jdapistd.c

/*
 * jdapistd.c
 *
 * This file was part of the Independent JPEG Group's software:
 * Copyright (C) 1994-1996, Thomas G. Lane.
 * libjpeg-turbo Modifications:
 * Copyright (C) 2010, 2015, D. R. Commander.
 * Copyright (C) 2015, Google, Inc.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains application interface code for the decompression half
 * of the JPEG library.  These are the "standard" API routines that are
 * used in the normal full-decompression case.  They are not used by a
 * transcoding-only application.  Note that if an application links in
 * jpeg_start_decompress, it will end up linking in the entire decompressor.
 * We thus must separate this file from jdapimin.c to avoid linking the
 * whole decompression library into a transcoder.
 */

#include "jdmainct.h"
#include "jdcoefct.h"
#include "jdsample.h"
#include "jmemsys.h"

/* Forward declarations */
LOCAL(boolean) output_pass_setup (j_decompress_ptr cinfo);


/*
 * Decompression initialization.
 * jpeg_read_header must be completed before calling this.
 *
 * If a multipass operating mode was selected, this will do all but the
 * last pass, and thus may take a great deal of time.
 *
 * Returns FALSE if suspended.  The return value need be inspected only if
 * a suspending data source is used.
 */

GLOBAL(boolean)
jpeg_start_decompress (j_decompress_ptr cinfo)
{
  if (cinfo->global_state == DSTATE_READY) {
    /* First call: initialize master control, select active modules */
    jinit_master_decompress(cinfo);
    if (cinfo->buffered_image) {
      /* No more work here; expecting jpeg_start_output next */
      cinfo->global_state = DSTATE_BUFIMAGE;
      return TRUE;
    }
    cinfo->global_state = DSTATE_PRELOAD;
  }
  if (cinfo->global_state == DSTATE_PRELOAD) {
    /* If file has multiple scans, absorb them all into the coef buffer */
    if (cinfo->inputctl->has_multiple_scans) {
#ifdef D_MULTISCAN_FILES_SUPPORTED
      for (;;) {
        int retcode;
        /* Call progress monitor hook if present */
        if (cinfo->progress != NULL)
          (*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo);
        /* Absorb some more input */
        retcode = (*cinfo->inputctl->consume_input) (cinfo);
        if (retcode == JPEG_SUSPENDED)
          return FALSE;
        if (retcode == JPEG_REACHED_EOI)
          break;
        /* Advance progress counter if appropriate */
        if (cinfo->progress != NULL &&
            (retcode == JPEG_ROW_COMPLETED || retcode == JPEG_REACHED_SOS)) {
          if (++cinfo->progress->pass_counter >= cinfo->progress->pass_limit) {
            /* jdmaster underestimated number of scans; ratchet up one scan */
            cinfo->progress->pass_limit += (long) cinfo->total_iMCU_rows;
          }
        }
      }
#else
      ERREXIT(cinfo, JERR_NOT_COMPILED);
#endif /* D_MULTISCAN_FILES_SUPPORTED */
    }
    cinfo->output_scan_number = cinfo->input_scan_number;
  } else if (cinfo->global_state != DSTATE_PRESCAN)
    ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
  /* Perform any dummy output passes, and set up for the final pass */
  return output_pass_setup(cinfo);
}


/*
 * Set up for an output pass, and perform any dummy pass(es) needed.
 * Common subroutine for jpeg_start_decompress and jpeg_start_output.
 * Entry: global_state = DSTATE_PRESCAN only if previously suspended.
 * Exit: If done, returns TRUE and sets global_state for proper output mode.
 *       If suspended, returns FALSE and sets global_state = DSTATE_PRESCAN.
 */

LOCAL(boolean)
output_pass_setup (j_decompress_ptr cinfo)
{
  if (cinfo->global_state != DSTATE_PRESCAN) {
    /* First call: do pass setup */
    (*cinfo->master->prepare_for_output_pass) (cinfo);
    cinfo->output_scanline = 0;
    cinfo->global_state = DSTATE_PRESCAN;
  }
  /* Loop over any required dummy passes */
  while (cinfo->master->is_dummy_pass) {
#ifdef QUANT_2PASS_SUPPORTED
    /* Crank through the dummy pass */
    while (cinfo->output_scanline < cinfo->output_height) {
      JDIMENSION last_scanline;
      /* Call progress monitor hook if present */
      if (cinfo->progress != NULL) {
        cinfo->progress->pass_counter = (long) cinfo->output_scanline;
        cinfo->progress->pass_limit = (long) cinfo->output_height;
        (*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo);
      }
      /* Process some data */
      last_scanline = cinfo->output_scanline;
      (*cinfo->main->process_data) (cinfo, (JSAMPARRAY) NULL,
                                    &cinfo->output_scanline, (JDIMENSION) 0);
      if (cinfo->output_scanline == last_scanline)
        return FALSE;           /* No progress made, must suspend */
    }
    /* Finish up dummy pass, and set up for another one */
    (*cinfo->master->finish_output_pass) (cinfo);
    (*cinfo->master->prepare_for_output_pass) (cinfo);
    cinfo->output_scanline = 0;
#else
    ERREXIT(cinfo, JERR_NOT_COMPILED);
#endif /* QUANT_2PASS_SUPPORTED */
  }
  /* Ready for application to drive output pass through
   * jpeg_read_scanlines or jpeg_read_raw_data.
   */
  cinfo->global_state = cinfo->raw_data_out ? DSTATE_RAW_OK : DSTATE_SCANNING;
  return TRUE;
}


/*
 * Read some scanlines of data from the JPEG decompressor.
 *
 * The return value will be the number of lines actually read.
 * This may be less than the number requested in several cases,
 * including bottom of image, data source suspension, and operating
 * modes that emit multiple scanlines at a time.
 *
 * Note: we warn about excess calls to jpeg_read_scanlines() since
 * this likely signals an application programmer error.  However,
 * an oversize buffer (max_lines > scanlines remaining) is not an error.
 */

GLOBAL(JDIMENSION)
jpeg_read_scanlines (j_decompress_ptr cinfo, JSAMPARRAY scanlines,
                     JDIMENSION max_lines)
{
  JDIMENSION row_ctr;

  if (cinfo->global_state != DSTATE_SCANNING)
    ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
  if (cinfo->output_scanline >= cinfo->output_height) {
    WARNMS(cinfo, JWRN_TOO_MUCH_DATA);
    return 0;
  }

  /* Call progress monitor hook if present */
  if (cinfo->progress != NULL) {
    cinfo->progress->pass_counter = (long) cinfo->output_scanline;
    cinfo->progress->pass_limit = (long) cinfo->output_height;
    (*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo);
  }

  /* Process some data */
  row_ctr = 0;
  (*cinfo->main->process_data) (cinfo, scanlines, &row_ctr, max_lines);
  cinfo->output_scanline += row_ctr;
  return row_ctr;
}


/* Dummy color convert function used by jpeg_skip_scanlines() */
LOCAL(void)
noop_convert (j_decompress_ptr cinfo, JSAMPIMAGE input_buf,
              JDIMENSION input_row, JSAMPARRAY output_buf, int num_rows)
{
}


/*
 * In some cases, it is best to call jpeg_read_scanlines() and discard the
 * output, rather than skipping the scanlines, because this allows us to
 * maintain the internal state of the context-based upsampler.  In these cases,
 * we set up and tear down a dummy color converter in order to avoid valgrind
 * errors and to achieve the best possible performance.
 */

LOCAL(void)
read_and_discard_scanlines (j_decompress_ptr cinfo, JDIMENSION num_lines)
{
  JDIMENSION n;
  void (*color_convert) (j_decompress_ptr cinfo, JSAMPIMAGE input_buf,
                         JDIMENSION input_row, JSAMPARRAY output_buf,
                         int num_rows);

  color_convert = cinfo->cconvert->color_convert;
  cinfo->cconvert->color_convert = noop_convert;

  for (n = 0; n < num_lines; n++)
    jpeg_read_scanlines(cinfo, NULL, 1);

  cinfo->cconvert->color_convert = color_convert;
}


/*
 * Called by jpeg_skip_scanlines().  This partially skips a decompress block by
 * incrementing the rowgroup counter.
 */

LOCAL(void)
increment_simple_rowgroup_ctr (j_decompress_ptr cinfo, JDIMENSION rows)
{
  JDIMENSION rows_left;
  my_main_ptr main_ptr = (my_main_ptr) cinfo->main;

  /* Increment the counter to the next row group after the skipped rows. */
  main_ptr->rowgroup_ctr += rows / cinfo->max_v_samp_factor;

  /* Partially skipping a row group would involve modifying the internal state
   * of the upsampler, so read the remaining rows into a dummy buffer instead.
   */
  rows_left = rows % cinfo->max_v_samp_factor;
  cinfo->output_scanline += rows - rows_left;

  read_and_discard_scanlines(cinfo, rows_left);
}

/*
 * Skips some scanlines of data from the JPEG decompressor.
 *
 * The return value will be the number of lines actually skipped.  If skipping
 * num_lines would move beyond the end of the image, then the actual number of
 * lines remaining in the image is returned.  Otherwise, the return value will
 * be equal to num_lines.
 *
 * Refer to libjpeg.txt for more information.
 */

GLOBAL(JDIMENSION)
jpeg_skip_scanlines (j_decompress_ptr cinfo, JDIMENSION num_lines)
{
  my_main_ptr main_ptr = (my_main_ptr) cinfo->main;
  my_coef_ptr coef = (my_coef_ptr) cinfo->coef;
  my_upsample_ptr upsample = (my_upsample_ptr) cinfo->upsample;
  JDIMENSION i, x;
  int y;
  JDIMENSION lines_per_iMCU_row, lines_left_in_iMCU_row, lines_after_iMCU_row;
  JDIMENSION lines_to_skip, lines_to_read;

  if (cinfo->global_state != DSTATE_SCANNING)
    ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);

  /* Do not skip past the bottom of the image. */
  if (cinfo->output_scanline + num_lines >= cinfo->output_height) {
    cinfo->output_scanline = cinfo->output_height;
    return cinfo->output_height - cinfo->output_scanline;
  }

  if (num_lines == 0)
    return 0;

  lines_per_iMCU_row = cinfo->_min_DCT_scaled_size * cinfo->max_v_samp_factor;
  lines_left_in_iMCU_row =
    (lines_per_iMCU_row - (cinfo->output_scanline % lines_per_iMCU_row)) %
    lines_per_iMCU_row;
  lines_after_iMCU_row = num_lines - lines_left_in_iMCU_row;

  /* Skip the lines remaining in the current iMCU row.  When upsampling
   * requires context rows, we need the previous and next rows in order to read
   * the current row.  This adds some complexity.
   */
  if (cinfo->upsample->need_context_rows) {
    /* If the skipped lines would not move us past the current iMCU row, we
     * read the lines and ignore them.  There might be a faster way of doing
     * this, but we are facing increasing complexity for diminishing returns.
     * The increasing complexity would be a by-product of meddling with the
     * state machine used to skip context rows.  Near the end of an iMCU row,
     * the next iMCU row may have already been entropy-decoded.  In this unique
     * case, we will read the next iMCU row if we cannot skip past it as well.
     */
    if ((num_lines < lines_left_in_iMCU_row + 1) ||
        (lines_left_in_iMCU_row <= 1 && main_ptr->buffer_full &&
         lines_after_iMCU_row < lines_per_iMCU_row + 1)) {
      read_and_discard_scanlines(cinfo, num_lines);
      return num_lines;
    }

    /* If the next iMCU row has already been entropy-decoded, make sure that
     * we do not skip too far.
     */
    if (lines_left_in_iMCU_row <= 1 && main_ptr->buffer_full) {
      cinfo->output_scanline += lines_left_in_iMCU_row + lines_per_iMCU_row;
      lines_after_iMCU_row -= lines_per_iMCU_row;
    } else {
      cinfo->output_scanline += lines_left_in_iMCU_row;
    }

    /* If we have just completed the first block, adjust the buffer pointers */
    if (main_ptr->iMCU_row_ctr == 0 ||
        (main_ptr->iMCU_row_ctr == 1 && lines_left_in_iMCU_row > 2))
      set_wraparound_pointers(cinfo);
    main_ptr->buffer_full = FALSE;
    main_ptr->rowgroup_ctr = 0;
    main_ptr->context_state = CTX_PREPARE_FOR_IMCU;
    upsample->next_row_out = cinfo->max_v_samp_factor;
    upsample->rows_to_go = cinfo->output_height - cinfo->output_scanline;
  }

  /* Skipping is much simpler when context rows are not required. */
  else {
    if (num_lines < lines_left_in_iMCU_row) {
      increment_simple_rowgroup_ctr(cinfo, num_lines);
      return num_lines;
    } else {
      cinfo->output_scanline += lines_left_in_iMCU_row;
      main_ptr->buffer_full = FALSE;
      main_ptr->rowgroup_ctr = 0;
      upsample->next_row_out = cinfo->max_v_samp_factor;
      upsample->rows_to_go = cinfo->output_height - cinfo->output_scanline;
    }
  }

  /* Calculate how many full iMCU rows we can skip. */
  if (cinfo->upsample->need_context_rows)
    lines_to_skip = ((lines_after_iMCU_row - 1) / lines_per_iMCU_row) *
                    lines_per_iMCU_row;
  else
    lines_to_skip = (lines_after_iMCU_row / lines_per_iMCU_row) *
                    lines_per_iMCU_row;
  /* Calculate the number of lines that remain to be skipped after skipping all
   * of the full iMCU rows that we can.  We will not read these lines unless we
   * have to.
   */
  lines_to_read = lines_after_iMCU_row - lines_to_skip;

  /* For images requiring multiple scans (progressive, non-interleaved, etc.),
   * all of the entropy decoding occurs in jpeg_start_decompress(), assuming
   * that the input data source is non-suspending.  This makes skipping easy.
   */
  if (cinfo->inputctl->has_multiple_scans) {
    if (cinfo->upsample->need_context_rows) {
      cinfo->output_scanline += lines_to_skip;
      cinfo->output_iMCU_row += lines_to_skip / lines_per_iMCU_row;
      main_ptr->iMCU_row_ctr += lines_after_iMCU_row / lines_per_iMCU_row;
      /* It is complex to properly move to the middle of a context block, so
       * read the remaining lines instead of skipping them.
       */
      read_and_discard_scanlines(cinfo, lines_to_read);
    } else {
      cinfo->output_scanline += lines_to_skip;
      cinfo->output_iMCU_row += lines_to_skip / lines_per_iMCU_row;
      increment_simple_rowgroup_ctr(cinfo, lines_to_read);
    }
    upsample->rows_to_go = cinfo->output_height - cinfo->output_scanline;
    return num_lines;
  }

  /* Skip the iMCU rows that we can safely skip. */
  for (i = 0; i < lines_to_skip; i += lines_per_iMCU_row) {
    for (y = 0; y < coef->MCU_rows_per_iMCU_row; y++) {
      for (x = 0; x < cinfo->MCUs_per_row; x++) {
        /* Calling decode_mcu() with a NULL pointer causes it to discard the
         * decoded coefficients.  This is ~5% faster for large subsets, but
         * it's tough to tell a difference for smaller images.
         */
        (*cinfo->entropy->decode_mcu) (cinfo, NULL);
      }
    }
    cinfo->input_iMCU_row++;
    cinfo->output_iMCU_row++;
    if (cinfo->input_iMCU_row < cinfo->total_iMCU_rows)
      start_iMCU_row(cinfo);
    else
      (*cinfo->inputctl->finish_input_pass) (cinfo);
  }
  cinfo->output_scanline += lines_to_skip;

  if (cinfo->upsample->need_context_rows) {
    /* Context-based upsampling keeps track of iMCU rows. */
    main_ptr->iMCU_row_ctr += lines_to_skip / lines_per_iMCU_row;

    /* It is complex to properly move to the middle of a context block, so
     * read the remaining lines instead of skipping them.
     */
    read_and_discard_scanlines(cinfo, lines_to_read);
  } else {
    increment_simple_rowgroup_ctr(cinfo, lines_to_read);
  }

  /* Since skipping lines involves skipping the upsampling step, the value of
   * "rows_to_go" will become invalid unless we set it here.  NOTE: This is a
   * bit odd, since "rows_to_go" seems to be redundantly keeping track of
   * output_scanline.
   */
  upsample->rows_to_go = cinfo->output_height - cinfo->output_scanline;

  /* Always skip the requested number of lines. */
  return num_lines;
}

/*
 * Alternate entry point to read raw data.
 * Processes exactly one iMCU row per call, unless suspended.
 */

GLOBAL(JDIMENSION)
jpeg_read_raw_data (j_decompress_ptr cinfo, JSAMPIMAGE data,
                    JDIMENSION max_lines)
{
  JDIMENSION lines_per_iMCU_row;

  if (cinfo->global_state != DSTATE_RAW_OK)
    ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
  if (cinfo->output_scanline >= cinfo->output_height) {
    WARNMS(cinfo, JWRN_TOO_MUCH_DATA);
    return 0;
  }

  /* Call progress monitor hook if present */
  if (cinfo->progress != NULL) {
    cinfo->progress->pass_counter = (long) cinfo->output_scanline;
    cinfo->progress->pass_limit = (long) cinfo->output_height;
    (*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo);
  }

  /* Verify that at least one iMCU row can be returned. */
  lines_per_iMCU_row = cinfo->max_v_samp_factor * cinfo->_min_DCT_scaled_size;
  if (max_lines < lines_per_iMCU_row)
    ERREXIT(cinfo, JERR_BUFFER_SIZE);

  /* Decompress directly into user's buffer. */
  if (! (*cinfo->coef->decompress_data) (cinfo, data))
    return 0;                   /* suspension forced, can do nothing more */

  /* OK, we processed one iMCU row. */
  cinfo->output_scanline += lines_per_iMCU_row;
  return lines_per_iMCU_row;
}


/* Additional entry points for buffered-image mode. */

#ifdef D_MULTISCAN_FILES_SUPPORTED

/*
 * Initialize for an output pass in buffered-image mode.
 */

GLOBAL(boolean)
jpeg_start_output (j_decompress_ptr cinfo, int scan_number)
{
  if (cinfo->global_state != DSTATE_BUFIMAGE &&
      cinfo->global_state != DSTATE_PRESCAN)
    ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
  /* Limit scan number to valid range */
  if (scan_number <= 0)
    scan_number = 1;
  if (cinfo->inputctl->eoi_reached &&
      scan_number > cinfo->input_scan_number)
    scan_number = cinfo->input_scan_number;
  cinfo->output_scan_number = scan_number;
  /* Perform any dummy output passes, and set up for the real pass */
  return output_pass_setup(cinfo);
}


/*
 * Finish up after an output pass in buffered-image mode.
 *
 * Returns FALSE if suspended.  The return value need be inspected only if
 * a suspending data source is used.
 */

GLOBAL(boolean)
jpeg_finish_output (j_decompress_ptr cinfo)
{
  if ((cinfo->global_state == DSTATE_SCANNING ||
       cinfo->global_state == DSTATE_RAW_OK) && cinfo->buffered_image) {
    /* Terminate this pass. */
    /* We do not require the whole pass to have been completed. */
    (*cinfo->master->finish_output_pass) (cinfo);
    cinfo->global_state = DSTATE_BUFPOST;
  } else if (cinfo->global_state != DSTATE_BUFPOST) {
    /* BUFPOST = repeat call after a suspension, anything else is error */
    ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
  }
  /* Read markers looking for SOS or EOI */
  while (cinfo->input_scan_number <= cinfo->output_scan_number &&
         ! cinfo->inputctl->eoi_reached) {
    if ((*cinfo->inputctl->consume_input) (cinfo) == JPEG_SUSPENDED)
      return FALSE;             /* Suspend, come back later */
  }
  cinfo->global_state = DSTATE_BUFIMAGE;
  return TRUE;
}

#endif /* D_MULTISCAN_FILES_SUPPORTED */