//  * jdmainct.c
//  *
//  * Copyright (C) 1994-1995, 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;
  int M = cinfo->min_DCT_scaled_size;
  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++) {
    rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
      cinfo->min_DCT_scaled_size; // height of a row group of component 
//  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;
  int M = cinfo->min_DCT_scaled_size;
  jpeg_component_info *compptr;
  JSAMPARRAY buf, xbuf0, xbuf1;

  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
       ci++, compptr++) {
    rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
      cinfo->min_DCT_scaled_size; // height of a row group of component 
    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;
  int M = cinfo->min_DCT_scaled_size;
  jpeg_component_info *compptr;
  JSAMPARRAY xbuf0, xbuf1;

  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
       ci++, compptr++) {
    rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
      cinfo->min_DCT_scaled_size; // height of a row group of component 
    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 
    iMCUheight = compptr->v_samp_factor * compptr->DCT_scaled_size;
    rgroup = iMCUheight / cinfo->min_DCT_scaled_size;
    // 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. 
  rowgroups_avail = (JDIMENSION) cinfo->min_DCT_scaled_size;
//  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;
    main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_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 (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->rowgroup_ctr = (JDIMENSION) (cinfo->min_DCT_scaled_size + 1);
    main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size + 2);
    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) {
    if (cinfo->min_DCT_scaled_size < 2) // unsupported, see comments above 
      ERREXIT(cinfo, JERR_NOTIMPL);
    alloc_funny_pointers(cinfo); // Alloc space for xbuffer[] lists 
    ngroups = cinfo->min_DCT_scaled_size + 2;
  } else {
    ngroups = cinfo->min_DCT_scaled_size;
  }

  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
       ci++, compptr++) {
    rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
      cinfo->min_DCT_scaled_size; // height of a row group of component 
    main->buffer[ci] = (*cinfo->mem->alloc_sarray)
			((j_common_ptr) cinfo, JPOOL_IMAGE,
			 compptr->width_in_blocks * compptr->DCT_scaled_size,
			 (JDIMENSION) (rgroup * ngroups));
  }
}