#define JPEG_INTERNALS#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_SUPPORTEDMETHODDEF(void) process_data_crank_post	JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,	     JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));#endifLOCAL(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 mymain = (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.   */  mymain->xbuffer[0] = (JSAMPIMAGE)    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,				cinfo->num_components * 2 * SIZEOF(JSAMPARRAY));  mymain->xbuffer[1] = mymain->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 */    mymain->xbuffer[0][ci] = xbuf;    xbuf += rgroup * (M + 4);    mymain->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 mymain->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 mymain = (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 = mymain->xbuffer[0][ci];    xbuf1 = mymain->xbuffer[1][ci];    /* First copy the workspace pointers as-is */    buf = mymain->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 mymain = (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 = mymain->xbuffer[0][ci];    xbuf1 = mymain->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)