7 * Copyright (C) 1994-1995, Thomas G. Lane.
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9 * This file is part of the Independent JPEG Group's software.
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11 * For conditions of distribution and use, see the accompanying README file.
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15 * This file contains the main buffer controller for decompression.
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17 * The main buffer lies between the JPEG decompressor proper and the
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19 * post-processor; it holds downsampled data in the JPEG colorspace.
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23 * Note that this code is bypassed in raw-data mode, since the application
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25 * supplies the equivalent of the main buffer in that case.
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31 #define JPEG_INTERNALS
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33 #include "jinclude.h"
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35 #include "radiant_jpeglib.h"
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43 * In the current system design, the main buffer need never be a full-image
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45 * buffer; any full-height buffers will be found inside the coefficient or
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47 * postprocessing controllers. Nonetheless, the main controller is not
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49 * trivial. Its responsibility is to provide context rows for upsampling/
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51 * rescaling, and doing this in an efficient fashion is a bit tricky.
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55 * Postprocessor input data is counted in "row groups". A row group
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57 * is defined to be (v_samp_factor * DCT_scaled_size / min_DCT_scaled_size)
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59 * sample rows of each component. (We require DCT_scaled_size values to be
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61 * chosen such that these numbers are integers. In practice DCT_scaled_size
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63 * values will likely be powers of two, so we actually have the stronger
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65 * condition that DCT_scaled_size / min_DCT_scaled_size is an integer.)
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67 * Upsampling will typically produce max_v_samp_factor pixel rows from each
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69 * row group (times any additional scale factor that the upsampler is
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75 * The coefficient controller will deliver data to us one iMCU row at a time;
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77 * each iMCU row contains v_samp_factor * DCT_scaled_size sample rows, or
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79 * exactly min_DCT_scaled_size row groups. (This amount of data corresponds
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81 * to one row of MCUs when the image is fully interleaved.) Note that the
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83 * number of sample rows varies across components, but the number of row
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85 * groups does not. Some garbage sample rows may be included in the last iMCU
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87 * row at the bottom of the image.
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91 * Depending on the vertical scaling algorithm used, the upsampler may need
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93 * access to the sample row(s) above and below its current input row group.
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95 * The upsampler is required to set need_context_rows TRUE at global selection
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97 * time if so. When need_context_rows is FALSE, this controller can simply
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99 * obtain one iMCU row at a time from the coefficient controller and dole it
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101 * out as row groups to the postprocessor.
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105 * When need_context_rows is TRUE, this controller guarantees that the buffer
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107 * passed to postprocessing contains at least one row group's worth of samples
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109 * above and below the row group(s) being processed. Note that the context
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111 * rows "above" the first passed row group appear at negative row offsets in
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113 * the passed buffer. At the top and bottom of the image, the required
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115 * context rows are manufactured by duplicating the first or last real sample
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117 * row; this avoids having special cases in the upsampling inner loops.
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121 * The amount of context is fixed at one row group just because that's a
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123 * convenient number for this controller to work with. The existing
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125 * upsamplers really only need one sample row of context. An upsampler
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127 * supporting arbitrary output rescaling might wish for more than one row
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129 * group of context when shrinking the image; tough, we don't handle that.
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131 * (This is justified by the assumption that downsizing will be handled mostly
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133 * by adjusting the DCT_scaled_size values, so that the actual scale factor at
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135 * the upsample step needn't be much less than one.)
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139 * To provide the desired context, we have to retain the last two row groups
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141 * of one iMCU row while reading in the next iMCU row. (The last row group
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143 * can't be processed until we have another row group for its below-context,
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145 * and so we have to save the next-to-last group too for its above-context.)
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147 * We could do this most simply by copying data around in our buffer, but
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149 * that'd be very slow. We can avoid copying any data by creating a rather
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151 * strange pointer structure. Here's how it works. We allocate a workspace
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153 * consisting of M+2 row groups (where M = min_DCT_scaled_size is the number
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155 * of row groups per iMCU row). We create two sets of redundant pointers to
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157 * the workspace. Labeling the physical row groups 0 to M+1, the synthesized
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159 * pointer lists look like this:
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163 * master pointer --> 0 master pointer --> 0
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181 * We read alternate iMCU rows using each master pointer; thus the last two
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183 * row groups of the previous iMCU row remain un-overwritten in the workspace.
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185 * The pointer lists are set up so that the required context rows appear to
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187 * be adjacent to the proper places when we pass the pointer lists to the
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193 * The above pictures describe the normal state of the pointer lists.
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195 * At top and bottom of the image, we diddle the pointer lists to duplicate
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197 * the first or last sample row as necessary (this is cheaper than copying
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199 * sample rows around).
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203 * This scheme breaks down if M < 2, ie, min_DCT_scaled_size is 1. In that
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205 * situation each iMCU row provides only one row group so the buffering logic
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207 * must be different (eg, we must read two iMCU rows before we can emit the
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209 * first row group). For now, we simply do not support providing context
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211 * rows when min_DCT_scaled_size is 1. That combination seems unlikely to
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213 * be worth providing --- if someone wants a 1/8th-size preview, they probably
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215 * want it quick and dirty, so a context-free upsampler is sufficient.
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223 /* Private buffer controller object */
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229 struct jpeg_d_main_controller pub; /* public fields */
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233 /* Pointer to allocated workspace (M or M+2 row groups). */
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235 JSAMPARRAY buffer[MAX_COMPONENTS];
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239 boolean buffer_full; /* Have we gotten an iMCU row from decoder? */
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241 JDIMENSION rowgroup_ctr; /* counts row groups output to postprocessor */
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245 /* Remaining fields are only used in the context case. */
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249 /* These are the master pointers to the funny-order pointer lists. */
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251 JSAMPIMAGE xbuffer[2]; /* pointers to weird pointer lists */
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255 int whichptr; /* indicates which pointer set is now in use */
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257 int context_state; /* process_data state machine status */
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259 JDIMENSION rowgroups_avail; /* row groups available to postprocessor */
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261 JDIMENSION iMCU_row_ctr; /* counts iMCU rows to detect image top/bot */
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263 } my_main_controller;
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267 typedef my_main_controller * my_main_ptr;
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271 /* context_state values: */
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273 #define CTX_PREPARE_FOR_IMCU 0 /* need to prepare for MCU row */
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275 #define CTX_PROCESS_IMCU 1 /* feeding iMCU to postprocessor */
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277 #define CTX_POSTPONED_ROW 2 /* feeding postponed row group */
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283 /* Forward declarations */
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285 METHODDEF void process_data_simple_main
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287 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
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289 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
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291 METHODDEF void process_data_context_main
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293 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
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295 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
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297 #ifdef QUANT_2PASS_SUPPORTED
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299 METHODDEF void process_data_crank_post
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301 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
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303 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
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313 alloc_funny_pointers (j_decompress_ptr cinfo)
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315 /* Allocate space for the funny pointer lists.
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317 * This is done only once, not once per pass.
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323 my_main_ptr main = (my_main_ptr) cinfo->main;
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327 int M = cinfo->min_DCT_scaled_size;
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329 jpeg_component_info *compptr;
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335 /* Get top-level space for component array pointers.
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337 * We alloc both arrays with one call to save a few cycles.
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341 main->xbuffer[0] = (JSAMPIMAGE)
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343 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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345 cinfo->num_components * 2 * SIZEOF(JSAMPARRAY));
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347 main->xbuffer[1] = main->xbuffer[0] + cinfo->num_components;
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351 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
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355 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
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357 cinfo->min_DCT_scaled_size; /* height of a row group of component */
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359 /* Get space for pointer lists --- M+4 row groups in each list.
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361 * We alloc both pointer lists with one call to save a few cycles.
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365 xbuf = (JSAMPARRAY)
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367 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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369 2 * (rgroup * (M + 4)) * SIZEOF(JSAMPROW));
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371 xbuf += rgroup; /* want one row group at negative offsets */
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373 main->xbuffer[0][ci] = xbuf;
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375 xbuf += rgroup * (M + 4);
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377 main->xbuffer[1][ci] = xbuf;
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389 make_funny_pointers (j_decompress_ptr cinfo)
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391 /* Create the funny pointer lists discussed in the comments above.
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393 * The actual workspace is already allocated (in main->buffer),
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395 * and the space for the pointer lists is allocated too.
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397 * This routine just fills in the curiously ordered lists.
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399 * This will be repeated at the beginning of each pass.
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405 my_main_ptr main = (my_main_ptr) cinfo->main;
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409 int M = cinfo->min_DCT_scaled_size;
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411 jpeg_component_info *compptr;
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413 JSAMPARRAY buf, xbuf0, xbuf1;
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417 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
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421 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
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423 cinfo->min_DCT_scaled_size; /* height of a row group of component */
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425 xbuf0 = main->xbuffer[0][ci];
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427 xbuf1 = main->xbuffer[1][ci];
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429 /* First copy the workspace pointers as-is */
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431 buf = main->buffer[ci];
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433 for (i = 0; i < rgroup * (M + 2); i++) {
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435 xbuf0[i] = xbuf1[i] = buf[i];
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439 /* In the second list, put the last four row groups in swapped order */
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441 for (i = 0; i < rgroup * 2; i++) {
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443 xbuf1[rgroup*(M-2) + i] = buf[rgroup*M + i];
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445 xbuf1[rgroup*M + i] = buf[rgroup*(M-2) + i];
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449 /* The wraparound pointers at top and bottom will be filled later
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451 * (see set_wraparound_pointers, below). Initially we want the "above"
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453 * pointers to duplicate the first actual data line. This only needs
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455 * to happen in xbuffer[0].
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459 for (i = 0; i < rgroup; i++) {
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461 xbuf0[i - rgroup] = xbuf0[0];
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475 set_wraparound_pointers (j_decompress_ptr cinfo)
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477 /* Set up the "wraparound" pointers at top and bottom of the pointer lists.
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479 * This changes the pointer list state from top-of-image to the normal state.
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485 my_main_ptr main = (my_main_ptr) cinfo->main;
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489 int M = cinfo->min_DCT_scaled_size;
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491 jpeg_component_info *compptr;
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493 JSAMPARRAY xbuf0, xbuf1;
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497 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
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501 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
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503 cinfo->min_DCT_scaled_size; /* height of a row group of component */
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505 xbuf0 = main->xbuffer[0][ci];
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507 xbuf1 = main->xbuffer[1][ci];
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509 for (i = 0; i < rgroup; i++) {
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511 xbuf0[i - rgroup] = xbuf0[rgroup*(M+1) + i];
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513 xbuf1[i - rgroup] = xbuf1[rgroup*(M+1) + i];
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515 xbuf0[rgroup*(M+2) + i] = xbuf0[i];
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517 xbuf1[rgroup*(M+2) + i] = xbuf1[i];
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531 set_bottom_pointers (j_decompress_ptr cinfo)
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533 /* Change the pointer lists to duplicate the last sample row at the bottom
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535 * of the image. whichptr indicates which xbuffer holds the final iMCU row.
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537 * Also sets rowgroups_avail to indicate number of nondummy row groups in row.
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543 my_main_ptr main = (my_main_ptr) cinfo->main;
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545 int ci, i, rgroup, iMCUheight, rows_left;
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547 jpeg_component_info *compptr;
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553 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
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557 /* Count sample rows in one iMCU row and in one row group */
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559 iMCUheight = compptr->v_samp_factor * compptr->DCT_scaled_size;
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561 rgroup = iMCUheight / cinfo->min_DCT_scaled_size;
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563 /* Count nondummy sample rows remaining for this component */
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565 rows_left = (int) (compptr->downsampled_height % (JDIMENSION) iMCUheight);
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567 if (rows_left == 0) rows_left = iMCUheight;
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569 /* Count nondummy row groups. Should get same answer for each component,
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571 * so we need only do it once.
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577 main->rowgroups_avail = (JDIMENSION) ((rows_left-1) / rgroup + 1);
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581 /* Duplicate the last real sample row rgroup*2 times; this pads out the
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583 * last partial rowgroup and ensures at least one full rowgroup of context.
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587 xbuf = main->xbuffer[main->whichptr][ci];
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589 for (i = 0; i < rgroup * 2; i++) {
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591 xbuf[rows_left + i] = xbuf[rows_left-1];
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605 * Initialize for a processing pass.
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613 start_pass_main (j_decompress_ptr cinfo, J_BUF_MODE pass_mode)
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617 my_main_ptr main = (my_main_ptr) cinfo->main;
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621 switch (pass_mode) {
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623 case JBUF_PASS_THRU:
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625 if (cinfo->upsample->need_context_rows) {
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627 main->pub.process_data = process_data_context_main;
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629 make_funny_pointers(cinfo); /* Create the xbuffer[] lists */
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631 main->whichptr = 0; /* Read first iMCU row into xbuffer[0] */
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633 main->context_state = CTX_PREPARE_FOR_IMCU;
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635 main->iMCU_row_ctr = 0;
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639 /* Simple case with no context needed */
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641 main->pub.process_data = process_data_simple_main;
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645 main->buffer_full = FALSE; /* Mark buffer empty */
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647 main->rowgroup_ctr = 0;
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651 #ifdef QUANT_2PASS_SUPPORTED
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653 case JBUF_CRANK_DEST:
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655 /* For last pass of 2-pass quantization, just crank the postprocessor */
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657 main->pub.process_data = process_data_crank_post;
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665 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
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679 * Process some data.
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681 * This handles the simple case where no context is required.
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689 process_data_simple_main (j_decompress_ptr cinfo,
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691 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
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693 JDIMENSION out_rows_avail)
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697 my_main_ptr main = (my_main_ptr) cinfo->main;
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699 JDIMENSION rowgroups_avail;
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703 /* Read input data if we haven't filled the main buffer yet */
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705 if (! main->buffer_full) {
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707 if (! (*cinfo->coef->decompress_data) (cinfo, main->buffer))
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709 return; /* suspension forced, can do nothing more */
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711 main->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
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717 /* There are always min_DCT_scaled_size row groups in an iMCU row. */
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719 rowgroups_avail = (JDIMENSION) cinfo->min_DCT_scaled_size;
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721 /* Note: at the bottom of the image, we may pass extra garbage row groups
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723 * to the postprocessor. The postprocessor has to check for bottom
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725 * of image anyway (at row resolution), so no point in us doing it too.
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731 /* Feed the postprocessor */
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733 (*cinfo->post->post_process_data) (cinfo, main->buffer,
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735 &main->rowgroup_ctr, rowgroups_avail,
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737 output_buf, out_row_ctr, out_rows_avail);
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741 /* Has postprocessor consumed all the data yet? If so, mark buffer empty */
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743 if (main->rowgroup_ctr >= rowgroups_avail) {
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745 main->buffer_full = FALSE;
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747 main->rowgroup_ctr = 0;
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759 * Process some data.
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761 * This handles the case where context rows must be provided.
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769 process_data_context_main (j_decompress_ptr cinfo,
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771 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
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773 JDIMENSION out_rows_avail)
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777 my_main_ptr main = (my_main_ptr) cinfo->main;
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781 /* Read input data if we haven't filled the main buffer yet */
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783 if (! main->buffer_full) {
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785 if (! (*cinfo->coef->decompress_data) (cinfo,
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787 main->xbuffer[main->whichptr]))
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789 return; /* suspension forced, can do nothing more */
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791 main->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
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793 main->iMCU_row_ctr++; /* count rows received */
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799 /* Postprocessor typically will not swallow all the input data it is handed
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801 * in one call (due to filling the output buffer first). Must be prepared
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803 * to exit and restart. This switch lets us keep track of how far we got.
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805 * Note that each case falls through to the next on successful completion.
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809 switch (main->context_state) {
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811 case CTX_POSTPONED_ROW:
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813 /* Call postprocessor using previously set pointers for postponed row */
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815 (*cinfo->post->post_process_data) (cinfo, main->xbuffer[main->whichptr],
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817 &main->rowgroup_ctr, main->rowgroups_avail,
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819 output_buf, out_row_ctr, out_rows_avail);
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821 if (main->rowgroup_ctr < main->rowgroups_avail)
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823 return; /* Need to suspend */
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825 main->context_state = CTX_PREPARE_FOR_IMCU;
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827 if (*out_row_ctr >= out_rows_avail)
\r
829 return; /* Postprocessor exactly filled output buf */
\r
833 case CTX_PREPARE_FOR_IMCU:
\r
835 /* Prepare to process first M-1 row groups of this iMCU row */
\r
837 main->rowgroup_ctr = 0;
\r
839 main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size - 1);
\r
841 /* Check for bottom of image: if so, tweak pointers to "duplicate"
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843 * the last sample row, and adjust rowgroups_avail to ignore padding rows.
\r
847 if (main->iMCU_row_ctr == cinfo->total_iMCU_rows)
\r
849 set_bottom_pointers(cinfo);
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851 main->context_state = CTX_PROCESS_IMCU;
\r
855 case CTX_PROCESS_IMCU:
\r
857 /* Call postprocessor using previously set pointers */
\r
859 (*cinfo->post->post_process_data) (cinfo, main->xbuffer[main->whichptr],
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861 &main->rowgroup_ctr, main->rowgroups_avail,
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863 output_buf, out_row_ctr, out_rows_avail);
\r
865 if (main->rowgroup_ctr < main->rowgroups_avail)
\r
867 return; /* Need to suspend */
\r
869 /* After the first iMCU, change wraparound pointers to normal state */
\r
871 if (main->iMCU_row_ctr == 1)
\r
873 set_wraparound_pointers(cinfo);
\r
875 /* Prepare to load new iMCU row using other xbuffer list */
\r
877 main->whichptr ^= 1; /* 0=>1 or 1=>0 */
\r
879 main->buffer_full = FALSE;
\r
881 /* Still need to process last row group of this iMCU row, */
\r
883 /* which is saved at index M+1 of the other xbuffer */
\r
885 main->rowgroup_ctr = (JDIMENSION) (cinfo->min_DCT_scaled_size + 1);
\r
887 main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size + 2);
\r
889 main->context_state = CTX_POSTPONED_ROW;
\r
901 * Process some data.
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903 * Final pass of two-pass quantization: just call the postprocessor.
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905 * Source data will be the postprocessor controller's internal buffer.
\r
911 #ifdef QUANT_2PASS_SUPPORTED
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917 process_data_crank_post (j_decompress_ptr cinfo,
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919 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
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921 JDIMENSION out_rows_avail)
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925 (*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE) NULL,
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927 (JDIMENSION *) NULL, (JDIMENSION) 0,
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929 output_buf, out_row_ctr, out_rows_avail);
\r
935 #endif /* QUANT_2PASS_SUPPORTED */
\r
943 * Initialize main buffer controller.
\r
951 jinit_d_main_controller (j_decompress_ptr cinfo, boolean need_full_buffer)
\r
957 int ci, rgroup, ngroups;
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959 jpeg_component_info *compptr;
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963 main = (my_main_ptr)
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965 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
\r
967 SIZEOF(my_main_controller));
\r
969 cinfo->main = (struct jpeg_d_main_controller *) main;
\r
971 main->pub.start_pass = start_pass_main;
\r
975 if (need_full_buffer) /* shouldn't happen */
\r
977 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
\r
981 /* Allocate the workspace.
\r
983 * ngroups is the number of row groups we need.
\r
987 if (cinfo->upsample->need_context_rows) {
\r
989 if (cinfo->min_DCT_scaled_size < 2) /* unsupported, see comments above */
\r
991 ERREXIT(cinfo, JERR_NOTIMPL);
\r
993 alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */
\r
995 ngroups = cinfo->min_DCT_scaled_size + 2;
\r
999 ngroups = cinfo->min_DCT_scaled_size;
\r
1005 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
\r
1007 ci++, compptr++) {
\r
1009 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
\r
1011 cinfo->min_DCT_scaled_size; /* height of a row group of component */
\r
1013 main->buffer[ci] = (*cinfo->mem->alloc_sarray)
\r
1015 ((j_common_ptr) cinfo, JPOOL_IMAGE,
\r
1017 compptr->width_in_blocks * compptr->DCT_scaled_size,
\r
1019 (JDIMENSION) (rgroup * ngroups));
\r