process_data_context_main (j_decompress_ptr cinfo,
JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
JDIMENSION out_rows_avail)
{
my_main_ptr mainptr = (my_main_ptr) cinfo->main;
/* Read input data if we haven't filled the main buffer yet */
if (! mainptr->buffer_full) {
if (! (*cinfo->coef->decompress_data) (cinfo,
mainptr->xbuffer[mainptr->whichptr]))
return; /* suspension forced, can do nothing more */
mainptr->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
mainptr->iMCU_row_ctr++; /* count rows received */
}
/* Postprocessor typically will not swallow all the input data it is handed
* in one call (due to filling the output buffer first). Must be prepared
* to exit and restart. This switch lets us keep track of how far we got.
* Note that each case falls through to the next on successful completion.
*/
switch (mainptr->context_state) {
case CTX_POSTPONED_ROW:
/* Call postprocessor using previously set pointers for postponed row */
(*cinfo->post->post_process_data) (cinfo, mainptr->xbuffer[mainptr->whichptr],
&mainptr->rowgroup_ctr, mainptr->rowgroups_avail,
output_buf, out_row_ctr, out_rows_avail);
if (mainptr->rowgroup_ctr < mainptr->rowgroups_avail)
return; /* Need to suspend */
mainptr->context_state = CTX_PREPARE_FOR_IMCU;
if (*out_row_ctr >= out_rows_avail)
return; /* Postprocessor exactly filled output buf */
/*FALLTHROUGH*/
case CTX_PREPARE_FOR_IMCU:
/* Prepare to process first M-1 row groups of this iMCU row */
mainptr->rowgroup_ctr = 0;
mainptr->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_v_scaled_size - 1);
/* Check for bottom of image: if so, tweak pointers to "duplicate"
* the last sample row, and adjust rowgroups_avail to ignore padding rows.
*/
if (mainptr->iMCU_row_ctr == cinfo->total_iMCU_rows)
set_bottom_pointers(cinfo);
mainptr->context_state = CTX_PROCESS_IMCU;
/*FALLTHROUGH*/
case CTX_PROCESS_IMCU:
/* Call postprocessor using previously set pointers */
(*cinfo->post->post_process_data) (cinfo, mainptr->xbuffer[mainptr->whichptr],
&mainptr->rowgroup_ctr, mainptr->rowgroups_avail,
output_buf, out_row_ctr, out_rows_avail);
if (mainptr->rowgroup_ctr < mainptr->rowgroups_avail)
return; /* Need to suspend */
/* After the first iMCU, change wraparound pointers to normal state */
if (mainptr->iMCU_row_ctr == 1)
set_wraparound_pointers(cinfo);
/* Prepare to load new iMCU row using other xbuffer list */
mainptr->whichptr ^= 1; /* 0=>1 or 1=>0 */
mainptr->buffer_full = FALSE;
/* Still need to process last row group of this iMCU row, */
/* which is saved at index M+1 of the other xbuffer */
mainptr->rowgroup_ctr = (JDIMENSION) (cinfo->min_DCT_v_scaled_size + 1);
mainptr->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_v_scaled_size + 2);
mainptr->context_state = CTX_POSTPONED_ROW;
}
}
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;
}
