/* * jdmainct.c * * This file was part of the Independent JPEG Group's software: * Copyright (C) 1994-1996, Thomas G. Lane. * libjpeg-turbo Modifications: * Copyright (C) 2010, 2016, D. R. Commander. * For conditions of distribution and use, see the accompanying README.ijg * 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. */ #include "jinclude.h" #include "jdmainct.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. */ /* Forward declarations */ METHODDEF(void) process_data_simple_main (j_decompress_ptr cinfo, JSAMPARRAY output_buf, JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail); METHODDEF(void) process_data_context_main (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 (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_ptr = (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_ptr->xbuffer[0] = (JSAMPIMAGE) (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, cinfo->num_components * 2 * sizeof(JSAMPARRAY)); main_ptr->xbuffer[1] = main_ptr->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_ptr->xbuffer[0][ci] = xbuf; xbuf += rgroup * (M + 4); main_ptr->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_ptr->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_ptr = (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_ptr->xbuffer[0][ci]; xbuf1 = main_ptr->xbuffer[1][ci]; /* First copy the workspace pointers as-is */ buf = main_ptr->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_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_ptr = (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_ptr->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_ptr->xbuffer[main_ptr->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_ptr = (my_main_ptr) cinfo->main; switch (pass_mode) { case JBUF_PASS_THRU: if (cinfo->upsample->need_context_rows) { main_ptr->pub.process_data = process_data_context_main; make_funny_pointers(cinfo); /* Create the xbuffer[] lists */ main_ptr->whichptr = 0; /* Read first iMCU row into xbuffer[0] */ main_ptr->context_state = CTX_PREPARE_FOR_IMCU; main_ptr->iMCU_row_ctr = 0; } else { /* Simple case with no context needed */ main_ptr->pub.process_data = process_data_simple_main; } main_ptr->buffer_full = FALSE; /* Mark buffer empty */ main_ptr->rowgroup_ctr = 0; break; #ifdef QUANT_2PASS_SUPPORTED case JBUF_CRANK_DEST: /* For last pass of 2-pass quantization, just crank the postprocessor */ main_ptr->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_ptr = (my_main_ptr) cinfo->main; JDIMENSION rowgroups_avail; /* Read input data if we haven't filled the main buffer yet */ if (! main_ptr->buffer_full) { if (! (*cinfo->coef->decompress_data) (cinfo, main_ptr->buffer)) return; /* suspension forced, can do nothing more */ main_ptr->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_ptr->buffer, &main_ptr->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_ptr->rowgroup_ctr >= rowgroups_avail) { main_ptr->buffer_full = FALSE; main_ptr->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_ptr = (my_main_ptr) cinfo->main; /* Read input data if we haven't filled the main buffer yet */ if (! main_ptr->buffer_full) { if (! (*cinfo->coef->decompress_data) (cinfo, main_ptr->xbuffer[main_ptr->whichptr])) return; /* suspension forced, can do nothing more */ main_ptr->buffer_full = TRUE; /* OK, we have an iMCU row to work with */ main_ptr->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_ptr->context_state) { case CTX_POSTPONED_ROW: /* Call postprocessor using previously set pointers for postponed row */ (*cinfo->post->post_process_data) (cinfo, main_ptr->xbuffer[main_ptr->whichptr], &main_ptr->rowgroup_ctr, main_ptr->rowgroups_avail, output_buf, out_row_ctr, out_rows_avail); if (main_ptr->rowgroup_ctr < main_ptr->rowgroups_avail) return; /* Need to suspend */ main_ptr->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_ptr->rowgroup_ctr = 0; main_ptr->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_ptr->iMCU_row_ctr == cinfo->total_iMCU_rows) set_bottom_pointers(cinfo); main_ptr->context_state = CTX_PROCESS_IMCU; /*FALLTHROUGH*/ case CTX_PROCESS_IMCU: /* Call postprocessor using previously set pointers */ (*cinfo->post->post_process_data) (cinfo, main_ptr->xbuffer[main_ptr->whichptr], &main_ptr->rowgroup_ctr, main_ptr->rowgroups_avail, output_buf, out_row_ctr, out_rows_avail); if (main_ptr->rowgroup_ctr < main_ptr->rowgroups_avail) return; /* Need to suspend */ /* After the first iMCU, change wraparound pointers to normal state */ if (main_ptr->iMCU_row_ctr == 1) set_wraparound_pointers(cinfo); /* Prepare to load new iMCU row using other xbuffer list */ main_ptr->whichptr ^= 1; /* 0=>1 or 1=>0 */ main_ptr->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_ptr->rowgroup_ctr = (JDIMENSION) (cinfo->_min_DCT_scaled_size + 1); main_ptr->rowgroups_avail = (JDIMENSION) (cinfo->_min_DCT_scaled_size + 2); main_ptr->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_ptr; int ci, rgroup, ngroups; jpeg_component_info *compptr; main_ptr = (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_ptr; main_ptr->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_ptr->buffer[ci] = (*cinfo->mem->alloc_sarray) ((j_common_ptr) cinfo, JPOOL_IMAGE, compptr->width_in_blocks * compptr->_DCT_scaled_size, (JDIMENSION) (rgroup * ngroups)); } }