jcprepct.cpp

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/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          http://www.mrpt.org/                          |
   |                                                                        |
   | Copyright (c) 2005-2017, Individual contributors, see AUTHORS file     |
   | See: http://www.mrpt.org/Authors - All rights reserved.                |
   | Released under BSD License. See details in http://www.mrpt.org/License |
   +------------------------------------------------------------------------+ */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "mrpt_jpeglib.h"

/* 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)
{
        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;

        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 * DCTSIZE,
                                        (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;

        /* 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 = (*cinfo->mem->alloc_sarray)(
                        (j_common_ptr)cinfo, JPOOL_IMAGE,
                        (JDIMENSION)(
                                ((long)compptr->width_in_blocks * DCTSIZE *
                                 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
                 */
                MEMCOPY(
                        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;

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