/* * 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 ) ); } }