jdmainct.cpp 22 KB

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  1. /*
  2. * jdmainct.c
  3. *
  4. * Copyright (C) 1994-1995, 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. #define JPEG_INTERNALS
  16. #include "jinclude.h"
  17. #include "jpeglib.h"
  18. /*
  19. * In the current system design, the main buffer need never be a full-image
  20. * buffer; any full-height buffers will be found inside the coefficient or
  21. * postprocessing controllers. Nonetheless, the main controller is not
  22. * trivial. Its responsibility is to provide context rows for upsampling/
  23. * rescaling, and doing this in an efficient fashion is a bit tricky.
  24. *
  25. * Postprocessor input data is counted in "row groups". A row group
  26. * is defined to be (v_samp_factor * DCT_scaled_size / min_DCT_scaled_size)
  27. * sample rows of each component. (We require DCT_scaled_size values to be
  28. * chosen such that these numbers are integers. In practice DCT_scaled_size
  29. * values will likely be powers of two, so we actually have the stronger
  30. * condition that DCT_scaled_size / min_DCT_scaled_size is an integer.)
  31. * Upsampling will typically produce max_v_samp_factor pixel rows from each
  32. * row group (times any additional scale factor that the upsampler is
  33. * applying).
  34. *
  35. * The coefficient controller will deliver data to us one iMCU row at a time;
  36. * each iMCU row contains v_samp_factor * DCT_scaled_size sample rows, or
  37. * exactly min_DCT_scaled_size row groups. (This amount of data corresponds
  38. * to one row of MCUs when the image is fully interleaved.) Note that the
  39. * number of sample rows varies across components, but the number of row
  40. * groups does not. Some garbage sample rows may be included in the last iMCU
  41. * row at the bottom of the image.
  42. *
  43. * Depending on the vertical scaling algorithm used, the upsampler may need
  44. * access to the sample row(s) above and below its current input row group.
  45. * The upsampler is required to set need_context_rows TRUE at global selection
  46. * time if so. When need_context_rows is FALSE, this controller can simply
  47. * obtain one iMCU row at a time from the coefficient controller and dole it
  48. * out as row groups to the postprocessor.
  49. *
  50. * When need_context_rows is TRUE, this controller guarantees that the buffer
  51. * passed to postprocessing contains at least one row group's worth of samples
  52. * above and below the row group(s) being processed. Note that the context
  53. * rows "above" the first passed row group appear at negative row offsets in
  54. * the passed buffer. At the top and bottom of the image, the required
  55. * context rows are manufactured by duplicating the first or last real sample
  56. * row; this avoids having special cases in the upsampling inner loops.
  57. *
  58. * The amount of context is fixed at one row group just because that's a
  59. * convenient number for this controller to work with. The existing
  60. * upsamplers really only need one sample row of context. An upsampler
  61. * supporting arbitrary output rescaling might wish for more than one row
  62. * group of context when shrinking the image; tough, we don't handle that.
  63. * (This is justified by the assumption that downsizing will be handled mostly
  64. * by adjusting the DCT_scaled_size values, so that the actual scale factor at
  65. * the upsample step needn't be much less than one.)
  66. *
  67. * To provide the desired context, we have to retain the last two row groups
  68. * of one iMCU row while reading in the next iMCU row. (The last row group
  69. * can't be processed until we have another row group for its below-context,
  70. * and so we have to save the next-to-last group too for its above-context.)
  71. * We could do this most simply by copying data around in our buffer, but
  72. * that'd be very slow. We can avoid copying any data by creating a rather
  73. * strange pointer structure. Here's how it works. We allocate a workspace
  74. * consisting of M+2 row groups (where M = min_DCT_scaled_size is the number
  75. * of row groups per iMCU row). We create two sets of redundant pointers to
  76. * the workspace. Labeling the physical row groups 0 to M+1, the synthesized
  77. * pointer lists look like this:
  78. * M+1 M-1
  79. * master pointer --> 0 master pointer --> 0
  80. * 1 1
  81. * ... ...
  82. * M-3 M-3
  83. * M-2 M
  84. * M-1 M+1
  85. * M M-2
  86. * M+1 M-1
  87. * 0 0
  88. * We read alternate iMCU rows using each master pointer; thus the last two
  89. * row groups of the previous iMCU row remain un-overwritten in the workspace.
  90. * The pointer lists are set up so that the required context rows appear to
  91. * be adjacent to the proper places when we pass the pointer lists to the
  92. * upsampler.
  93. *
  94. * The above pictures describe the normal state of the pointer lists.
  95. * At top and bottom of the image, we diddle the pointer lists to duplicate
  96. * the first or last sample row as necessary (this is cheaper than copying
  97. * sample rows around).
  98. *
  99. * This scheme breaks down if M < 2, ie, min_DCT_scaled_size is 1. In that
  100. * situation each iMCU row provides only one row group so the buffering logic
  101. * must be different (eg, we must read two iMCU rows before we can emit the
  102. * first row group). For now, we simply do not support providing context
  103. * rows when min_DCT_scaled_size is 1. That combination seems unlikely to
  104. * be worth providing --- if someone wants a 1/8th-size preview, they probably
  105. * want it quick and dirty, so a context-free upsampler is sufficient.
  106. */
  107. /* Private buffer controller object */
  108. typedef struct {
  109. struct jpeg_d_main_controller pub;/* public fields */
  110. /* Pointer to allocated workspace (M or M+2 row groups). */
  111. JSAMPARRAY buffer[MAX_COMPONENTS];
  112. boolean buffer_full; /* Have we gotten an iMCU row from decoder? */
  113. JDIMENSION rowgroup_ctr;/* counts row groups output to postprocessor */
  114. /* Remaining fields are only used in the context case. */
  115. /* These are the master pointers to the funny-order pointer lists. */
  116. JSAMPIMAGE xbuffer[2]; /* pointers to weird pointer lists */
  117. int whichptr;/* indicates which pointer set is now in use */
  118. int context_state; /* process_data state machine status */
  119. JDIMENSION rowgroups_avail; /* row groups available to postprocessor */
  120. JDIMENSION iMCU_row_ctr;/* counts iMCU rows to detect image top/bot */
  121. } my_main_controller;
  122. typedef my_main_controller * my_main_ptr;
  123. /* context_state values: */
  124. #define CTX_PREPARE_FOR_IMCU 0 /* need to prepare for MCU row */
  125. #define CTX_PROCESS_IMCU 1 /* feeding iMCU to postprocessor */
  126. #define CTX_POSTPONED_ROW 2 /* feeding postponed row group */
  127. /* Forward declarations */
  128. METHODDEF void process_data_simple_main
  129. JPP( ( j_decompress_ptr cinfo, JSAMPARRAY output_buf,
  130. JDIMENSION * out_row_ctr, JDIMENSION out_rows_avail ) );
  131. METHODDEF void process_data_context_main
  132. JPP( ( j_decompress_ptr cinfo, JSAMPARRAY output_buf,
  133. JDIMENSION * out_row_ctr, JDIMENSION out_rows_avail ) );
  134. #ifdef QUANT_2PASS_SUPPORTED
  135. METHODDEF void process_data_crank_post
  136. JPP( ( j_decompress_ptr cinfo, JSAMPARRAY output_buf,
  137. JDIMENSION * out_row_ctr, JDIMENSION out_rows_avail ) );
  138. #endif
  139. LOCAL void
  140. alloc_funny_pointers( j_decompress_ptr cinfo ) {
  141. /* Allocate space for the funny pointer lists.
  142. * This is done only once, not once per pass.
  143. */
  144. my_main_ptr main = (my_main_ptr) cinfo->main;
  145. int ci, rgroup;
  146. int M = cinfo->min_DCT_scaled_size;
  147. jpeg_component_info * compptr;
  148. JSAMPARRAY xbuf;
  149. /* Get top-level space for component array pointers.
  150. * We alloc both arrays with one call to save a few cycles.
  151. */
  152. main->xbuffer[0] = (JSAMPIMAGE)
  153. ( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE,
  154. cinfo->num_components * 2 * SIZEOF( JSAMPARRAY ) );
  155. main->xbuffer[1] = main->xbuffer[0] + cinfo->num_components;
  156. for ( ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
  157. ci++, compptr++ ) {
  158. rgroup = ( compptr->v_samp_factor * compptr->DCT_scaled_size ) /
  159. cinfo->min_DCT_scaled_size; /* height of a row group of component */
  160. /* Get space for pointer lists --- M+4 row groups in each list.
  161. * We alloc both pointer lists with one call to save a few cycles.
  162. */
  163. xbuf = (JSAMPARRAY)
  164. ( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE,
  165. 2 * ( rgroup * ( M + 4 ) ) * SIZEOF( JSAMPROW ) );
  166. xbuf += rgroup; /* want one row group at negative offsets */
  167. main->xbuffer[0][ci] = xbuf;
  168. xbuf += rgroup * ( M + 4 );
  169. main->xbuffer[1][ci] = xbuf;
  170. }
  171. }
  172. LOCAL void
  173. make_funny_pointers( j_decompress_ptr cinfo ) {
  174. /* Create the funny pointer lists discussed in the comments above.
  175. * The actual workspace is already allocated (in main->buffer),
  176. * and the space for the pointer lists is allocated too.
  177. * This routine just fills in the curiously ordered lists.
  178. * This will be repeated at the beginning of each pass.
  179. */
  180. my_main_ptr main = (my_main_ptr) cinfo->main;
  181. int ci, i, rgroup;
  182. int M = cinfo->min_DCT_scaled_size;
  183. jpeg_component_info * compptr;
  184. JSAMPARRAY buf, xbuf0, xbuf1;
  185. for ( ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
  186. ci++, compptr++ ) {
  187. rgroup = ( compptr->v_samp_factor * compptr->DCT_scaled_size ) /
  188. cinfo->min_DCT_scaled_size; /* height of a row group of component */
  189. xbuf0 = main->xbuffer[0][ci];
  190. xbuf1 = main->xbuffer[1][ci];
  191. /* First copy the workspace pointers as-is */
  192. buf = main->buffer[ci];
  193. for ( i = 0; i < rgroup * ( M + 2 ); i++ ) {
  194. xbuf0[i] = xbuf1[i] = buf[i];
  195. }
  196. /* In the second list, put the last four row groups in swapped order */
  197. for ( i = 0; i < rgroup * 2; i++ ) {
  198. xbuf1[rgroup * ( M - 2 ) + i] = buf[rgroup * M + i];
  199. xbuf1[rgroup * M + i] = buf[rgroup * ( M - 2 ) + i];
  200. }
  201. /* The wraparound pointers at top and bottom will be filled later
  202. * (see set_wraparound_pointers, below). Initially we want the "above"
  203. * pointers to duplicate the first actual data line. This only needs
  204. * to happen in xbuffer[0].
  205. */
  206. for ( i = 0; i < rgroup; i++ ) {
  207. xbuf0[i - rgroup] = xbuf0[0];
  208. }
  209. }
  210. }
  211. LOCAL void
  212. set_wraparound_pointers( j_decompress_ptr cinfo ) {
  213. /* Set up the "wraparound" pointers at top and bottom of the pointer lists.
  214. * This changes the pointer list state from top-of-image to the normal state.
  215. */
  216. my_main_ptr main = (my_main_ptr) cinfo->main;
  217. int ci, i, rgroup;
  218. int M = cinfo->min_DCT_scaled_size;
  219. jpeg_component_info * compptr;
  220. JSAMPARRAY xbuf0, xbuf1;
  221. for ( ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
  222. ci++, compptr++ ) {
  223. rgroup = ( compptr->v_samp_factor * compptr->DCT_scaled_size ) /
  224. cinfo->min_DCT_scaled_size; /* height of a row group of component */
  225. xbuf0 = main->xbuffer[0][ci];
  226. xbuf1 = main->xbuffer[1][ci];
  227. for ( i = 0; i < rgroup; i++ ) {
  228. xbuf0[i - rgroup] = xbuf0[rgroup * ( M + 1 ) + i];
  229. xbuf1[i - rgroup] = xbuf1[rgroup * ( M + 1 ) + i];
  230. xbuf0[rgroup * ( M + 2 ) + i] = xbuf0[i];
  231. xbuf1[rgroup * ( M + 2 ) + i] = xbuf1[i];
  232. }
  233. }
  234. }
  235. LOCAL void
  236. set_bottom_pointers( j_decompress_ptr cinfo ) {
  237. /* Change the pointer lists to duplicate the last sample row at the bottom
  238. * of the image. whichptr indicates which xbuffer holds the final iMCU row.
  239. * Also sets rowgroups_avail to indicate number of nondummy row groups in row.
  240. */
  241. my_main_ptr main = (my_main_ptr) cinfo->main;
  242. int ci, i, rgroup, iMCUheight, rows_left;
  243. jpeg_component_info * compptr;
  244. JSAMPARRAY xbuf;
  245. for ( ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
  246. ci++, compptr++ ) {
  247. /* Count sample rows in one iMCU row and in one row group */
  248. iMCUheight = compptr->v_samp_factor * compptr->DCT_scaled_size;
  249. rgroup = iMCUheight / cinfo->min_DCT_scaled_size;
  250. /* Count nondummy sample rows remaining for this component */
  251. rows_left = (int) ( compptr->downsampled_height % (JDIMENSION) iMCUheight );
  252. if ( rows_left == 0 ) {
  253. rows_left = iMCUheight;
  254. }
  255. /* Count nondummy row groups. Should get same answer for each component,
  256. * so we need only do it once.
  257. */
  258. if ( ci == 0 ) {
  259. main->rowgroups_avail = (JDIMENSION) ( ( rows_left - 1 ) / rgroup + 1 );
  260. }
  261. /* Duplicate the last real sample row rgroup*2 times; this pads out the
  262. * last partial rowgroup and ensures at least one full rowgroup of context.
  263. */
  264. xbuf = main->xbuffer[main->whichptr][ci];
  265. for ( i = 0; i < rgroup * 2; i++ ) {
  266. xbuf[rows_left + i] = xbuf[rows_left - 1];
  267. }
  268. }
  269. }
  270. /*
  271. * Initialize for a processing pass.
  272. */
  273. METHODDEF void
  274. start_pass_main( j_decompress_ptr cinfo, J_BUF_MODE pass_mode ) {
  275. my_main_ptr main = (my_main_ptr) cinfo->main;
  276. switch ( pass_mode ) {
  277. case JBUF_PASS_THRU:
  278. if ( cinfo->upsample->need_context_rows ) {
  279. main->pub.process_data = process_data_context_main;
  280. make_funny_pointers( cinfo );/* Create the xbuffer[] lists */
  281. main->whichptr = 0;/* Read first iMCU row into xbuffer[0] */
  282. main->context_state = CTX_PREPARE_FOR_IMCU;
  283. main->iMCU_row_ctr = 0;
  284. } else {
  285. /* Simple case with no context needed */
  286. main->pub.process_data = process_data_simple_main;
  287. }
  288. main->buffer_full = FALSE;/* Mark buffer empty */
  289. main->rowgroup_ctr = 0;
  290. break;
  291. #ifdef QUANT_2PASS_SUPPORTED
  292. case JBUF_CRANK_DEST:
  293. /* For last pass of 2-pass quantization, just crank the postprocessor */
  294. main->pub.process_data = process_data_crank_post;
  295. break;
  296. #endif
  297. default:
  298. ERREXIT( cinfo, JERR_BAD_BUFFER_MODE );
  299. break;
  300. }
  301. }
  302. /*
  303. * Process some data.
  304. * This handles the simple case where no context is required.
  305. */
  306. METHODDEF void
  307. process_data_simple_main( j_decompress_ptr cinfo,
  308. JSAMPARRAY output_buf, JDIMENSION * out_row_ctr,
  309. JDIMENSION out_rows_avail ) {
  310. my_main_ptr main = (my_main_ptr) cinfo->main;
  311. JDIMENSION rowgroups_avail;
  312. /* Read input data if we haven't filled the main buffer yet */
  313. if ( !main->buffer_full ) {
  314. if ( !( *cinfo->coef->decompress_data )( cinfo, main->buffer ) ) {
  315. return;
  316. } /* suspension forced, can do nothing more */
  317. main->buffer_full = TRUE;/* OK, we have an iMCU row to work with */
  318. }
  319. /* There are always min_DCT_scaled_size row groups in an iMCU row. */
  320. rowgroups_avail = (JDIMENSION) cinfo->min_DCT_scaled_size;
  321. /* Note: at the bottom of the image, we may pass extra garbage row groups
  322. * to the postprocessor. The postprocessor has to check for bottom
  323. * of image anyway (at row resolution), so no point in us doing it too.
  324. */
  325. /* Feed the postprocessor */
  326. ( *cinfo->post->post_process_data )( cinfo, main->buffer,
  327. &main->rowgroup_ctr, rowgroups_avail,
  328. output_buf, out_row_ctr, out_rows_avail );
  329. /* Has postprocessor consumed all the data yet? If so, mark buffer empty */
  330. if ( main->rowgroup_ctr >= rowgroups_avail ) {
  331. main->buffer_full = FALSE;
  332. main->rowgroup_ctr = 0;
  333. }
  334. }
  335. /*
  336. * Process some data.
  337. * This handles the case where context rows must be provided.
  338. */
  339. METHODDEF void
  340. process_data_context_main( j_decompress_ptr cinfo,
  341. JSAMPARRAY output_buf, JDIMENSION * out_row_ctr,
  342. JDIMENSION out_rows_avail ) {
  343. my_main_ptr main = (my_main_ptr) cinfo->main;
  344. /* Read input data if we haven't filled the main buffer yet */
  345. if ( !main->buffer_full ) {
  346. if ( !( *cinfo->coef->decompress_data )( cinfo,
  347. main->xbuffer[main->whichptr] ) ) {
  348. return;
  349. } /* suspension forced, can do nothing more */
  350. main->buffer_full = TRUE;/* OK, we have an iMCU row to work with */
  351. main->iMCU_row_ctr++; /* count rows received */
  352. }
  353. /* Postprocessor typically will not swallow all the input data it is handed
  354. * in one call (due to filling the output buffer first). Must be prepared
  355. * to exit and restart. This switch lets us keep track of how far we got.
  356. * Note that each case falls through to the next on successful completion.
  357. */
  358. switch ( main->context_state ) {
  359. case CTX_POSTPONED_ROW:
  360. /* Call postprocessor using previously set pointers for postponed row */
  361. ( *cinfo->post->post_process_data )( cinfo, main->xbuffer[main->whichptr],
  362. &main->rowgroup_ctr, main->rowgroups_avail,
  363. output_buf, out_row_ctr, out_rows_avail );
  364. if ( main->rowgroup_ctr < main->rowgroups_avail ) {
  365. return;
  366. } /* Need to suspend */
  367. main->context_state = CTX_PREPARE_FOR_IMCU;
  368. if ( *out_row_ctr >= out_rows_avail ) {
  369. return;
  370. } /* Postprocessor exactly filled output buf */
  371. /*FALLTHROUGH*/
  372. case CTX_PREPARE_FOR_IMCU:
  373. /* Prepare to process first M-1 row groups of this iMCU row */
  374. main->rowgroup_ctr = 0;
  375. main->rowgroups_avail = (JDIMENSION) ( cinfo->min_DCT_scaled_size - 1 );
  376. /* Check for bottom of image: if so, tweak pointers to "duplicate"
  377. * the last sample row, and adjust rowgroups_avail to ignore padding rows.
  378. */
  379. if ( main->iMCU_row_ctr == cinfo->total_iMCU_rows ) {
  380. set_bottom_pointers( cinfo );
  381. }
  382. main->context_state = CTX_PROCESS_IMCU;
  383. /*FALLTHROUGH*/
  384. case CTX_PROCESS_IMCU:
  385. /* Call postprocessor using previously set pointers */
  386. ( *cinfo->post->post_process_data )( cinfo, main->xbuffer[main->whichptr],
  387. &main->rowgroup_ctr, main->rowgroups_avail,
  388. output_buf, out_row_ctr, out_rows_avail );
  389. if ( main->rowgroup_ctr < main->rowgroups_avail ) {
  390. return;
  391. } /* Need to suspend */
  392. /* After the first iMCU, change wraparound pointers to normal state */
  393. if ( main->iMCU_row_ctr == 1 ) {
  394. set_wraparound_pointers( cinfo );
  395. }
  396. /* Prepare to load new iMCU row using other xbuffer list */
  397. main->whichptr ^= 1;/* 0=>1 or 1=>0 */
  398. main->buffer_full = FALSE;
  399. /* Still need to process last row group of this iMCU row, */
  400. /* which is saved at index M+1 of the other xbuffer */
  401. main->rowgroup_ctr = (JDIMENSION) ( cinfo->min_DCT_scaled_size + 1 );
  402. main->rowgroups_avail = (JDIMENSION) ( cinfo->min_DCT_scaled_size + 2 );
  403. main->context_state = CTX_POSTPONED_ROW;
  404. }
  405. }
  406. /*
  407. * Process some data.
  408. * Final pass of two-pass quantization: just call the postprocessor.
  409. * Source data will be the postprocessor controller's internal buffer.
  410. */
  411. #ifdef QUANT_2PASS_SUPPORTED
  412. METHODDEF void
  413. process_data_crank_post( j_decompress_ptr cinfo,
  414. JSAMPARRAY output_buf, JDIMENSION * out_row_ctr,
  415. JDIMENSION out_rows_avail ) {
  416. ( *cinfo->post->post_process_data )( cinfo, (JSAMPIMAGE) NULL,
  417. (JDIMENSION *) NULL, (JDIMENSION) 0,
  418. output_buf, out_row_ctr, out_rows_avail );
  419. }
  420. #endif /* QUANT_2PASS_SUPPORTED */
  421. /*
  422. * Initialize main buffer controller.
  423. */
  424. GLOBAL void
  425. jinit_d_main_controller( j_decompress_ptr cinfo, boolean need_full_buffer ) {
  426. my_main_ptr main;
  427. int ci, rgroup, ngroups;
  428. jpeg_component_info * compptr;
  429. main = (my_main_ptr)
  430. ( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE,
  431. SIZEOF( my_main_controller ) );
  432. cinfo->main = (struct jpeg_d_main_controller *) main;
  433. main->pub.start_pass = start_pass_main;
  434. if ( need_full_buffer ) {/* shouldn't happen */
  435. ERREXIT( cinfo, JERR_BAD_BUFFER_MODE );
  436. }
  437. /* Allocate the workspace.
  438. * ngroups is the number of row groups we need.
  439. */
  440. if ( cinfo->upsample->need_context_rows ) {
  441. if ( cinfo->min_DCT_scaled_size < 2 ) {/* unsupported, see comments above */
  442. ERREXIT( cinfo, JERR_NOTIMPL );
  443. }
  444. alloc_funny_pointers( cinfo );/* Alloc space for xbuffer[] lists */
  445. ngroups = cinfo->min_DCT_scaled_size + 2;
  446. } else {
  447. ngroups = cinfo->min_DCT_scaled_size;
  448. }
  449. for ( ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
  450. ci++, compptr++ ) {
  451. rgroup = ( compptr->v_samp_factor * compptr->DCT_scaled_size ) /
  452. cinfo->min_DCT_scaled_size; /* height of a row group of component */
  453. main->buffer[ci] = ( *cinfo->mem->alloc_sarray )
  454. ( (j_common_ptr) cinfo, JPOOL_IMAGE,
  455. compptr->width_in_blocks * compptr->DCT_scaled_size,
  456. (JDIMENSION) ( rgroup * ngroups ) );
  457. }
  458. }