/*

 * jdmainct.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 main buffer controller for decompression.

 * The main buffer lies between the JPEG decompressor proper and the

 * post-processor; it holds downsampled data in the JPEG colorspace.

 *

 * Note that this code is bypassed in raw-data mode, since the application

 * supplies the equivalent of the main buffer in that case.

 */

#define JPEG_INTERNALS

#include "jinclude.h"

#include "jpeglib.h"

/*

 * In the current system design, the main buffer need never be a full-image

 * buffer; any full-height buffers will be found inside the coefficient or

 * postprocessing controllers.  Nonetheless, the main controller is not

 * trivial.  Its responsibility is to provide context rows for upsampling/

 * rescaling, and doing this in an efficient fashion is a bit tricky.

 *

 * Postprocessor input data is counted in "row groups".  A row group

 * is defined to be (v_samp_factor * DCT_scaled_size / min_DCT_scaled_size)

 * sample rows of each component.  (We require DCT_scaled_size values to be

 * chosen such that these numbers are integers.  In practice DCT_scaled_size

 * values will likely be powers of two, so we actually have the stronger

 * condition that DCT_scaled_size / min_DCT_scaled_size is an integer.)

 * Upsampling will typically produce max_v_samp_factor pixel rows from each

 * row group (times any additional scale factor that the upsampler is

 * applying).

 *

 * The coefficient controller will deliver data to us one iMCU row at a time;

 * each iMCU row contains v_samp_factor * DCT_scaled_size sample rows, or

 * exactly min_DCT_scaled_size row groups.  (This amount of data corresponds

 * to one row of MCUs when the image is fully interleaved.)  Note that the

 * number of sample rows varies across components, but the number of row

 * groups does not.  Some garbage sample rows may be included in the last iMCU

 * row at the bottom of the image.

 *

 * Depending on the vertical scaling algorithm used, the upsampler may need

 * access to the sample row(s) above and below its current input row group.

 * The upsampler is required to set need_context_rows TRUE at global selection

 * time if so.  When need_context_rows is FALSE, this controller can simply

 * obtain one iMCU row at a time from the coefficient controller and dole it

 * out as row groups to the postprocessor.

 *

 * When need_context_rows is TRUE, this controller guarantees that the buffer

 * passed to postprocessing contains at least one row group's worth of samples

 * above and below the row group(s) being processed.  Note that the context

 * rows "above" the first passed row group appear at negative row offsets in

 * the passed buffer.  At the top and bottom of the image, the required

 * context rows are manufactured by duplicating the first or last real sample

 * row; this avoids having special cases in the upsampling inner loops.

 *

 * The amount of context is fixed at one row group just because that's a

 * convenient number for this controller to work with.  The existing

 * upsamplers really only need one sample row of context.  An upsampler

 * supporting arbitrary output rescaling might wish for more than one row

 * group of context when shrinking the image; tough, we don't handle that.

 * (This is justified by the assumption that downsizing will be handled mostly

 * by adjusting the DCT_scaled_size values, so that the actual scale factor at

 * the upsample step needn't be much less than one.)

 *

 * To provide the desired context, we have to retain the last two row groups

 * of one iMCU row while reading in the next iMCU row.  (The last row group

 * can't be processed until we have another row group for its below-context,

 * and so we have to save the next-to-last group too for its above-context.)

 * We could do this most simply by copying data around in our buffer, but

 * that'd be very slow.  We can avoid copying any data by creating a rather

 * strange pointer structure.  Here's how it works.  We allocate a workspace

 * consisting of M+2 row groups (where M = min_DCT_scaled_size is the number

 * of row groups per iMCU row).  We create two sets of redundant pointers to

 * the workspace.  Labeling the physical row groups 0 to M+1, the synthesized

 * pointer lists look like this:

 *                   M+1                          M-1

 * master pointer --> 0         master pointer --> 0

 *                    1                            1

 *                   ...                          ...

 *                   M-3                          M-3

 *                   M-2                           M

 *                   M-1                          M+1

 *                    M                           M-2

 *                   M+1                          M-1

 *                    0                            0

 * We read alternate iMCU rows using each master pointer; thus the last two

 * row groups of the previous iMCU row remain un-overwritten in the workspace.

 * The pointer lists are set up so that the required context rows appear to

 * be adjacent to the proper places when we pass the pointer lists to the

 * upsampler.

 *

 * The above pictures describe the normal state of the pointer lists.

 * At top and bottom of the image, we diddle the pointer lists to duplicate

 * the first or last sample row as necessary (this is cheaper than copying

 * sample rows around).

 *

 * This scheme breaks down if M < 2, ie, min_DCT_scaled_size is 1.  In that

 * situation each iMCU row provides only one row group so the buffering logic

 * must be different (eg, we must read two iMCU rows before we can emit the

 * first row group).  For now, we simply do not support providing context

 * rows when min_DCT_scaled_size is 1.  That combination seems unlikely to

 * be worth providing --- if someone wants a 1/8th-size preview, they probably

 * want it quick and dirty, so a context-free upsampler is sufficient.

 */

/* Private buffer controller object */

typedef struct {

  struct jpeg_d_main_controller pub; /* public fields */

  /* Pointer to allocated workspace (M or M+2 row groups). */

  JSAMPARRAY buffer[MAX_COMPONENTS];

  boolean buffer_full;		/* Have we gotten an iMCU row from decoder? */

  JDIMENSION rowgroup_ctr;	/* counts row groups output to postprocessor */

  /* Remaining fields are only used in the context case. */

  /* These are the master pointers to the funny-order pointer lists. */

  JSAMPIMAGE xbuffer[2];	/* pointers to weird pointer lists */

  int whichptr;			/* indicates which pointer set is now in use */

  int context_state;		/* process_data state machine status */

  JDIMENSION rowgroups_avail;	/* row groups available to postprocessor */

  JDIMENSION iMCU_row_ctr;	/* counts iMCU rows to detect image top/bot */

} my_main_controller;

typedef my_main_controller * my_main_ptr;

/* context_state values: */

#define CTX_PREPARE_FOR_IMCU	0	/* need to prepare for MCU row */

#define CTX_PROCESS_IMCU	1	/* feeding iMCU to postprocessor */

#define CTX_POSTPONED_ROW	2	/* feeding postponed row group */

/* Forward declarations */

METHODDEF(void) process_data_simple_main

	JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,

	     JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));

METHODDEF(void) process_data_context_main

	JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,

	     JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));

#ifdef QUANT_2PASS_SUPPORTED

METHODDEF(void) process_data_crank_post

	JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,

	     JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));

#endif

LOCAL(void)

alloc_funny_pointers (j_decompress_ptr cinfo)

/* Allocate space for the funny pointer lists.

 * This is done only once, not once per pass.

 */

{

  my_main_ptr main = (my_main_ptr) cinfo->main;

  int ci, rgroup;

  jpeg_component_info *compptr;

  JSAMPARRAY xbuf;

  /* Get top-level space for component array pointers.

   * We alloc both arrays with one call to save a few cycles.

   */

  main->xbuffer[0] = (JSAMPIMAGE)

    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

				cinfo->num_components * 2 * SIZEOF(JSAMPARRAY));

  main->xbuffer[1] = main->xbuffer[0] + cinfo->num_components;

  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;

       ci++, compptr++) {

    /* Get space for pointer lists --- M+4 row groups in each list.

     * We alloc both pointer lists with one call to save a few cycles.

     */

    xbuf = (JSAMPARRAY)

      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

				  2 * (rgroup * (M + 4)) * SIZEOF(JSAMPROW));

    xbuf += rgroup;		/* want one row group at negative offsets */

    main->xbuffer[0][ci] = xbuf;

    xbuf += rgroup * (M + 4);

    main->xbuffer[1][ci] = xbuf;

  }

}

LOCAL(void)

make_funny_pointers (j_decompress_ptr cinfo)

/* Create the funny pointer lists discussed in the comments above.

 * The actual workspace is already allocated (in main->buffer),

 * and the space for the pointer lists is allocated too.

 * This routine just fills in the curiously ordered lists.

 * This will be repeated at the beginning of each pass.

 */

{

  my_main_ptr main = (my_main_ptr) cinfo->main;

  int ci, i, rgroup;

  jpeg_component_info *compptr;

  JSAMPARRAY buf, xbuf0, xbuf1;

  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;

       ci++, compptr++) {

    xbuf0 = main->xbuffer[0][ci];

    xbuf1 = main->xbuffer[1][ci];

    /* First copy the workspace pointers as-is */

    buf = main->buffer[ci];

    for (i = 0; i < rgroup * (M + 2); i++) {

      xbuf0[i] = xbuf1[i] = buf[i];

    }

    /* In the second list, put the last four row groups in swapped order */

    for (i = 0; i < rgroup * 2; i++) {

      xbuf1[rgroup*(M-2) + i] = buf[rgroup*M + i];

      xbuf1[rgroup*M + i] = buf[rgroup*(M-2) + i];

    }

    /* The wraparound pointers at top and bottom will be filled later

     * (see set_wraparound_pointers, below).  Initially we want the "above"

     * pointers to duplicate the first actual data line.  This only needs

     * to happen in xbuffer[0].

     */

    for (i = 0; i < rgroup; i++) {

      xbuf0[i - rgroup] = xbuf0[0];

    }

  }

}

LOCAL(void)

set_wraparound_pointers (j_decompress_ptr cinfo)

/* Set up the "wraparound" pointers at top and bottom of the pointer lists.

 * This changes the pointer list state from top-of-image to the normal state.

 */

{

  my_main_ptr main = (my_main_ptr) cinfo->main;

  int ci, i, rgroup;

  jpeg_component_info *compptr;

  JSAMPARRAY xbuf0, xbuf1;

  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;

       ci++, compptr++) {

    xbuf0 = main->xbuffer[0][ci];

    xbuf1 = main->xbuffer[1][ci];

    for (i = 0; i < rgroup; i++) {

      xbuf0[i - rgroup] = xbuf0[rgroup*(M+1) + i];

      xbuf1[i - rgroup] = xbuf1[rgroup*(M+1) + i];

      xbuf0[rgroup*(M+2) + i] = xbuf0[i];

      xbuf1[rgroup*(M+2) + i] = xbuf1[i];

    }

  }

}

LOCAL(void)

set_bottom_pointers (j_decompress_ptr cinfo)

/* Change the pointer lists to duplicate the last sample row at the bottom

 * of the image.  whichptr indicates which xbuffer holds the final iMCU row.

 * Also sets rowgroups_avail to indicate number of nondummy row groups in row.

 */

{

  my_main_ptr main = (my_main_ptr) cinfo->main;

  int ci, i, rgroup, iMCUheight, rows_left;

  jpeg_component_info *compptr;

  JSAMPARRAY xbuf;

  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;

       ci++, compptr++) {

    /* Count sample rows in one iMCU row and in one row group */

    /* Count nondummy sample rows remaining for this component */

    rows_left = (int) (compptr->downsampled_height % (JDIMENSION) iMCUheight);

    if (rows_left == 0) rows_left = iMCUheight;

    /* Count nondummy row groups.  Should get same answer for each component,

     * so we need only do it once.

     */

    if (ci == 0) {

      main->rowgroups_avail = (JDIMENSION) ((rows_left-1) / rgroup + 1);

    }

    /* Duplicate the last real sample row rgroup*2 times; this pads out the

     * last partial rowgroup and ensures at least one full rowgroup of context.

     */

    xbuf = main->xbuffer[main->whichptr][ci];

    for (i = 0; i < rgroup * 2; i++) {

      xbuf[rows_left + i] = xbuf[rows_left-1];

    }

  }

}

/*

 * Initialize for a processing pass.

 */

METHODDEF(void)

start_pass_main (j_decompress_ptr cinfo, J_BUF_MODE pass_mode)

{

  my_main_ptr main = (my_main_ptr) cinfo->main;

  switch (pass_mode) {

  case JBUF_PASS_THRU:

    if (cinfo->upsample->need_context_rows) {

      main->pub.process_data = process_data_context_main;

      make_funny_pointers(cinfo); /* Create the xbuffer[] lists */

      main->whichptr = 0;	/* Read first iMCU row into xbuffer[0] */

      main->context_state = CTX_PREPARE_FOR_IMCU;

      main->iMCU_row_ctr = 0;

    } else {

      /* Simple case with no context needed */

      main->pub.process_data = process_data_simple_main;

    }

    main->buffer_full = FALSE;	/* Mark buffer empty */

    main->rowgroup_ctr = 0;

    break;

#ifdef QUANT_2PASS_SUPPORTED

  case JBUF_CRANK_DEST:

    /* For last pass of 2-pass quantization, just crank the postprocessor */

    main->pub.process_data = process_data_crank_post;

    break;

#endif

  default:

    ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);

    break;

  }

}

/*

 * Process some data.

 * This handles the simple case where no context is required.

 */

METHODDEF(void)

process_data_simple_main (j_decompress_ptr cinfo,

			  JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,

			  JDIMENSION out_rows_avail)

{

  my_main_ptr main = (my_main_ptr) cinfo->main;

  JDIMENSION rowgroups_avail;

  /* Read input data if we haven't filled the main buffer yet */

  if (! main->buffer_full) {

    if (! (*cinfo->coef->decompress_data) (cinfo, main->buffer))

      return;			/* suspension forced, can do nothing more */

    main->buffer_full = TRUE;	/* OK, we have an iMCU row to work with */

  }

  /* There are always min_DCT_scaled_size row groups in an iMCU row. */

  /* Note: at the bottom of the image, we may pass extra garbage row groups

   * to the postprocessor.  The postprocessor has to check for bottom

   * of image anyway (at row resolution), so no point in us doing it too.

   */

  /* Feed the postprocessor */

  (*cinfo->post->post_process_data) (cinfo, main->buffer,

				     &main->rowgroup_ctr, rowgroups_avail,

				     output_buf, out_row_ctr, out_rows_avail);

  /* Has postprocessor consumed all the data yet? If so, mark buffer empty */

  if (main->rowgroup_ctr >= rowgroups_avail) {

    main->buffer_full = FALSE;

    main->rowgroup_ctr = 0;

  }

}

/*

 * Process some data.

 * This handles the case where context rows must be provided.

 */

METHODDEF(void)

process_data_context_main (j_decompress_ptr cinfo,

			   JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,

			   JDIMENSION out_rows_avail)

{

  my_main_ptr main = (my_main_ptr) cinfo->main;

  /* Read input data if we haven't filled the main buffer yet */

  if (! main->buffer_full) {

    if (! (*cinfo->coef->decompress_data) (cinfo,

					   main->xbuffer[main->whichptr]))

      return;			/* suspension forced, can do nothing more */

    main->buffer_full = TRUE;	/* OK, we have an iMCU row to work with */

    main->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 (main->context_state) {

  case CTX_POSTPONED_ROW:

    /* Call postprocessor using previously set pointers for postponed row */

    (*cinfo->post->post_process_data) (cinfo, main->xbuffer[main->whichptr],

			&main->rowgroup_ctr, main->rowgroups_avail,

			output_buf, out_row_ctr, out_rows_avail);

    if (main->rowgroup_ctr < main->rowgroups_avail)

      return;			/* Need to suspend */

    main->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 */

    main->rowgroup_ctr = 0;

    /* Check for bottom of image: if so, tweak pointers to "duplicate"

     * the last sample row, and adjust rowgroups_avail to ignore padding rows.

     */

    if (main->iMCU_row_ctr == cinfo->total_iMCU_rows)

      set_bottom_pointers(cinfo);

    main->context_state = CTX_PROCESS_IMCU;

    /*FALLTHROUGH*/

  case CTX_PROCESS_IMCU:

    /* Call postprocessor using previously set pointers */

    (*cinfo->post->post_process_data) (cinfo, main->xbuffer[main->whichptr],

			&main->rowgroup_ctr, main->rowgroups_avail,

			output_buf, out_row_ctr, out_rows_avail);

    if (main->rowgroup_ctr < main->rowgroups_avail)

      return;			/* Need to suspend */

    /* After the first iMCU, change wraparound pointers to normal state */

    if (main->iMCU_row_ctr == 1)

      set_wraparound_pointers(cinfo);

    /* Prepare to load new iMCU row using other xbuffer list */

    main->whichptr ^= 1;	/* 0=>1 or 1=>0 */

    main->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 */

    main->context_state = CTX_POSTPONED_ROW;

  }

}

/*

 * Process some data.

 * Final pass of two-pass quantization: just call the postprocessor.

 * Source data will be the postprocessor controller's internal buffer.

 */

#ifdef QUANT_2PASS_SUPPORTED

METHODDEF(void)

process_data_crank_post (j_decompress_ptr cinfo,

			 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,

			 JDIMENSION out_rows_avail)

{

  (*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE) NULL,

				     (JDIMENSION *) NULL, (JDIMENSION) 0,

				     output_buf, out_row_ctr, out_rows_avail);

}

#endif /* QUANT_2PASS_SUPPORTED */

/*

 * Initialize main buffer controller.

 */

GLOBAL(void)

jinit_d_main_controller (j_decompress_ptr cinfo, boolean need_full_buffer)

{

  my_main_ptr main;

  int ci, rgroup, ngroups;

  jpeg_component_info *compptr;

  main = (my_main_ptr)

    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

				SIZEOF(my_main_controller));

  cinfo->main = (struct jpeg_d_main_controller *) main;

  main->pub.start_pass = start_pass_main;

  if (need_full_buffer)		/* shouldn't happen */

    ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);

  /* Allocate the workspace.

   * ngroups is the number of row groups we need.

   */

  if (cinfo->upsample->need_context_rows) {

      ERREXIT(cinfo, JERR_NOTIMPL);

    alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */

  } else {

  }

  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;

       ci++, compptr++) {

    main->buffer[ci] = (*cinfo->mem->alloc_sarray)

			((j_common_ptr) cinfo, JPOOL_IMAGE,

			 (JDIMENSION) (rgroup * ngroups));

  }

}