jccoefct.c

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/*
 * jccoefct.c
 *
 * Copyright (C) 1994-1997, Thomas G. Lane.
 * Modified 2003-2022 by Guido Vollbeding.
 * 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 coefficient buffer controller for compression.
 * This controller is the top level of the JPEG compressor proper.
 * The coefficient buffer lies between forward-DCT and entropy encoding steps.
 */
 
#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
 
 
/* We use a full-image coefficient buffer when doing Huffman optimization,
 * and also for writing multiple-scan JPEG files.  In all cases, the DCT
 * step is run during the first pass, and subsequent passes need only read
 * the buffered coefficients.
 */
#ifdef ENTROPY_OPT_SUPPORTED
#define FULL_COEF_BUFFER_SUPPORTED
#else
#ifdef C_MULTISCAN_FILES_SUPPORTED
#define FULL_COEF_BUFFER_SUPPORTED
#endif
#endif
 
 
/* Private buffer controller object */
 
typedef struct {
  struct jpeg_c_coef_controller pub; /* public fields */
 
  JDIMENSION iMCU_row_num;  /* iMCU row # within image */
  JDIMENSION MCU_ctr;       /* counts MCUs processed in current row */
  int MCU_vert_offset;      /* counts MCU rows within iMCU row */
  int MCU_rows_per_iMCU_row;    /* number of such rows needed */
 
  /* For single-pass compression, it's sufficient to buffer just one MCU
   * (although this may prove a bit slow in practice).
   * We append a workspace of C_MAX_BLOCKS_IN_MCU coefficient blocks,
   * and reuse it for each MCU constructed and sent.
   * In multi-pass modes, this array points to the current MCU's blocks
   * within the virtual arrays.
   */
  JBLOCKROW MCU_buffer[C_MAX_BLOCKS_IN_MCU];
 
  /* In multi-pass modes, we need a virtual block array for each component. */
  jvirt_barray_ptr whole_image[MAX_COMPONENTS];
 
  /* Workspace for single-pass compression (omitted otherwise). */
  JBLOCK blk_buffer[C_MAX_BLOCKS_IN_MCU];
} my_coef_controller;
 
typedef my_coef_controller * my_coef_ptr;
 
 
/* Forward declarations */
METHODDEF(boolean) compress_data
    JPP((j_compress_ptr cinfo, JSAMPIMAGE input_buf));
#ifdef FULL_COEF_BUFFER_SUPPORTED
METHODDEF(boolean) compress_first_pass
    JPP((j_compress_ptr cinfo, JSAMPIMAGE input_buf));
METHODDEF(boolean) compress_output
    JPP((j_compress_ptr cinfo, JSAMPIMAGE input_buf));
#endif
 
 
LOCAL(void)
start_iMCU_row (j_compress_ptr cinfo)
/* Reset within-iMCU-row counters for a new row */
{
  my_coef_ptr coef = (my_coef_ptr) cinfo->coef;
 
  /* In an interleaved scan, an MCU row is the same as an iMCU row.
   * In a noninterleaved scan, an iMCU row has v_samp_factor MCU rows.
   * But at the bottom of the image, process only what's left.
   */
  if (cinfo->comps_in_scan > 1) {
    coef->MCU_rows_per_iMCU_row = 1;
  } else {
    if (coef->iMCU_row_num < (cinfo->total_iMCU_rows-1))
      coef->MCU_rows_per_iMCU_row = cinfo->cur_comp_info[0]->v_samp_factor;
    else
      coef->MCU_rows_per_iMCU_row = cinfo->cur_comp_info[0]->last_row_height;
  }
 
  coef->MCU_ctr = 0;
  coef->MCU_vert_offset = 0;
}
 
 
/*
 * Initialize for a processing pass.
 */
 
METHODDEF(void)
start_pass_coef (j_compress_ptr cinfo, J_BUF_MODE pass_mode)
{
  my_coef_ptr coef = (my_coef_ptr) cinfo->coef;
 
  coef->iMCU_row_num = 0;
  start_iMCU_row(cinfo);
 
  switch (pass_mode) {
  case JBUF_PASS_THRU:
    if (coef->whole_image[0] != NULL)
      ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
    coef->pub.compress_data = compress_data;
    break;
#ifdef FULL_COEF_BUFFER_SUPPORTED
  case JBUF_SAVE_AND_PASS:
    if (coef->whole_image[0] == NULL)
      ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
    coef->pub.compress_data = compress_first_pass;
    break;
  case JBUF_CRANK_DEST:
    if (coef->whole_image[0] == NULL)
      ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
    coef->pub.compress_data = compress_output;
    break;
#endif
  default:
    ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
  }
}
 
 
/*
 * Process some data in the single-pass case.
 * We process the equivalent of one fully interleaved MCU row ("iMCU" row)
 * per call, ie, v_samp_factor block rows for each component in the image.
 * Returns TRUE if the iMCU row is completed, FALSE if suspended.
 *
 * NB: input_buf contains a plane for each component in image,
 * which we index according to the component's SOF position.
 */
 
METHODDEF(boolean)
compress_data (j_compress_ptr cinfo, JSAMPIMAGE input_buf)
{
  my_coef_ptr coef = (my_coef_ptr) cinfo->coef;
  JDIMENSION MCU_col_num;   /* index of current MCU within row */
  JDIMENSION last_MCU_col = cinfo->MCUs_per_row - 1;
  JDIMENSION last_iMCU_row = cinfo->total_iMCU_rows - 1;
  int ci, xindex, yindex, yoffset, blockcnt;
  JBLOCKROW blkp;
  JSAMPARRAY input_ptr;
  JDIMENSION xpos;
  jpeg_component_info *compptr;
  forward_DCT_ptr forward_DCT;
 
  /* Loop to write as much as one whole iMCU row */
  for (yoffset = coef->MCU_vert_offset; yoffset < coef->MCU_rows_per_iMCU_row;
       yoffset++) {
    for (MCU_col_num = coef->MCU_ctr; MCU_col_num <= last_MCU_col;
     MCU_col_num++) {
      /* Determine where data comes from in input_buf and do the DCT thing.
       * Each call on forward_DCT processes a horizontal row of DCT blocks as
       * wide as an MCU.  Dummy blocks at the right or bottom edge are filled in
       * specially.  The data in them does not matter for image reconstruction,
       * so we fill them with values that will encode to the smallest amount of
       * data, viz: all zeroes in the AC entries, DC entries equal to previous
       * block's DC value.  (Thanks to Thomas Kinsman for this idea.)
       */
      blkp = coef->blk_buffer;  /* pointer to current DCT block within MCU */
      for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
    compptr = cinfo->cur_comp_info[ci];
    forward_DCT = cinfo->fdct->forward_DCT[compptr->component_index];
    input_ptr = input_buf[compptr->component_index] +
      yoffset * compptr->DCT_v_scaled_size;
    /* ypos == (yoffset + yindex) * compptr->DCT_v_scaled_size */
    blockcnt = (MCU_col_num < last_MCU_col) ? compptr->MCU_width
                        : compptr->last_col_width;
    xpos = MCU_col_num * compptr->MCU_sample_width;
    for (yindex = 0; yindex < compptr->MCU_height; yindex++) {
      if (coef->iMCU_row_num < last_iMCU_row ||
          yoffset + yindex < compptr->last_row_height) {
        (*forward_DCT) (cinfo, compptr, input_ptr, blkp,
                xpos, (JDIMENSION) blockcnt);
        input_ptr += compptr->DCT_v_scaled_size;
        blkp += blockcnt;
        /* Dummy blocks at right edge */
        if ((xindex = compptr->MCU_width - blockcnt) == 0)
          continue;
      } else {
        /* At bottom of image, need a whole row of dummy blocks */
        xindex = compptr->MCU_width;
      }
      /* Fill in any dummy blocks needed in this row */
      MEMZERO(blkp, xindex * SIZEOF(JBLOCK));
      do {
        blkp[0][0] = blkp[-1][0];
        blkp++;
      } while (--xindex);
    }
      }
      /* Try to write the MCU.  In event of a suspension failure, we will
       * re-DCT the MCU on restart (a bit inefficient, could be fixed...)
       */
      if (! (*cinfo->entropy->encode_mcu) (cinfo, coef->MCU_buffer)) {
    /* Suspension forced; update state counters and exit */
    coef->MCU_vert_offset = yoffset;
    coef->MCU_ctr = MCU_col_num;
    return FALSE;
      }
    }
    /* Completed an MCU row, but perhaps not an iMCU row */
    coef->MCU_ctr = 0;
  }
  /* Completed the iMCU row, advance counters for next one */
  coef->iMCU_row_num++;
  start_iMCU_row(cinfo);
  return TRUE;
}
 
 
#ifdef FULL_COEF_BUFFER_SUPPORTED
 
/*
 * Process some data in the first pass of a multi-pass case.
 * We process the equivalent of one fully interleaved MCU row ("iMCU" row)
 * per call, ie, v_samp_factor block rows for each component in the image.
 * This amount of data is read from the source buffer, DCT'd and quantized,
 * and saved into the virtual arrays.  We also generate suitable dummy blocks
 * as needed at the right and lower edges.  (The dummy blocks are constructed
 * in the virtual arrays, which have been padded appropriately.)  This makes
 * it possible for subsequent passes not to worry about real vs. dummy blocks.
 *
 * We must also emit the data to the entropy encoder.  This is conveniently
 * done by calling compress_output() after we've loaded the current strip
 * of the virtual arrays.
 *
 * NB: input_buf contains a plane for each component in image.  All
 * components are DCT'd and loaded into the virtual arrays in this pass.
 * However, it may be that only a subset of the components are emitted to
 * the entropy encoder during this first pass; be careful about looking
 * at the scan-dependent variables (MCU dimensions, etc).
 */
 
METHODDEF(boolean)
compress_first_pass (j_compress_ptr cinfo, JSAMPIMAGE input_buf)
{
  my_coef_ptr coef = (my_coef_ptr) cinfo->coef;
  JDIMENSION last_iMCU_row = cinfo->total_iMCU_rows - 1;
  JDIMENSION blocks_across, MCUs_across, MCUindex;
  int bi, ci, h_samp_factor, block_row, block_rows, ndummy;
  JCOEF lastDC;
  jpeg_component_info *compptr;
  JBLOCKARRAY buffer;
  JBLOCKROW thisblockrow, lastblockrow;
  JSAMPARRAY input_ptr;
  forward_DCT_ptr forward_DCT;
 
  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
       ci++, compptr++) {
    /* Align the virtual buffer for this component. */
    buffer = (*cinfo->mem->access_virt_barray)
      ((j_common_ptr) cinfo, coef->whole_image[ci],
       coef->iMCU_row_num * compptr->v_samp_factor,
       (JDIMENSION) compptr->v_samp_factor, TRUE);
    /* Count non-dummy DCT block rows in this iMCU row. */
    if (coef->iMCU_row_num < last_iMCU_row)
      block_rows = compptr->v_samp_factor;
    else {
      /* NB: can't use last_row_height here, since may not be set! */
      block_rows = (int) (compptr->height_in_blocks % compptr->v_samp_factor);
      if (block_rows == 0) block_rows = compptr->v_samp_factor;
    }
    blocks_across = compptr->width_in_blocks;
    h_samp_factor = compptr->h_samp_factor;
    /* Count number of dummy blocks to be added at the right margin. */
    ndummy = (int) (blocks_across % h_samp_factor);
    if (ndummy > 0)
      ndummy = h_samp_factor - ndummy;
    forward_DCT = cinfo->fdct->forward_DCT[ci];
    input_ptr = input_buf[ci];
    /* Perform DCT for all non-dummy blocks in this iMCU row.  Each call
     * on forward_DCT processes a complete horizontal row of DCT blocks.
     */
    for (block_row = 0; block_row < block_rows; block_row++) {
      thisblockrow = buffer[block_row];
      (*forward_DCT) (cinfo, compptr, input_ptr, thisblockrow,
              (JDIMENSION) 0, blocks_across);
      input_ptr += compptr->DCT_v_scaled_size;
      if (ndummy > 0) {
    /* Create dummy blocks at the right edge of the image. */
    thisblockrow += blocks_across; /* => first dummy block */
    FMEMZERO((void FAR *) thisblockrow, ndummy * SIZEOF(JBLOCK));
    lastDC = thisblockrow[-1][0];
    for (bi = 0; bi < ndummy; bi++) {
      thisblockrow[bi][0] = lastDC;
    }
      }
    }
    /* If at end of image, create dummy block rows as needed.
     * The tricky part here is that within each MCU, we want the DC values
     * of the dummy blocks to match the last real block's DC value.
     * This squeezes a few more bytes out of the resulting file...
     */
    if (block_row < compptr->v_samp_factor) {
      blocks_across += ndummy;  /* include lower right corner */
      MCUs_across = blocks_across / h_samp_factor;
      do {
    thisblockrow = buffer[block_row];
    lastblockrow = buffer[block_row-1];
    FMEMZERO((void FAR *) thisblockrow,
         (size_t) blocks_across * SIZEOF(JBLOCK));
    for (MCUindex = 0; MCUindex < MCUs_across; MCUindex++) {
      lastDC = lastblockrow[h_samp_factor-1][0];
      for (bi = 0; bi < h_samp_factor; bi++) {
        thisblockrow[bi][0] = lastDC;
      }
      thisblockrow += h_samp_factor; /* advance to next MCU in row */
      lastblockrow += h_samp_factor;
    }
      } while (++block_row < compptr->v_samp_factor);
    }
  }
  /* NB: compress_output will increment iMCU_row_num if successful.
   * A suspension return will result in redoing all the work above next time.
   */
 
  /* Emit data to the entropy encoder, sharing code with subsequent passes */
  return compress_output(cinfo, input_buf);
}
 
 
/*
 * Process some data in subsequent passes of a multi-pass case.
 * We process the equivalent of one fully interleaved MCU row ("iMCU" row)
 * per call, ie, v_samp_factor block rows for each component in the scan.
 * The data is obtained from the virtual arrays and fed to the entropy coder.
 * Returns TRUE if the iMCU row is completed, FALSE if suspended.
 *
 * NB: input_buf is ignored; it is likely to be a NULL pointer.
 */
 
METHODDEF(boolean)
compress_output (j_compress_ptr cinfo, JSAMPIMAGE input_buf)
{
  my_coef_ptr coef = (my_coef_ptr) cinfo->coef;
  JDIMENSION MCU_col_num;   /* index of current MCU within row */
  int ci, xindex, yindex, yoffset;
  JDIMENSION start_col;
  JBLOCKARRAY blkp;
  JBLOCKARRAY buffer[MAX_COMPS_IN_SCAN];
  JBLOCKROW buffer_ptr;
  jpeg_component_info *compptr;
 
  /* Align the virtual buffers for the components used in this scan.
   * NB: during first pass, this is safe only because the buffers will
   * already be aligned properly, so jmemmgr.c won't need to do any I/O.
   */
  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
    compptr = cinfo->cur_comp_info[ci];
    buffer[ci] = (*cinfo->mem->access_virt_barray)
      ((j_common_ptr) cinfo, coef->whole_image[compptr->component_index],
       coef->iMCU_row_num * compptr->v_samp_factor,
       (JDIMENSION) compptr->v_samp_factor, FALSE);
  }
 
  /* Loop to process one whole iMCU row */
  for (yoffset = coef->MCU_vert_offset; yoffset < coef->MCU_rows_per_iMCU_row;
       yoffset++) {
    for (MCU_col_num = coef->MCU_ctr; MCU_col_num < cinfo->MCUs_per_row;
     MCU_col_num++) {
      /* Construct list of pointers to DCT blocks belonging to this MCU */
      blkp = coef->MCU_buffer;  /* pointer to current DCT block within MCU */
      for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
    compptr = cinfo->cur_comp_info[ci];
    start_col = MCU_col_num * compptr->MCU_width;
    for (yindex = 0; yindex < compptr->MCU_height; yindex++) {
      buffer_ptr = buffer[ci][yoffset + yindex] + start_col;
      xindex = compptr->MCU_width;
      do {
        *blkp++ = buffer_ptr++;
      } while (--xindex);
    }
      }
      /* Try to write the MCU. */
      if (! (*cinfo->entropy->encode_mcu) (cinfo, coef->MCU_buffer)) {
    /* Suspension forced; update state counters and exit */
    coef->MCU_vert_offset = yoffset;
    coef->MCU_ctr = MCU_col_num;
    return FALSE;
      }
    }
    /* Completed an MCU row, but perhaps not an iMCU row */
    coef->MCU_ctr = 0;
  }
  /* Completed the iMCU row, advance counters for next one */
  coef->iMCU_row_num++;
  start_iMCU_row(cinfo);
  return TRUE;
}
 
#endif /* FULL_COEF_BUFFER_SUPPORTED */
 
 
/*
 * Initialize coefficient buffer controller.
 */
 
GLOBAL(void)
jinit_c_coef_controller (j_compress_ptr cinfo, boolean need_full_buffer)
{
  my_coef_ptr coef;
 
  if (need_full_buffer) {
#ifdef FULL_COEF_BUFFER_SUPPORTED
    /* Allocate a full-image virtual array for each component, */
    /* padded to a multiple of samp_factor DCT blocks in each direction. */
    int ci;
    jpeg_component_info *compptr;
 
    coef = (my_coef_ptr) (*cinfo->mem->alloc_small)
      ((j_common_ptr) cinfo, JPOOL_IMAGE,
       SIZEOF(my_coef_controller) - SIZEOF(coef->blk_buffer));
    for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
     ci++, compptr++) {
      coef->whole_image[ci] = (*cinfo->mem->request_virt_barray)
    ((j_common_ptr) cinfo, JPOOL_IMAGE, FALSE,
     (JDIMENSION) jround_up((long) compptr->width_in_blocks,
                (long) compptr->h_samp_factor),
     (JDIMENSION) jround_up((long) compptr->height_in_blocks,
                (long) compptr->v_samp_factor),
     (JDIMENSION) compptr->v_samp_factor);
    }
#else
    ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
#endif
  } else {
    /* We only need a single-MCU buffer. */
    JBLOCKARRAY blkp;
    JBLOCKROW buffer_ptr;
    int bi;
 
    coef = (my_coef_ptr) (*cinfo->mem->alloc_small)
      ((j_common_ptr) cinfo, JPOOL_IMAGE, SIZEOF(my_coef_controller));
    blkp = coef->MCU_buffer;
    buffer_ptr = coef->blk_buffer;
    bi = C_MAX_BLOCKS_IN_MCU;
    do {
      *blkp++ = buffer_ptr++;
    } while (--bi);
    coef->whole_image[0] = NULL; /* flag for no virtual arrays */
  }
 
  coef->pub.start_pass = start_pass_coef;
  cinfo->coef = &coef->pub;
}