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1 /*
2 * jdmainct.c
3 *
4 * Copyright (C) 1994-1996, Thomas G. Lane.
5 * This file is part of the Independent JPEG Group's software.
6 * For conditions of distribution and use, see the accompanying README file.
7 *
8 * This file contains the main buffer controller for decompression.
9 * The main buffer lies between the JPEG decompressor proper and the
10 * post-processor; it holds downsampled data in the JPEG colorspace.
11 *
12 * Note that this code is bypassed in raw-data mode, since the application
13 * supplies the equivalent of the main buffer in that case.
14 */
15
16 /* suppress the warnings about using main for the variable names */
17 #define main jpegMain
18
19 #define JPEG_INTERNALS
20 #include "jinclude.h"
21 #include "jpeglib.h"
22
23 /*
24 * In the current system design, the main buffer need never be a full-image
25 * buffer; any full-height buffers will be found inside the coefficient or
26 * postprocessing controllers. Nonetheless, the main controller is not
27 * trivial. Its responsibility is to provide context rows for upsampling/
28 * rescaling, and doing this in an efficient fashion is a bit tricky.
29 *
30 * Postprocessor input data is counted in "row groups". A row group
31 * is defined to be (v_samp_factor * DCT_scaled_size / min_DCT_scaled_size)
32 * sample rows of each component. (We require DCT_scaled_size values to be
33 * chosen such that these numbers are integers. In practice DCT_scaled_size
34 * values will likely be powers of two, so we actually have the stronger
35 * condition that DCT_scaled_size / min_DCT_scaled_size is an integer.)
36 * Upsampling will typically produce max_v_samp_factor pixel rows from each
37 * row group (times any additional scale factor that the upsampler is
38 * applying).
39 *
40 * The coefficient controller will deliver data to us one iMCU row at a time;
41 * each iMCU row contains v_samp_factor * DCT_scaled_size sample rows, or
42 * exactly min_DCT_scaled_size row groups. (This amount of data corresponds
43 * to one row of MCUs when the image is fully interleaved.) Note that the
44 * number of sample rows varies across components, but the number of row
45 * groups does not. Some garbage sample rows may be included in the last iMCU
46 * row at the bottom of the image.
47 *
48 * Depending on the vertical scaling algorithm used, the upsampler may need
49 * access to the sample row(s) above and below its current input row group.
50 * The upsampler is required to set need_context_rows TRUE at global selection
51 * time if so. When need_context_rows is FALSE, this controller can simply
52 * obtain one iMCU row at a time from the coefficient controller and dole it
53 * out as row groups to the postprocessor.
54 *
55 * When need_context_rows is TRUE, this controller guarantees that the buffer
56 * passed to postprocessing contains at least one row group's worth of samples
57 * above and below the row group(s) being processed. Note that the context
58 * rows "above" the first passed row group appear at negative row offsets in
59 * the passed buffer. At the top and bottom of the image, the required
60 * context rows are manufactured by duplicating the first or last real sample
61 * row; this avoids having special cases in the upsampling inner loops.
62 *
63 * The amount of context is fixed at one row group just because that's a
64 * convenient number for this controller to work with. The existing
65 * upsamplers really only need one sample row of context. An upsampler
66 * supporting arbitrary output rescaling might wish for more than one row
67 * group of context when shrinking the image; tough, we don't handle that.
68 * (This is justified by the assumption that downsizing will be handled mostly
69 * by adjusting the DCT_scaled_size values, so that the actual scale factor at
70 * the upsample step needn't be much less than one.)
71 *
72 * To provide the desired context, we have to retain the last two row groups
73 * of one iMCU row while reading in the next iMCU row. (The last row group
74 * can't be processed until we have another row group for its below-context,
75 * and so we have to save the next-to-last group too for its above-context.)
76 * We could do this most simply by copying data around in our buffer, but
77 * that'd be very slow. We can avoid copying any data by creating a rather
78 * strange pointer structure. Here's how it works. We allocate a workspace
79 * consisting of M+2 row groups (where M = min_DCT_scaled_size is the number
80 * of row groups per iMCU row). We create two sets of redundant pointers to
81 * the workspace. Labeling the physical row groups 0 to M+1, the synthesized
82 * pointer lists look like this:
83 * M+1 M-1
84 * master pointer --> 0 master pointer --> 0
85 * 1 1
86 * ... ...
87 * M-3 M-3
88 * M-2 M
89 * M-1 M+1
90 * M M-2
91 * M+1 M-1
92 * 0 0
93 * We read alternate iMCU rows using each master pointer; thus the last two
94 * row groups of the previous iMCU row remain un-overwritten in the workspace.
95 * The pointer lists are set up so that the required context rows appear to
96 * be adjacent to the proper places when we pass the pointer lists to the
97 * upsampler.
98 *
99 * The above pictures describe the normal state of the pointer lists.
100 * At top and bottom of the image, we diddle the pointer lists to duplicate
101 * the first or last sample row as necessary (this is cheaper than copying
102 * sample rows around).
103 *
104 * This scheme breaks down if M < 2, ie, min_DCT_scaled_size is 1. In that
105 * situation each iMCU row provides only one row group so the buffering logic
106 * must be different (eg, we must read two iMCU rows before we can emit the
107 * first row group). For now, we simply do not support providing context
108 * rows when min_DCT_scaled_size is 1. That combination seems unlikely to
109 * be worth providing --- if someone wants a 1/8th-size preview, they probably
110 * want it quick and dirty, so a context-free upsampler is sufficient.
111 */
112
113
114 /* Private buffer controller object */
115
116 typedef struct {
117 struct jpeg_d_main_controller pub; /* public fields */
118
119 /* Pointer to allocated workspace (M or M+2 row groups). */
120 JSAMPARRAY buffer[MAX_COMPONENTS];
121
122 boolean buffer_full; /* Have we gotten an iMCU row from decoder? */
123 JDIMENSION rowgroup_ctr; /* counts row groups output to postprocessor */
124
125 /* Remaining fields are only used in the context case. */
126
127 /* These are the master pointers to the funny-order pointer lists. */
128 JSAMPIMAGE xbuffer[2]; /* pointers to weird pointer lists */
129
130 int whichptr; /* indicates which pointer set is now in use */
131 int context_state; /* process_data state machine status */
132 JDIMENSION rowgroups_avail; /* row groups available to postprocessor */
133 JDIMENSION iMCU_row_ctr; /* counts iMCU rows to detect image top/bot */
134 } my_main_controller;
135
136 typedef my_main_controller * my_main_ptr;
137
138 /* context_state values: */
139 #define CTX_PREPARE_FOR_IMCU 0 /* need to prepare for MCU row */
140 #define CTX_PROCESS_IMCU 1 /* feeding iMCU to postprocessor */
141 #define CTX_POSTPONED_ROW 2 /* feeding postponed row group */
142
143
144 #if defined(__VISAGECPP__)
145 /* Visual Age fixups for multiple declarations */
146 # define start_pass_main start_pass_main2 /* already in jcmaint.c */
147 # define process_data_simple_main process_data_simple_main2 /* already in jcmaint.c */
148 #endif
149
150 /* Forward declarations */
151 METHODDEF(void) process_data_simple_main
152 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
153 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
154 METHODDEF(void) process_data_context_main
155 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
156 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
157 #ifdef QUANT_2PASS_SUPPORTED
158 METHODDEF(void) process_data_crank_post
159 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
160 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
161 #endif
162
163
164 LOCAL(void)
165 alloc_funny_pointers (j_decompress_ptr cinfo)
166 /* Allocate space for the funny pointer lists.
167 * This is done only once, not once per pass.
168 */
169 {
170 my_main_ptr main = (my_main_ptr) cinfo->main;
171 int ci, rgroup;
172 int M = cinfo->min_DCT_scaled_size;
173 jpeg_component_info *compptr;
174 JSAMPARRAY xbuf;
175
176 /* Get top-level space for component array pointers.
177 * We alloc both arrays with one call to save a few cycles.
178 */
179 main->xbuffer[0] = (JSAMPIMAGE)
180 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
181 cinfo->num_components * 2 * SIZEOF(JSAMPARRAY));
182 main->xbuffer[1] = main->xbuffer[0] + cinfo->num_components;
183
184 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
185 ci++, compptr++) {
186 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
187 cinfo->min_DCT_scaled_size; /* height of a row group of component */
188 /* Get space for pointer lists --- M+4 row groups in each list.
189 * We alloc both pointer lists with one call to save a few cycles.
190 */
191 xbuf = (JSAMPARRAY)
192 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
193 2 * (rgroup * (M + 4)) * SIZEOF(JSAMPROW));
194 xbuf += rgroup; /* want one row group at negative offsets */
195 main->xbuffer[0][ci] = xbuf;
196 xbuf += rgroup * (M + 4);
197 main->xbuffer[1][ci] = xbuf;
198 }
199 }
200
201
202 LOCAL(void)
203 make_funny_pointers (j_decompress_ptr cinfo)
204 /* Create the funny pointer lists discussed in the comments above.
205 * The actual workspace is already allocated (in main->buffer),
206 * and the space for the pointer lists is allocated too.
207 * This routine just fills in the curiously ordered lists.
208 * This will be repeated at the beginning of each pass.
209 */
210 {
211 my_main_ptr main = (my_main_ptr) cinfo->main;
212 int ci, i, rgroup;
213 int M = cinfo->min_DCT_scaled_size;
214 jpeg_component_info *compptr;
215 JSAMPARRAY buf, xbuf0, xbuf1;
216
217 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
218 ci++, compptr++) {
219 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
220 cinfo->min_DCT_scaled_size; /* height of a row group of component */
221 xbuf0 = main->xbuffer[0][ci];
222 xbuf1 = main->xbuffer[1][ci];
223 /* First copy the workspace pointers as-is */
224 buf = main->buffer[ci];
225 for (i = 0; i < rgroup * (M + 2); i++) {
226 xbuf0[i] = xbuf1[i] = buf[i];
227 }
228 /* In the second list, put the last four row groups in swapped order */
229 for (i = 0; i < rgroup * 2; i++) {
230 xbuf1[rgroup*(M-2) + i] = buf[rgroup*M + i];
231 xbuf1[rgroup*M + i] = buf[rgroup*(M-2) + i];
232 }
233 /* The wraparound pointers at top and bottom will be filled later
234 * (see set_wraparound_pointers, below). Initially we want the "above"
235 * pointers to duplicate the first actual data line. This only needs
236 * to happen in xbuffer[0].
237 */
238 for (i = 0; i < rgroup; i++) {
239 xbuf0[i - rgroup] = xbuf0[0];
240 }
241 }
242 }
243
244
245 LOCAL(void)
246 set_wraparound_pointers (j_decompress_ptr cinfo)
247 /* Set up the "wraparound" pointers at top and bottom of the pointer lists.
248 * This changes the pointer list state from top-of-image to the normal state.
249 */
250 {
251 my_main_ptr main = (my_main_ptr) cinfo->main;
252 int ci, i, rgroup;
253 int M = cinfo->min_DCT_scaled_size;
254 jpeg_component_info *compptr;
255 JSAMPARRAY xbuf0, xbuf1;
256
257 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
258 ci++, compptr++) {
259 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
260 cinfo->min_DCT_scaled_size; /* height of a row group of component */
261 xbuf0 = main->xbuffer[0][ci];
262 xbuf1 = main->xbuffer[1][ci];
263 for (i = 0; i < rgroup; i++) {
264 xbuf0[i - rgroup] = xbuf0[rgroup*(M+1) + i];
265 xbuf1[i - rgroup] = xbuf1[rgroup*(M+1) + i];
266 xbuf0[rgroup*(M+2) + i] = xbuf0[i];
267 xbuf1[rgroup*(M+2) + i] = xbuf1[i];
268 }
269 }
270 }
271
272
273 LOCAL(void)
274 set_bottom_pointers (j_decompress_ptr cinfo)
275 /* Change the pointer lists to duplicate the last sample row at the bottom
276 * of the image. whichptr indicates which xbuffer holds the final iMCU row.
277 * Also sets rowgroups_avail to indicate number of nondummy row groups in row.
278 */
279 {
280 my_main_ptr main = (my_main_ptr) cinfo->main;
281 int ci, i, rgroup, iMCUheight, rows_left;
282 jpeg_component_info *compptr;
283 JSAMPARRAY xbuf;
284
285 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
286 ci++, compptr++) {
287 /* Count sample rows in one iMCU row and in one row group */
288 iMCUheight = compptr->v_samp_factor * compptr->DCT_scaled_size;
289 rgroup = iMCUheight / cinfo->min_DCT_scaled_size;
290 /* Count nondummy sample rows remaining for this component */
291 rows_left = (int) (compptr->downsampled_height % (JDIMENSION) iMCUheight);
292 if (rows_left == 0) rows_left = iMCUheight;
293 /* Count nondummy row groups. Should get same answer for each component,
294 * so we need only do it once.
295 */
296 if (ci == 0) {
297 main->rowgroups_avail = (JDIMENSION) ((rows_left-1) / rgroup + 1);
298 }
299 /* Duplicate the last real sample row rgroup*2 times; this pads out the
300 * last partial rowgroup and ensures at least one full rowgroup of context.
301 */
302 xbuf = main->xbuffer[main->whichptr][ci];
303 for (i = 0; i < rgroup * 2; i++) {
304 xbuf[rows_left + i] = xbuf[rows_left-1];
305 }
306 }
307 }
308
309
310 /*
311 * Initialize for a processing pass.
312 */
313
314 METHODDEF(void)
315 start_pass_main (j_decompress_ptr cinfo, J_BUF_MODE pass_mode)
316 {
317 my_main_ptr main = (my_main_ptr) cinfo->main;
318
319 switch (pass_mode) {
320 case JBUF_PASS_THRU:
321 if (cinfo->upsample->need_context_rows) {
322 main->pub.process_data = process_data_context_main;
323 make_funny_pointers(cinfo); /* Create the xbuffer[] lists */
324 main->whichptr = 0; /* Read first iMCU row into xbuffer[0] */
325 main->context_state = CTX_PREPARE_FOR_IMCU;
326 main->iMCU_row_ctr = 0;
327 } else {
328 /* Simple case with no context needed */
329 main->pub.process_data = process_data_simple_main;
330 }
331 main->buffer_full = FALSE; /* Mark buffer empty */
332 main->rowgroup_ctr = 0;
333 break;
334 #ifdef QUANT_2PASS_SUPPORTED
335 case JBUF_CRANK_DEST:
336 /* For last pass of 2-pass quantization, just crank the postprocessor */
337 main->pub.process_data = process_data_crank_post;
338 break;
339 #endif
340 default:
341 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
342 break;
343 }
344 }
345
346
347 /*
348 * Process some data.
349 * This handles the simple case where no context is required.
350 */
351
352 METHODDEF(void)
353 process_data_simple_main (j_decompress_ptr cinfo,
354 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
355 JDIMENSION out_rows_avail)
356 {
357 my_main_ptr main = (my_main_ptr) cinfo->main;
358 JDIMENSION rowgroups_avail;
359
360 /* Read input data if we haven't filled the main buffer yet */
361 if (! main->buffer_full) {
362 if (! (*cinfo->coef->decompress_data) (cinfo, main->buffer))
363 return; /* suspension forced, can do nothing more */
364 main->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
365 }
366
367 /* There are always min_DCT_scaled_size row groups in an iMCU row. */
368 rowgroups_avail = (JDIMENSION) cinfo->min_DCT_scaled_size;
369 /* Note: at the bottom of the image, we may pass extra garbage row groups
370 * to the postprocessor. The postprocessor has to check for bottom
371 * of image anyway (at row resolution), so no point in us doing it too.
372 */
373
374 /* Feed the postprocessor */
375 (*cinfo->post->post_process_data) (cinfo, main->buffer,
376 &main->rowgroup_ctr, rowgroups_avail,
377 output_buf, out_row_ctr, out_rows_avail);
378
379 /* Has postprocessor consumed all the data yet? If so, mark buffer empty */
380 if (main->rowgroup_ctr >= rowgroups_avail) {
381 main->buffer_full = FALSE;
382 main->rowgroup_ctr = 0;
383 }
384 }
385
386
387 /*
388 * Process some data.
389 * This handles the case where context rows must be provided.
390 */
391
392 METHODDEF(void)
393 process_data_context_main (j_decompress_ptr cinfo,
394 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
395 JDIMENSION out_rows_avail)
396 {
397 my_main_ptr main = (my_main_ptr) cinfo->main;
398
399 /* Read input data if we haven't filled the main buffer yet */
400 if (! main->buffer_full) {
401 if (! (*cinfo->coef->decompress_data) (cinfo,
402 main->xbuffer[main->whichptr]))
403 return; /* suspension forced, can do nothing more */
404 main->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
405 main->iMCU_row_ctr++; /* count rows received */
406 }
407
408 /* Postprocessor typically will not swallow all the input data it is handed
409 * in one call (due to filling the output buffer first). Must be prepared
410 * to exit and restart. This switch lets us keep track of how far we got.
411 * Note that each case falls through to the next on successful completion.
412 */
413 switch (main->context_state) {
414 case CTX_POSTPONED_ROW:
415 /* Call postprocessor using previously set pointers for postponed row */
416 (*cinfo->post->post_process_data) (cinfo, main->xbuffer[main->whichptr],
417 &main->rowgroup_ctr, main->rowgroups_avail,
418 output_buf, out_row_ctr, out_rows_avail);
419 if (main->rowgroup_ctr < main->rowgroups_avail)
420 return; /* Need to suspend */
421 main->context_state = CTX_PREPARE_FOR_IMCU;
422 if (*out_row_ctr >= out_rows_avail)
423 return; /* Postprocessor exactly filled output buf */
424 /*FALLTHROUGH*/
425 case CTX_PREPARE_FOR_IMCU:
426 /* Prepare to process first M-1 row groups of this iMCU row */
427 main->rowgroup_ctr = 0;
428 main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size - 1);
429 /* Check for bottom of image: if so, tweak pointers to "duplicate"
430 * the last sample row, and adjust rowgroups_avail to ignore padding rows.
431 */
432 if (main->iMCU_row_ctr == cinfo->total_iMCU_rows)
433 set_bottom_pointers(cinfo);
434 main->context_state = CTX_PROCESS_IMCU;
435 /*FALLTHROUGH*/
436 case CTX_PROCESS_IMCU:
437 /* Call postprocessor using previously set pointers */
438 (*cinfo->post->post_process_data) (cinfo, main->xbuffer[main->whichptr],
439 &main->rowgroup_ctr, main->rowgroups_avail,
440 output_buf, out_row_ctr, out_rows_avail);
441 if (main->rowgroup_ctr < main->rowgroups_avail)
442 return; /* Need to suspend */
443 /* After the first iMCU, change wraparound pointers to normal state */
444 if (main->iMCU_row_ctr == 1)
445 set_wraparound_pointers(cinfo);
446 /* Prepare to load new iMCU row using other xbuffer list */
447 main->whichptr ^= 1; /* 0=>1 or 1=>0 */
448 main->buffer_full = FALSE;
449 /* Still need to process last row group of this iMCU row, */
450 /* which is saved at index M+1 of the other xbuffer */
451 main->rowgroup_ctr = (JDIMENSION) (cinfo->min_DCT_scaled_size + 1);
452 main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size + 2);
453 main->context_state = CTX_POSTPONED_ROW;
454 }
455 }
456
457
458 /*
459 * Process some data.
460 * Final pass of two-pass quantization: just call the postprocessor.
461 * Source data will be the postprocessor controller's internal buffer.
462 */
463
464 #ifdef QUANT_2PASS_SUPPORTED
465
466 METHODDEF(void)
467 process_data_crank_post (j_decompress_ptr cinfo,
468 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
469 JDIMENSION out_rows_avail)
470 {
471 (*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE) NULL,
472 (JDIMENSION *) NULL, (JDIMENSION) 0,
473 output_buf, out_row_ctr, out_rows_avail);
474 }
475
476 #endif /* QUANT_2PASS_SUPPORTED */
477
478
479 /*
480 * Initialize main buffer controller.
481 */
482
483 GLOBAL(void)
484 jinit_d_main_controller (j_decompress_ptr cinfo, boolean need_full_buffer)
485 {
486 my_main_ptr main;
487 int ci, rgroup, ngroups;
488 jpeg_component_info *compptr;
489
490 main = (my_main_ptr)
491 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
492 SIZEOF(my_main_controller));
493 cinfo->main = (struct jpeg_d_main_controller *) main;
494 main->pub.start_pass = start_pass_main;
495
496 if (need_full_buffer) /* shouldn't happen */
497 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
498
499 /* Allocate the workspace.
500 * ngroups is the number of row groups we need.
501 */
502 if (cinfo->upsample->need_context_rows) {
503 if (cinfo->min_DCT_scaled_size < 2) /* unsupported, see comments above */
504 ERREXIT(cinfo, JERR_NOTIMPL);
505 alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */
506 ngroups = cinfo->min_DCT_scaled_size + 2;
507 } else {
508 ngroups = cinfo->min_DCT_scaled_size;
509 }
510
511 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
512 ci++, compptr++) {
513 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
514 cinfo->min_DCT_scaled_size; /* height of a row group of component */
515 main->buffer[ci] = (*cinfo->mem->alloc_sarray)
516 ((j_common_ptr) cinfo, JPOOL_IMAGE,
517 compptr->width_in_blocks * compptr->DCT_scaled_size,
518 (JDIMENSION) (rgroup * ngroups));
519 }
520 }
521
522 #if defined(__VISAGECPP__)
523 # ifdef start_pass_main2
524 # undef start_pass_main2
525 # endif
526 # ifdef process_data_simple_main2
527 # undef process_data_simple_main2
528 # endif
529 #endif