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