jdmainct.c 19 KB

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