    /*
     * jcprepct.c
     *
     * Copyright (C) 1994-1996, Thomas G. Lane.
     * 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 compression preprocessing controller.
     * This controller manages the color conversion, downsampling,
     * and edge expansion steps.
     *
     * Most of the complexity here is associated with buffering input rows
     * as required by the downsampler.  See the comments at the head of
     * jcsample.c for the downsampler's needs.
     */

    #define JPEG_INTERNALS
    #include "jinclude.h"
    #include "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, int 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);
        }
      }
    }