tor-browser

jcprepct.c (13564B)

---

/*
* jcprepct.c
*
* This file was part of the Independent JPEG Group's software:
* Copyright (C) 1994-1996, Thomas G. Lane.
* Lossless JPEG Modifications:
* Copyright (C) 1999, Ken Murchison.
* 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"
#include "jsamplecomp.h"


#if BITS_IN_JSAMPLE != 16 || defined(C_LOSSLESS_SUPPORTED)

/* 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;
 int data_unit = cinfo->master->lossless ? 1 : DCTSIZE;

 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 * data_unit,
                          (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;
 int data_unit = cinfo->master->lossless ? 1 : DCTSIZE;

 /* 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 = (_JSAMPARRAY)(*cinfo->mem->alloc_sarray)
     ((j_common_ptr)cinfo, JPOOL_IMAGE,
      (JDIMENSION)(((long)compptr->width_in_blocks * data_unit *
                    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 */
   memcpy(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;
 int data_unit = cinfo->master->lossless ? 1 : DCTSIZE;

 if (cinfo->data_precision != BITS_IN_JSAMPLE)
   ERREXIT1(cinfo, JERR_BAD_PRECISION, cinfo->data_precision);

 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] = (_JSAMPARRAY)(*cinfo->mem->alloc_sarray)
       ((j_common_ptr)cinfo, JPOOL_IMAGE,
        (JDIMENSION)(((long)compptr->width_in_blocks * data_unit *
                      cinfo->max_h_samp_factor) / compptr->h_samp_factor),
        (JDIMENSION)cinfo->max_v_samp_factor);
   }
 }
}

#endif /* BITS_IN_JSAMPLE != 16 || defined(C_LOSSLESS_SUPPORTED) */