_SUPPORTED /* only needed for context case */
	65	int this_row_group; /* starting row index of group to process */
	66	int next_buf_stop; /* downsample when we reach this index */
	67	#endif
	68	} my_prep_controller;
	69
	70	typedef my_prep_controller * my_prep_ptr;
	71
	72
	73	/*
	74	* Initialize for a processing pass.
	75	*/
	76
	77	METHODDEF(void)
	78	start_pass_prep (j_compress_ptr cinfo, J_BUF_MODE pass_mode)
	79	{
	80	my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
	81
	82	if (pass_mode != JBUF_PASS_THRU)
	83	ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
	84
	85	/* Initialize total-height counter for detecting bottom of image */
	86	prep->rows_to_go = cinfo->image_height;
	87	/* Mark the conversion buffer empty */
	88	prep->next_buf_row = 0;
	89	#ifdef CONTEXT_ROWS_SUPPORTED
	90	/* Preset additional state variables for context mode.
	91	* These aren't used in non-context mode, so we needn't test which mode.
	92	*/
	93	prep->this_row_group = 0;
	94	/* Set next_buf_stop to stop after two row groups have been read in. */
	95	prep->next_buf_stop = 2 * cinfo->max_v_samp_factor;
	96	#endif
	97	}
	98
	99
	100	/*
	101	* Expand an image vertically from height input_rows to height output_rows,
	102	* by duplicating the bottom row.
	103	*/
	104
	105	LOCAL(void)
	106	expand_bottom_edge (JSAMPARRAY image_data, JDIMENSION num_cols,
	107	int input_rows, int output_rows)
	108	{
	109	register int row;
	110
	111	for (row = input_rows; row < output_rows; row++) {
	112	jcopy_sample_rows(image_data, input_rows-1, image_data, row,
	113	1, num_cols);
	114	}
	115	}
	116
	117
	118	/*
	119	* Process some data in the simple no-context case.
	120	*
	121	* Preprocessor output data is counted in "row groups". A row group
	122	* is defined to be v_samp_factor sample rows of each component.
	123	* Downsampling will produce this much data from each max_v_samp_factor
	124	* input rows.
	125	*/
	126
	127	METHODDEF(void)
	128	pre_process_data (j_compress_ptr cinfo,
	129	JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
	130	JDIMENSION in_rows_avail,
	131	JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
	132	JDIMENSION out_row_groups_avail)
	133	{
	134	my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
	135	int numrows, ci;
	136	JDIMENSION inrows;
	137	jpeg_component_info * compptr;
	138
	139	while (*in_row_ctr < in_rows_avail &&
	140	*out_row_group_ctr < out_row_groups_avail) {
	141	/* Do color conversion to fill the conversion buffer. */
	142	inrows = in_rows_avail - *in_row_ctr;
	143	numrows = cinfo->max_v_samp_factor - prep->next_buf_row;
	144	numrows = (int) MIN((JDIMENSION) numrows, inrows);
	145	(cinfo->cconvert->color_convert) (cinfo, input_buf + in_row_ctr,
	146	prep->color_buf,
	147	(JDIMENSION) prep->next_buf_row,
	148	numrows);
	149	*in_row_ctr += numrows;
	150	prep->next_buf_row += numrows;
	151	prep->rows_to_go -= numrows;
	152	/* If at bottom of image, pad to fill the conversion buffer. */
	153	if (prep->rows_to_go == 0 &&
	154	prep->next_buf_row < cinfo->max_v_samp_factor) {
	155	for (ci = 0; ci < cinfo->num_components; ci++) {
	156	expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
	157	prep->next_buf_row, cinfo->max_v_samp_factor);
	158	}
	159	prep->next_buf_row = cinfo->max_v_samp_factor;
	160	}
	161	/* If we've filled the conversion buffer, empty it. */
	162	if (prep->next_buf_row == cinfo->max_v_samp_factor) {
	163	(*cinfo->downsample->downsample) (cinfo,
	164	prep->color_buf, (JDIMENSION) 0,
	165	output_buf, *out_row_group_ctr);
	166	prep->next_buf_row = 0;
	167	(*out_row_group_ctr)++;
	168	}
	169	/* If at bottom of image, pad the output to a full iMCU height.
	170	* Note we assume the caller is providing a one-iMCU-height output buffer!
	171	*/
	172	if (prep->rows_to_go == 0 &&
	173	*out_row_group_ctr < out_row_groups_avail) {
	174	for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
	175	ci++, compptr++) {
	176	expand_bottom_edge(output_buf[ci],
	177	compptr->width_in_blocks * DCTSIZE,
	178	(int) (out_row_group_ctr compptr->v_samp_factor),
	179	(int) (out_row_groups_avail * compptr->v_samp_factor));
	180	}
	181	*out_row_group_ctr = out_row_groups_avail;
	182	break; /* can exit outer loop without test */
	183	}
	184	}
	185	}
	186
	187
	188	#ifdef CONTEXT_ROWS_SUPPORTED
	189
	190	/*
	191	* Process some data in the context case.
	192	*/
	193
	194	METHODDEF(void)
	195	pre_process_context (j_compress_ptr cinfo,
	196	JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
	197	JDIMENSION in_rows_avail,
	198	JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
	199	JDIMENSION out_row_groups_avail)
	200	{
	201	my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
	202	int numrows, ci;
	203	int buf_height = cinfo->max_v_samp_factor * 3;
	204	JDIMENSION inrows;
	205
	206	while (*out_row_group_ctr < out_row_groups_avail) {
	207	if (*in_row_ctr < in_rows_avail) {
	208	/* Do color conversion to fill the conversion buffer. */
	209	inrows = in_rows_avail - *in_row_ctr;
	210	numrows = prep->next_buf_stop - prep->next_buf_row;
	211	numrows = (int) MIN((JDIMENSION) numrows, inrows);
	212	(cinfo->cconvert->color_convert) (cinfo, input_buf + in_row_ctr,
	213	prep->color_buf,
	214	(JDIMENSION) prep->next_buf_row,
	215	numrows);
	216	/* Pad at top of image, if first time through */
	217	if (prep->rows_to_go == cinfo->image_height) {
	218	for (ci = 0; ci < cinfo->num_components; ci++) {
	219	int row;
	220	for (row = 1; row <= cinfo->max_v_samp_factor; row++) {
	221	jcopy_sample_rows(prep->color_buf[ci], 0,
	222	prep->color_buf[ci], -row,
	223	1, cinfo->image_width);
	224	}
	225	}
	226	}
	227	*in_row_ctr += numrows;
	228	prep->next_buf_row += numrows;
	229	prep->rows_to_go -= numrows;
	230	} else {
	231	/* Return for more data, unless we are at the bottom of the image. */
	232	if (prep->rows_to_go != 0)
	233	break;
	234	/* When at bottom of image, pad to fill the conversion buffer. */
	235	if (prep->next_buf_row < prep->next_buf_stop) {
	236	for (ci = 0; ci < cinfo->num_components; ci++) {
	237	expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
	238	prep->next_buf_row, prep->next_buf_stop);
	239	}
	240	prep->next_buf_row = prep->next_buf_stop;
	241	}
	242	}
	243	/* If we've gotten enough data, downsample a row group. */
	244	if (prep->next_buf_row == prep->next_buf_stop) {
	245	(*cinfo->downsample->downsample) (cinfo,
	246	prep->color_buf,
	247	(JDIMENSION) prep->this_row_group,
	248	output_buf, *out_row_group_ctr);
	249	(*out_row_group_ctr)++;
	250	/* Advance pointers with wraparound as necessary. */
	251	prep->this_row_group += cinfo->max_v_samp_factor;
	252	if (prep->this_row_group >= buf_height)
	253	prep->this_row_group = 0;
	254	if (prep->next_buf_row >= buf_height)
	255	prep->next_buf_row = 0;
	256	prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor;
	257	}
	258	}
	259	}
	260
	261
	262	/*
	263	* Create the wrapped-around downsampling input buffer needed for context mode.
	264	*/
	265
	266	LOCAL(void)
	267	create_context_buffer (j_compress_ptr cinfo)
	268	{
	269	my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
	270	int rgroup_height = cinfo->max_v_samp_factor;
	271	int ci, i;
	272	jpeg_component_info * compptr;
	273	JSAMPARRAY true_buffer, fake_buffer;
	274
	275	/* Grab enough space for fake row pointers for all the components;
	276	* we need five row groups' worth of pointers for each component.
	277	*/
	278	fake_buffer = (JSAMPARRAY)
	279	(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
	280	(cinfo->num_components * 5 * rgroup_height) *
	281	SIZEOF(JSAMPROW));
	282
	283	for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
	284	ci++, compptr++) {
	285	/* Allocate the actual buffer space (3 row groups) for this component.
	286	* We make the buffer wide enough to allow the downsampler to edge-expand
	287	* horizontally within the buffer, if it so chooses.
	288	*/
	289	true_buffer = (*cinfo->mem->alloc_sarray)
	290	((j_common_ptr) cinfo, JPOOL_IMAGE,
	291	(JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
	292	cinfo->max_h_samp_factor) / compptr->h_samp_factor),
	293	(JDIMENSION) (3 * rgroup_height));
	294	/* Copy true buffer row pointers into the middle of the fake row array */
	295	MEMCOPY(fake_buffer + rgroup_height, true_buffer,
	296	3 * rgroup_height * SIZEOF(JSAMPROW));
	297	/* Fill in the above and below wraparound pointers */
	298	for (i = 0; i < rgroup_height; i++) {
	299	fake_buffer[i] = true_buffer[2 * rgroup_height + i];
	300	fake_buffer[4 * rgroup_height + i] = true_buffer[i];
	301	}
	302	prep->color_buf[ci] = fake_buffer + rgroup_height;
	303	fake_buffer += 5 * rgroup_height; /* point to space for next component */
	304	}
	305	}
	306
	307	#endif /* CONTEXT_ROWS_SUPPORTED */
	308
	309
	310	/*
	311	* Initialize preprocessing controller.
	312	*/
	313
	314	GLOBAL(void)
	315	jinit_c_prep_controller (j_compress_ptr cinfo, boolean need_full_buffer)
	316	{
	317	my_prep_ptr prep;
	318	int ci;
	319	jpeg_component_info * compptr;
	320
	321	if (need_full_buffer) /* safety check */
	322	ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
	323
	324	prep = (my_prep_ptr)
	325	(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
	326	SIZEOF(my_prep_controller));
	327	cinfo->prep = (struct jpeg_c_prep_controller *) prep;
	328	prep->pub.start_pass = start_pass_prep;
	329
	330	/* Allocate the color conversion buffer.
	331	* We make the buffer wide enough to allow the downsampler to edge-expand
	332	* horizontally within the buffer, if it so chooses.
	333	*/
	334	if (cinfo->downsample->need_context_rows) {
	335	/* Set up to provide context rows */
	336	#ifdef CONTEXT_ROWS_SUPPORTED
	337	prep->pub.pre_process_data = pre_process_context;
	338	create_context_buffer(cinfo);
	339	#else
	340	ERREXIT(cinfo, JERR_NOT_COMPILED);
	341	#endif
	342	} else {
	343	/* No context, just make it tall enough for one row group */
	344	prep->pub.pre_process_data = pre_process_data;
	345	for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
	346	ci++, compptr++) {
	347	prep->color_buf[ci] = (*cinfo->mem->alloc_sarray)
	348	((j_common_ptr) cinfo, JPOOL_IMAGE,
	349	(JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
	350	cinfo->max_h_samp_factor) / compptr->h_samp_factor),
	351	(JDIMENSION) cinfo->max_v_samp_factor);
	352	}
	353	}
	354	}