Line data Source code
1 : /*
2 : * jdmainct.c
3 : *
4 : * This file was part of the Independent JPEG Group's software:
5 : * Copyright (C) 1994-1996, Thomas G. Lane.
6 : * libjpeg-turbo Modifications:
7 : * Copyright (C) 2010, 2016, D. R. Commander.
8 : * For conditions of distribution and use, see the accompanying README.ijg
9 : * file.
10 : *
11 : * This file contains the main buffer controller for decompression.
12 : * The main buffer lies between the JPEG decompressor proper and the
13 : * post-processor; it holds downsampled data in the JPEG colorspace.
14 : *
15 : * Note that this code is bypassed in raw-data mode, since the application
16 : * supplies the equivalent of the main buffer in that case.
17 : */
18 :
19 : #include "jinclude.h"
20 : #include "jdmainct.h"
21 :
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 : /* Forward declarations */
115 : METHODDEF(void) process_data_simple_main
116 : (j_decompress_ptr cinfo, JSAMPARRAY output_buf,
117 : JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail);
118 : METHODDEF(void) process_data_context_main
119 : (j_decompress_ptr cinfo, JSAMPARRAY output_buf,
120 : JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail);
121 : #ifdef QUANT_2PASS_SUPPORTED
122 : METHODDEF(void) process_data_crank_post
123 : (j_decompress_ptr cinfo, JSAMPARRAY output_buf,
124 : JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail);
125 : #endif
126 :
127 :
128 : LOCAL(void)
129 0 : alloc_funny_pointers (j_decompress_ptr cinfo)
130 : /* Allocate space for the funny pointer lists.
131 : * This is done only once, not once per pass.
132 : */
133 : {
134 0 : my_main_ptr main_ptr = (my_main_ptr) cinfo->main;
135 : int ci, rgroup;
136 0 : int M = cinfo->_min_DCT_scaled_size;
137 : jpeg_component_info *compptr;
138 : JSAMPARRAY xbuf;
139 :
140 : /* Get top-level space for component array pointers.
141 : * We alloc both arrays with one call to save a few cycles.
142 : */
143 0 : main_ptr->xbuffer[0] = (JSAMPIMAGE)
144 0 : (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
145 0 : cinfo->num_components * 2 * sizeof(JSAMPARRAY));
146 0 : main_ptr->xbuffer[1] = main_ptr->xbuffer[0] + cinfo->num_components;
147 :
148 0 : for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
149 0 : ci++, compptr++) {
150 0 : rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) /
151 0 : cinfo->_min_DCT_scaled_size; /* height of a row group of component */
152 : /* Get space for pointer lists --- M+4 row groups in each list.
153 : * We alloc both pointer lists with one call to save a few cycles.
154 : */
155 0 : xbuf = (JSAMPARRAY)
156 0 : (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
157 0 : 2 * (rgroup * (M + 4)) * sizeof(JSAMPROW));
158 0 : xbuf += rgroup; /* want one row group at negative offsets */
159 0 : main_ptr->xbuffer[0][ci] = xbuf;
160 0 : xbuf += rgroup * (M + 4);
161 0 : main_ptr->xbuffer[1][ci] = xbuf;
162 : }
163 0 : }
164 :
165 :
166 : LOCAL(void)
167 0 : make_funny_pointers (j_decompress_ptr cinfo)
168 : /* Create the funny pointer lists discussed in the comments above.
169 : * The actual workspace is already allocated (in main_ptr->buffer),
170 : * and the space for the pointer lists is allocated too.
171 : * This routine just fills in the curiously ordered lists.
172 : * This will be repeated at the beginning of each pass.
173 : */
174 : {
175 0 : my_main_ptr main_ptr = (my_main_ptr) cinfo->main;
176 : int ci, i, rgroup;
177 0 : int M = cinfo->_min_DCT_scaled_size;
178 : jpeg_component_info *compptr;
179 : JSAMPARRAY buf, xbuf0, xbuf1;
180 :
181 0 : for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
182 0 : ci++, compptr++) {
183 0 : rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) /
184 0 : cinfo->_min_DCT_scaled_size; /* height of a row group of component */
185 0 : xbuf0 = main_ptr->xbuffer[0][ci];
186 0 : xbuf1 = main_ptr->xbuffer[1][ci];
187 : /* First copy the workspace pointers as-is */
188 0 : buf = main_ptr->buffer[ci];
189 0 : for (i = 0; i < rgroup * (M + 2); i++) {
190 0 : xbuf0[i] = xbuf1[i] = buf[i];
191 : }
192 : /* In the second list, put the last four row groups in swapped order */
193 0 : for (i = 0; i < rgroup * 2; i++) {
194 0 : xbuf1[rgroup*(M-2) + i] = buf[rgroup*M + i];
195 0 : xbuf1[rgroup*M + i] = buf[rgroup*(M-2) + i];
196 : }
197 : /* The wraparound pointers at top and bottom will be filled later
198 : * (see set_wraparound_pointers, below). Initially we want the "above"
199 : * pointers to duplicate the first actual data line. This only needs
200 : * to happen in xbuffer[0].
201 : */
202 0 : for (i = 0; i < rgroup; i++) {
203 0 : xbuf0[i - rgroup] = xbuf0[0];
204 : }
205 : }
206 0 : }
207 :
208 :
209 : LOCAL(void)
210 0 : set_bottom_pointers (j_decompress_ptr cinfo)
211 : /* Change the pointer lists to duplicate the last sample row at the bottom
212 : * of the image. whichptr indicates which xbuffer holds the final iMCU row.
213 : * Also sets rowgroups_avail to indicate number of nondummy row groups in row.
214 : */
215 : {
216 0 : my_main_ptr main_ptr = (my_main_ptr) cinfo->main;
217 : int ci, i, rgroup, iMCUheight, rows_left;
218 : jpeg_component_info *compptr;
219 : JSAMPARRAY xbuf;
220 :
221 0 : for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
222 0 : ci++, compptr++) {
223 : /* Count sample rows in one iMCU row and in one row group */
224 0 : iMCUheight = compptr->v_samp_factor * compptr->_DCT_scaled_size;
225 0 : rgroup = iMCUheight / cinfo->_min_DCT_scaled_size;
226 : /* Count nondummy sample rows remaining for this component */
227 0 : rows_left = (int) (compptr->downsampled_height % (JDIMENSION) iMCUheight);
228 0 : if (rows_left == 0) rows_left = iMCUheight;
229 : /* Count nondummy row groups. Should get same answer for each component,
230 : * so we need only do it once.
231 : */
232 0 : if (ci == 0) {
233 0 : main_ptr->rowgroups_avail = (JDIMENSION) ((rows_left-1) / rgroup + 1);
234 : }
235 : /* Duplicate the last real sample row rgroup*2 times; this pads out the
236 : * last partial rowgroup and ensures at least one full rowgroup of context.
237 : */
238 0 : xbuf = main_ptr->xbuffer[main_ptr->whichptr][ci];
239 0 : for (i = 0; i < rgroup * 2; i++) {
240 0 : xbuf[rows_left + i] = xbuf[rows_left-1];
241 : }
242 : }
243 0 : }
244 :
245 :
246 : /*
247 : * Initialize for a processing pass.
248 : */
249 :
250 : METHODDEF(void)
251 0 : start_pass_main (j_decompress_ptr cinfo, J_BUF_MODE pass_mode)
252 : {
253 0 : my_main_ptr main_ptr = (my_main_ptr) cinfo->main;
254 :
255 0 : switch (pass_mode) {
256 : case JBUF_PASS_THRU:
257 0 : if (cinfo->upsample->need_context_rows) {
258 0 : main_ptr->pub.process_data = process_data_context_main;
259 0 : make_funny_pointers(cinfo); /* Create the xbuffer[] lists */
260 0 : main_ptr->whichptr = 0; /* Read first iMCU row into xbuffer[0] */
261 0 : main_ptr->context_state = CTX_PREPARE_FOR_IMCU;
262 0 : main_ptr->iMCU_row_ctr = 0;
263 : } else {
264 : /* Simple case with no context needed */
265 0 : main_ptr->pub.process_data = process_data_simple_main;
266 : }
267 0 : main_ptr->buffer_full = FALSE; /* Mark buffer empty */
268 0 : main_ptr->rowgroup_ctr = 0;
269 0 : break;
270 : #ifdef QUANT_2PASS_SUPPORTED
271 : case JBUF_CRANK_DEST:
272 : /* For last pass of 2-pass quantization, just crank the postprocessor */
273 0 : main_ptr->pub.process_data = process_data_crank_post;
274 0 : break;
275 : #endif
276 : default:
277 0 : ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
278 0 : break;
279 : }
280 0 : }
281 :
282 :
283 : /*
284 : * Process some data.
285 : * This handles the simple case where no context is required.
286 : */
287 :
288 : METHODDEF(void)
289 0 : process_data_simple_main (j_decompress_ptr cinfo,
290 : JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
291 : JDIMENSION out_rows_avail)
292 : {
293 0 : my_main_ptr main_ptr = (my_main_ptr) cinfo->main;
294 : JDIMENSION rowgroups_avail;
295 :
296 : /* Read input data if we haven't filled the main buffer yet */
297 0 : if (! main_ptr->buffer_full) {
298 0 : if (! (*cinfo->coef->decompress_data) (cinfo, main_ptr->buffer))
299 0 : return; /* suspension forced, can do nothing more */
300 0 : main_ptr->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
301 : }
302 :
303 : /* There are always min_DCT_scaled_size row groups in an iMCU row. */
304 0 : rowgroups_avail = (JDIMENSION) cinfo->_min_DCT_scaled_size;
305 : /* Note: at the bottom of the image, we may pass extra garbage row groups
306 : * to the postprocessor. The postprocessor has to check for bottom
307 : * of image anyway (at row resolution), so no point in us doing it too.
308 : */
309 :
310 : /* Feed the postprocessor */
311 0 : (*cinfo->post->post_process_data) (cinfo, main_ptr->buffer,
312 : &main_ptr->rowgroup_ctr, rowgroups_avail,
313 : output_buf, out_row_ctr, out_rows_avail);
314 :
315 : /* Has postprocessor consumed all the data yet? If so, mark buffer empty */
316 0 : if (main_ptr->rowgroup_ctr >= rowgroups_avail) {
317 0 : main_ptr->buffer_full = FALSE;
318 0 : main_ptr->rowgroup_ctr = 0;
319 : }
320 : }
321 :
322 :
323 : /*
324 : * Process some data.
325 : * This handles the case where context rows must be provided.
326 : */
327 :
328 : METHODDEF(void)
329 0 : process_data_context_main (j_decompress_ptr cinfo,
330 : JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
331 : JDIMENSION out_rows_avail)
332 : {
333 0 : my_main_ptr main_ptr = (my_main_ptr) cinfo->main;
334 :
335 : /* Read input data if we haven't filled the main buffer yet */
336 0 : if (! main_ptr->buffer_full) {
337 0 : if (! (*cinfo->coef->decompress_data) (cinfo,
338 0 : main_ptr->xbuffer[main_ptr->whichptr]))
339 0 : return; /* suspension forced, can do nothing more */
340 0 : main_ptr->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
341 0 : main_ptr->iMCU_row_ctr++; /* count rows received */
342 : }
343 :
344 : /* Postprocessor typically will not swallow all the input data it is handed
345 : * in one call (due to filling the output buffer first). Must be prepared
346 : * to exit and restart. This switch lets us keep track of how far we got.
347 : * Note that each case falls through to the next on successful completion.
348 : */
349 0 : switch (main_ptr->context_state) {
350 : case CTX_POSTPONED_ROW:
351 : /* Call postprocessor using previously set pointers for postponed row */
352 0 : (*cinfo->post->post_process_data) (cinfo, main_ptr->xbuffer[main_ptr->whichptr],
353 : &main_ptr->rowgroup_ctr, main_ptr->rowgroups_avail,
354 : output_buf, out_row_ctr, out_rows_avail);
355 0 : if (main_ptr->rowgroup_ctr < main_ptr->rowgroups_avail)
356 0 : return; /* Need to suspend */
357 0 : main_ptr->context_state = CTX_PREPARE_FOR_IMCU;
358 0 : if (*out_row_ctr >= out_rows_avail)
359 0 : return; /* Postprocessor exactly filled output buf */
360 : /*FALLTHROUGH*/
361 : case CTX_PREPARE_FOR_IMCU:
362 : /* Prepare to process first M-1 row groups of this iMCU row */
363 0 : main_ptr->rowgroup_ctr = 0;
364 0 : main_ptr->rowgroups_avail = (JDIMENSION) (cinfo->_min_DCT_scaled_size - 1);
365 : /* Check for bottom of image: if so, tweak pointers to "duplicate"
366 : * the last sample row, and adjust rowgroups_avail to ignore padding rows.
367 : */
368 0 : if (main_ptr->iMCU_row_ctr == cinfo->total_iMCU_rows)
369 0 : set_bottom_pointers(cinfo);
370 0 : main_ptr->context_state = CTX_PROCESS_IMCU;
371 : /*FALLTHROUGH*/
372 : case CTX_PROCESS_IMCU:
373 : /* Call postprocessor using previously set pointers */
374 0 : (*cinfo->post->post_process_data) (cinfo, main_ptr->xbuffer[main_ptr->whichptr],
375 : &main_ptr->rowgroup_ctr, main_ptr->rowgroups_avail,
376 : output_buf, out_row_ctr, out_rows_avail);
377 0 : if (main_ptr->rowgroup_ctr < main_ptr->rowgroups_avail)
378 0 : return; /* Need to suspend */
379 : /* After the first iMCU, change wraparound pointers to normal state */
380 0 : if (main_ptr->iMCU_row_ctr == 1)
381 0 : set_wraparound_pointers(cinfo);
382 : /* Prepare to load new iMCU row using other xbuffer list */
383 0 : main_ptr->whichptr ^= 1; /* 0=>1 or 1=>0 */
384 0 : main_ptr->buffer_full = FALSE;
385 : /* Still need to process last row group of this iMCU row, */
386 : /* which is saved at index M+1 of the other xbuffer */
387 0 : main_ptr->rowgroup_ctr = (JDIMENSION) (cinfo->_min_DCT_scaled_size + 1);
388 0 : main_ptr->rowgroups_avail = (JDIMENSION) (cinfo->_min_DCT_scaled_size + 2);
389 0 : main_ptr->context_state = CTX_POSTPONED_ROW;
390 : }
391 : }
392 :
393 :
394 : /*
395 : * Process some data.
396 : * Final pass of two-pass quantization: just call the postprocessor.
397 : * Source data will be the postprocessor controller's internal buffer.
398 : */
399 :
400 : #ifdef QUANT_2PASS_SUPPORTED
401 :
402 : METHODDEF(void)
403 0 : process_data_crank_post (j_decompress_ptr cinfo,
404 : JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
405 : JDIMENSION out_rows_avail)
406 : {
407 0 : (*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE) NULL,
408 : (JDIMENSION *) NULL, (JDIMENSION) 0,
409 : output_buf, out_row_ctr, out_rows_avail);
410 0 : }
411 :
412 : #endif /* QUANT_2PASS_SUPPORTED */
413 :
414 :
415 : /*
416 : * Initialize main buffer controller.
417 : */
418 :
419 : GLOBAL(void)
420 0 : jinit_d_main_controller (j_decompress_ptr cinfo, boolean need_full_buffer)
421 : {
422 : my_main_ptr main_ptr;
423 : int ci, rgroup, ngroups;
424 : jpeg_component_info *compptr;
425 :
426 0 : main_ptr = (my_main_ptr)
427 0 : (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
428 : sizeof(my_main_controller));
429 0 : cinfo->main = (struct jpeg_d_main_controller *) main_ptr;
430 0 : main_ptr->pub.start_pass = start_pass_main;
431 :
432 0 : if (need_full_buffer) /* shouldn't happen */
433 0 : ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
434 :
435 : /* Allocate the workspace.
436 : * ngroups is the number of row groups we need.
437 : */
438 0 : if (cinfo->upsample->need_context_rows) {
439 0 : if (cinfo->_min_DCT_scaled_size < 2) /* unsupported, see comments above */
440 0 : ERREXIT(cinfo, JERR_NOTIMPL);
441 0 : alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */
442 0 : ngroups = cinfo->_min_DCT_scaled_size + 2;
443 : } else {
444 0 : ngroups = cinfo->_min_DCT_scaled_size;
445 : }
446 :
447 0 : for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
448 0 : ci++, compptr++) {
449 0 : rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) /
450 0 : cinfo->_min_DCT_scaled_size; /* height of a row group of component */
451 0 : main_ptr->buffer[ci] = (*cinfo->mem->alloc_sarray)
452 : ((j_common_ptr) cinfo, JPOOL_IMAGE,
453 0 : compptr->width_in_blocks * compptr->_DCT_scaled_size,
454 0 : (JDIMENSION) (rgroup * ngroups));
455 : }
456 0 : }
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