www.pudn.com > imgport.rar > jdmainct.c, change:2008-11-05,size:21407b


/* 
 * 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. 
 */ 
 
/* suppress the warnings about using main for the variable names */ 
#define main jpegMain 
 
#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 */ 
 
 
#if defined(__VISAGECPP__) 
/* Visual Age fixups for multiple declarations */ 
#  define start_pass_main   start_pass_main2 /* already in jcmaint.c */ 
#  define process_data_simple_main process_data_simple_main2 /* already in jcmaint.c */ 
#endif 
 
/* 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)); 
  } 
} 
 
#if defined(__VISAGECPP__) 
#  ifdef start_pass_main2 
#   undef start_pass_main2 
#  endif 
#  ifdef process_data_simple_main2 
#   undef process_data_simple_main2 
#  endif 
#endif