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* Copyright (C) 1994, Thomas G. Lane.
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* This file is part of the Independent JPEG Group's software.
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* For conditions of distribution and use, see the accompanying README file.
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* This file contains the compression preprocessing controller.
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* This controller manages the color conversion, downsampling,
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* and edge expansion steps.
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* Most of the complexity here is associated with buffering input rows
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* as required by the downsampler. See the comments at the head of
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* jcsample.c for the downsampler's needs.
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#define JPEG_INTERNALS
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/* At present, jcsample.c can request context rows only for smoothing.
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* In the future, we might also need context rows for CCIR601 sampling
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* or other more-complex downsampling procedures. The code to support
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* context rows should be compiled only if needed.
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#ifdef INPUT_SMOOTHING_SUPPORTED
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#define CONTEXT_ROWS_SUPPORTED
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* For the simple (no-context-row) case, we just need to buffer one
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* row group's worth of pixels for the downsampling step. At the bottom of
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* the image, we pad to a full row group by replicating the last pixel row.
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* The downsampler's last output row is then replicated if needed to pad
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* out to a full iMCU row.
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* When providing context rows, we must buffer three row groups' worth of
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* pixels. Three row groups are physically allocated, but the row pointer
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* arrays are made five row groups high, with the extra pointers above and
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* below "wrapping around" to point to the last and first real row groups.
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* This allows the downsampler to access the proper context rows.
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* At the top and bottom of the image, we create dummy context rows by
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* copying the first or last real pixel row. This copying could be avoided
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* by pointer hacking as is done in jdmainct.c, but it doesn't seem worth the
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* trouble on the compression side.
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/* Private buffer controller object */
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struct jpeg_c_prep_controller pub; /* public fields */
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/* Downsampling input buffer. This buffer holds color-converted data
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* until we have enough to do a downsample step.
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JSAMPARRAY color_buf[MAX_COMPONENTS];
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JDIMENSION rows_to_go; /* counts rows remaining in source image */
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int next_buf_row; /* index of next row to store in color_buf */
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#ifdef CONTEXT_ROWS_SUPPORTED /* only needed for context case */
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int this_row_group; /* starting row index of group to process */
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int next_buf_stop; /* downsample when we reach this index */
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typedef my_prep_controller * my_prep_ptr;
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* Initialize for a processing pass.
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start_pass_prep (j_compress_ptr cinfo, J_BUF_MODE pass_mode)
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my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
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if (pass_mode != JBUF_PASS_THRU)
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ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
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/* Initialize total-height counter for detecting bottom of image */
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prep->rows_to_go = cinfo->image_height;
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/* Mark the conversion buffer empty */
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prep->next_buf_row = 0;
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#ifdef CONTEXT_ROWS_SUPPORTED
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/* Preset additional state variables for context mode.
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* These aren't used in non-context mode, so we needn't test which mode.
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prep->this_row_group = 0;
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/* Set next_buf_stop to stop after two row groups have been read in. */
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prep->next_buf_stop = 2 * cinfo->max_v_samp_factor;
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* Expand an image vertically from height input_rows to height output_rows,
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* by duplicating the bottom row.
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expand_bottom_edge (JSAMPARRAY image_data, JDIMENSION num_cols,
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int input_rows, int output_rows)
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for (row = input_rows; row < output_rows; row++) {
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jcopy_sample_rows(image_data, input_rows-1, image_data, row,
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* Process some data in the simple no-context case.
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* Preprocessor output data is counted in "row groups". A row group
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* is defined to be v_samp_factor sample rows of each component.
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* Downsampling will produce this much data from each max_v_samp_factor
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pre_process_data (j_compress_ptr cinfo,
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JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
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JDIMENSION in_rows_avail,
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JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
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JDIMENSION out_row_groups_avail)
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my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
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jpeg_component_info * compptr;
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while (*in_row_ctr < in_rows_avail &&
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*out_row_group_ctr < out_row_groups_avail) {
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/* Do color conversion to fill the conversion buffer. */
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inrows = in_rows_avail - *in_row_ctr;
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numrows = cinfo->max_v_samp_factor - prep->next_buf_row;
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numrows = (int) MIN((JDIMENSION) numrows, inrows);
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(*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
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(JDIMENSION) prep->next_buf_row,
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*in_row_ctr += numrows;
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prep->next_buf_row += numrows;
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prep->rows_to_go -= numrows;
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/* If at bottom of image, pad to fill the conversion buffer. */
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if (prep->rows_to_go == 0 &&
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prep->next_buf_row < cinfo->max_v_samp_factor) {
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for (ci = 0; ci < cinfo->num_components; ci++) {
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expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
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prep->next_buf_row, cinfo->max_v_samp_factor);
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prep->next_buf_row = cinfo->max_v_samp_factor;
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/* If we've filled the conversion buffer, empty it. */
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if (prep->next_buf_row == cinfo->max_v_samp_factor) {
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(*cinfo->downsample->downsample) (cinfo,
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prep->color_buf, (JDIMENSION) 0,
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output_buf, *out_row_group_ctr);
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prep->next_buf_row = 0;
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(*out_row_group_ctr)++;
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/* If at bottom of image, pad the output to a full iMCU height.
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* Note we assume the caller is providing a one-iMCU-height output buffer!
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if (prep->rows_to_go == 0 &&
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*out_row_group_ctr < out_row_groups_avail) {
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for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
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expand_bottom_edge(output_buf[ci],
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compptr->width_in_blocks * DCTSIZE,
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(int) (*out_row_group_ctr * compptr->v_samp_factor),
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(int) (out_row_groups_avail * compptr->v_samp_factor));
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*out_row_group_ctr = out_row_groups_avail;
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break; /* can exit outer loop without test */
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#ifdef CONTEXT_ROWS_SUPPORTED
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* Process some data in the context case.
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pre_process_context (j_compress_ptr cinfo,
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JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
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JDIMENSION in_rows_avail,
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JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
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JDIMENSION out_row_groups_avail)
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my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
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int buf_height = cinfo->max_v_samp_factor * 3;
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jpeg_component_info * compptr;
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while (*out_row_group_ctr < out_row_groups_avail) {
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if (*in_row_ctr < in_rows_avail) {
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/* Do color conversion to fill the conversion buffer. */
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inrows = in_rows_avail - *in_row_ctr;
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numrows = prep->next_buf_stop - prep->next_buf_row;
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numrows = (int) MIN((JDIMENSION) numrows, inrows);
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(*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
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(JDIMENSION) prep->next_buf_row,
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/* Pad at top of image, if first time through */
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if (prep->rows_to_go == cinfo->image_height) {
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for (ci = 0; ci < cinfo->num_components; ci++) {
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for (row = 1; row <= cinfo->max_v_samp_factor; row++) {
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jcopy_sample_rows(prep->color_buf[ci], 0,
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prep->color_buf[ci], -row,
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1, cinfo->image_width);
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*in_row_ctr += numrows;
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prep->next_buf_row += numrows;
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prep->rows_to_go -= numrows;
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/* Return for more data, unless we are at the bottom of the image. */
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if (prep->rows_to_go != 0)
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/* If at bottom of image, pad to fill the conversion buffer. */
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if (prep->rows_to_go == 0 &&
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prep->next_buf_row < prep->next_buf_stop) {
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for (ci = 0; ci < cinfo->num_components; ci++) {
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expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
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prep->next_buf_row, prep->next_buf_stop);
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prep->next_buf_row = prep->next_buf_stop;
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/* If we've gotten enough data, downsample a row group. */
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if (prep->next_buf_row == prep->next_buf_stop) {
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(*cinfo->downsample->downsample) (cinfo,
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(JDIMENSION) prep->this_row_group,
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output_buf, *out_row_group_ctr);
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(*out_row_group_ctr)++;
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/* Advance pointers with wraparound as necessary. */
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prep->this_row_group += cinfo->max_v_samp_factor;
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if (prep->this_row_group >= buf_height)
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prep->this_row_group = 0;
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if (prep->next_buf_row >= buf_height)
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prep->next_buf_row = 0;
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prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor;
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/* If at bottom of image, pad the output to a full iMCU height.
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* Note we assume the caller is providing a one-iMCU-height output buffer!
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if (prep->rows_to_go == 0 &&
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*out_row_group_ctr < out_row_groups_avail) {
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for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
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expand_bottom_edge(output_buf[ci],
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compptr->width_in_blocks * DCTSIZE,
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(int) (*out_row_group_ctr * compptr->v_samp_factor),
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(int) (out_row_groups_avail * compptr->v_samp_factor));
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*out_row_group_ctr = out_row_groups_avail;
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break; /* can exit outer loop without test */
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* Create the wrapped-around downsampling input buffer needed for context mode.
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create_context_buffer (j_compress_ptr cinfo)
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my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
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int rgroup_height = cinfo->max_v_samp_factor;
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jpeg_component_info * compptr;
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JSAMPARRAY true_buffer, fake_buffer;
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/* Grab enough space for fake row pointers for all the components;
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* we need five row groups' worth of pointers for each component.
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fake_buffer = (JSAMPARRAY)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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(cinfo->num_components * 5 * rgroup_height) *
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for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
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/* Allocate the actual buffer space (3 row groups) for this component.
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* We make the buffer wide enough to allow the downsampler to edge-expand
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* horizontally within the buffer, if it so chooses.
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true_buffer = (*cinfo->mem->alloc_sarray)
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((j_common_ptr) cinfo, JPOOL_IMAGE,
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(JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
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cinfo->max_h_samp_factor) / compptr->h_samp_factor),
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(JDIMENSION) (3 * rgroup_height));
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/* Copy true buffer row pointers into the middle of the fake row array */
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MEMCOPY(fake_buffer + rgroup_height, true_buffer,
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3 * rgroup_height * SIZEOF(JSAMPROW));
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/* Fill in the above and below wraparound pointers */
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for (i = 0; i < rgroup_height; i++) {
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fake_buffer[i] = true_buffer[2 * rgroup_height + i];
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fake_buffer[4 * rgroup_height + i] = true_buffer[i];
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prep->color_buf[ci] = fake_buffer + rgroup_height;
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fake_buffer += 5 * rgroup_height; /* point to space for next component */
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#endif /* CONTEXT_ROWS_SUPPORTED */
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* Initialize preprocessing controller.
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jinit_c_prep_controller (j_compress_ptr cinfo, boolean need_full_buffer)
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jpeg_component_info * compptr;
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if (need_full_buffer) /* safety check */
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ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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SIZEOF(my_prep_controller));
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cinfo->prep = (struct jpeg_c_prep_controller *) prep;
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prep->pub.start_pass = start_pass_prep;
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/* Allocate the color conversion buffer.
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* We make the buffer wide enough to allow the downsampler to edge-expand
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* horizontally within the buffer, if it so chooses.
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if (cinfo->downsample->need_context_rows) {
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/* Set up to provide context rows */
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#ifdef CONTEXT_ROWS_SUPPORTED
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prep->pub.pre_process_data = pre_process_context;
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create_context_buffer(cinfo);
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ERREXIT(cinfo, JERR_NOT_COMPILED);
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/* No context, just make it tall enough for one row group */
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prep->pub.pre_process_data = pre_process_data;
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for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
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prep->color_buf[ci] = (*cinfo->mem->alloc_sarray)
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((j_common_ptr) cinfo, JPOOL_IMAGE,
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(JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
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cinfo->max_h_samp_factor) / compptr->h_samp_factor),
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(JDIMENSION) cinfo->max_v_samp_factor);
added
removed
code/jpeg-6/jcprepct.c
