4 * Copyright (C) 1994-1996, Thomas G. Lane.
5 * Modified 2002-2020 by Guido Vollbeding.
6 * This file is part of the Independent JPEG Group's software.
7 * For conditions of distribution and use, see the accompanying README file.
9 * This file contains the main buffer controller for decompression.
10 * The main buffer lies between the JPEG decompressor proper and the
11 * post-processor; it holds downsampled data in the JPEG colorspace.
13 * Note that this code is bypassed in raw-data mode, since the application
14 * supplies the equivalent of the main buffer in that case.
17 #define JPEG_INTERNALS
23 * In the current system design, the main buffer need never be a full-image
24 * buffer; any full-height buffers will be found inside the coefficient or
25 * postprocessing controllers. Nonetheless, the main controller is not
26 * trivial. Its responsibility is to provide context rows for upsampling/
27 * rescaling, and doing this in an efficient fashion is a bit tricky.
29 * Postprocessor input data is counted in "row groups". A row group is
30 * defined to be (v_samp_factor * DCT_v_scaled_size / min_DCT_v_scaled_size)
31 * sample rows of each component. (We require DCT_scaled_size values to be
32 * chosen such that these numbers are integers. In practice DCT_scaled_size
33 * values will likely be powers of two, so we actually have the stronger
34 * condition that DCT_scaled_size / min_DCT_scaled_size is an integer.)
35 * Upsampling will typically produce max_v_samp_factor pixel rows from each
36 * row group (times any additional scale factor that the upsampler is
39 * The coefficient controller will deliver data to us one iMCU row at a time;
40 * each iMCU row contains v_samp_factor * DCT_v_scaled_size sample rows, or
41 * exactly min_DCT_v_scaled_size row groups. (This amount of data corresponds
42 * to one row of MCUs when the image is fully interleaved.) Note that the
43 * number of sample rows varies across components, but the number of row
44 * groups does not. Some garbage sample rows may be included in the last iMCU
45 * row at the bottom of the image.
47 * Depending on the vertical scaling algorithm used, the upsampler may need
48 * access to the sample row(s) above and below its current input row group.
49 * The upsampler is required to set need_context_rows TRUE at global selection
50 * time if so. When need_context_rows is FALSE, this controller can simply
51 * obtain one iMCU row at a time from the coefficient controller and dole it
52 * out as row groups to the postprocessor.
54 * When need_context_rows is TRUE, this controller guarantees that the buffer
55 * passed to postprocessing contains at least one row group's worth of samples
56 * above and below the row group(s) being processed. Note that the context
57 * rows "above" the first passed row group appear at negative row offsets in
58 * the passed buffer. At the top and bottom of the image, the required
59 * context rows are manufactured by duplicating the first or last real sample
60 * row; this avoids having special cases in the upsampling inner loops.
62 * The amount of context is fixed at one row group just because that's a
63 * convenient number for this controller to work with. The existing
64 * upsamplers really only need one sample row of context. An upsampler
65 * supporting arbitrary output rescaling might wish for more than one row
66 * group of context when shrinking the image; tough, we don't handle that.
67 * (This is justified by the assumption that downsizing will be handled mostly
68 * by adjusting the DCT_scaled_size values, so that the actual scale factor at
69 * the upsample step needn't be much less than one.)
71 * To provide the desired context, we have to retain the last two row groups
72 * of one iMCU row while reading in the next iMCU row. (The last row group
73 * can't be processed until we have another row group for its below-context,
74 * and so we have to save the next-to-last group too for its above-context.)
75 * We could do this most simply by copying data around in our buffer, but
76 * that'd be very slow. We can avoid copying any data by creating a rather
77 * strange pointer structure. Here's how it works. We allocate a workspace
78 * consisting of M+2 row groups (where M = min_DCT_v_scaled_size is the number
79 * of row groups per iMCU row). We create two sets of redundant pointers to
80 * the workspace. Labeling the physical row groups 0 to M+1, the synthesized
81 * pointer lists look like this:
83 * master pointer --> 0 master pointer --> 0
92 * We read alternate iMCU rows using each master pointer; thus the last two
93 * row groups of the previous iMCU row remain un-overwritten in the workspace.
94 * The pointer lists are set up so that the required context rows appear to
95 * be adjacent to the proper places when we pass the pointer lists to the
98 * The above pictures describe the normal state of the pointer lists.
99 * At top and bottom of the image, we diddle the pointer lists to duplicate
100 * the first or last sample row as necessary (this is cheaper than copying
101 * sample rows around).
103 * This scheme breaks down if M < 2, ie, min_DCT_v_scaled_size is 1. In that
104 * situation each iMCU row provides only one row group so the buffering logic
105 * must be different (eg, we must read two iMCU rows before we can emit the
106 * first row group). For now, we simply do not support providing context
107 * rows when min_DCT_v_scaled_size is 1. That combination seems unlikely to
108 * be worth providing --- if someone wants a 1/8th-size preview, they probably
109 * want it quick and dirty, so a context-free upsampler is sufficient.
113 /* Private buffer controller object */
116 struct jpeg_d_main_controller pub
; /* public fields */
118 /* Pointer to allocated workspace (M or M+2 row groups). */
119 JSAMPARRAY buffer
[MAX_COMPONENTS
];
121 JDIMENSION rowgroup_ctr
; /* counts row groups output to postprocessor */
122 JDIMENSION rowgroups_avail
; /* row groups available to postprocessor */
124 /* Remaining fields are only used in the context case. */
126 boolean buffer_full
; /* Have we gotten an iMCU row from decoder? */
128 /* These are the master pointers to the funny-order pointer lists. */
129 JSAMPIMAGE xbuffer
[2]; /* pointers to weird pointer lists */
131 int whichptr
; /* indicates which pointer set is now in use */
132 int context_state
; /* process_data state machine status */
133 JDIMENSION iMCU_row_ctr
; /* counts iMCU rows to detect image top/bot */
134 } my_main_controller
;
136 typedef my_main_controller
* my_main_ptr
;
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 */
144 /* Forward declarations */
145 METHODDEF(void) process_data_simple_main
146 JPP((j_decompress_ptr cinfo
, JSAMPARRAY output_buf
,
147 JDIMENSION
*out_row_ctr
, JDIMENSION out_rows_avail
));
148 METHODDEF(void) process_data_context_main
149 JPP((j_decompress_ptr cinfo
, JSAMPARRAY output_buf
,
150 JDIMENSION
*out_row_ctr
, JDIMENSION out_rows_avail
));
151 #ifdef QUANT_2PASS_SUPPORTED
152 METHODDEF(void) process_data_crank_post
153 JPP((j_decompress_ptr cinfo
, JSAMPARRAY output_buf
,
154 JDIMENSION
*out_row_ctr
, JDIMENSION out_rows_avail
));
159 alloc_funny_pointers (j_decompress_ptr cinfo
)
160 /* Allocate space for the funny pointer lists.
161 * This is done only once, not once per pass.
164 my_main_ptr mainp
= (my_main_ptr
) cinfo
->main
;
166 int M
= cinfo
->min_DCT_v_scaled_size
;
167 jpeg_component_info
*compptr
;
170 /* Get top-level space for component array pointers.
171 * We alloc both arrays with one call to save a few cycles.
173 mainp
->xbuffer
[0] = (JSAMPIMAGE
) (*cinfo
->mem
->alloc_small
)
174 ((j_common_ptr
) cinfo
, JPOOL_IMAGE
,
175 cinfo
->num_components
* 2 * SIZEOF(JSAMPARRAY
));
176 mainp
->xbuffer
[1] = mainp
->xbuffer
[0] + cinfo
->num_components
;
178 for (ci
= 0, compptr
= cinfo
->comp_info
; ci
< cinfo
->num_components
;
180 if (! compptr
->component_needed
)
181 continue; /* skip uninteresting component */
182 rgroup
= (compptr
->v_samp_factor
* compptr
->DCT_v_scaled_size
) /
183 cinfo
->min_DCT_v_scaled_size
; /* height of a row group of component */
184 /* Get space for pointer lists --- M+4 row groups in each list.
185 * We alloc both pointer lists with one call to save a few cycles.
187 xbuf
= (JSAMPARRAY
) (*cinfo
->mem
->alloc_small
) ((j_common_ptr
) cinfo
,
188 JPOOL_IMAGE
, 2 * (rgroup
* (M
+ 4)) * SIZEOF(JSAMPROW
));
189 xbuf
+= rgroup
; /* want one row group at negative offsets */
190 mainp
->xbuffer
[0][ci
] = xbuf
;
191 xbuf
+= rgroup
* (M
+ 4);
192 mainp
->xbuffer
[1][ci
] = xbuf
;
198 make_funny_pointers (j_decompress_ptr cinfo
)
199 /* Create the funny pointer lists discussed in the comments above.
200 * The actual workspace is already allocated (in mainp->buffer),
201 * and the space for the pointer lists is allocated too.
202 * This routine just fills in the curiously ordered lists.
203 * This will be repeated at the beginning of each pass.
206 my_main_ptr mainp
= (my_main_ptr
) cinfo
->main
;
208 int M
= cinfo
->min_DCT_v_scaled_size
;
209 jpeg_component_info
*compptr
;
210 JSAMPARRAY buf
, xbuf0
, xbuf1
;
212 for (ci
= 0, compptr
= cinfo
->comp_info
; ci
< cinfo
->num_components
;
214 if (! compptr
->component_needed
)
215 continue; /* skip uninteresting component */
216 rgroup
= (compptr
->v_samp_factor
* compptr
->DCT_v_scaled_size
) /
217 cinfo
->min_DCT_v_scaled_size
; /* height of a row group of component */
218 xbuf0
= mainp
->xbuffer
[0][ci
];
219 xbuf1
= mainp
->xbuffer
[1][ci
];
220 /* First copy the workspace pointers as-is */
221 buf
= mainp
->buffer
[ci
];
222 for (i
= 0; i
< rgroup
* (M
+ 2); i
++) {
223 xbuf0
[i
] = xbuf1
[i
] = buf
[i
];
225 /* In the second list, put the last four row groups in swapped order */
226 for (i
= 0; i
< rgroup
* 2; i
++) {
227 xbuf1
[rgroup
*(M
-2) + i
] = buf
[rgroup
*M
+ i
];
228 xbuf1
[rgroup
*M
+ i
] = buf
[rgroup
*(M
-2) + i
];
230 /* The wraparound pointers at top and bottom will be filled later
231 * (see set_wraparound_pointers, below). Initially we want the "above"
232 * pointers to duplicate the first actual data line. This only needs
233 * to happen in xbuffer[0].
235 for (i
= 0; i
< rgroup
; i
++) {
236 xbuf0
[i
- rgroup
] = xbuf0
[0];
243 set_wraparound_pointers (j_decompress_ptr cinfo
)
244 /* Set up the "wraparound" pointers at top and bottom of the pointer lists.
245 * This changes the pointer list state from top-of-image to the normal state.
248 my_main_ptr mainp
= (my_main_ptr
) cinfo
->main
;
250 int M
= cinfo
->min_DCT_v_scaled_size
;
251 jpeg_component_info
*compptr
;
252 JSAMPARRAY xbuf0
, xbuf1
;
254 for (ci
= 0, compptr
= cinfo
->comp_info
; ci
< cinfo
->num_components
;
256 if (! compptr
->component_needed
)
257 continue; /* skip uninteresting component */
258 rgroup
= (compptr
->v_samp_factor
* compptr
->DCT_v_scaled_size
) /
259 cinfo
->min_DCT_v_scaled_size
; /* height of a row group of component */
260 xbuf0
= mainp
->xbuffer
[0][ci
];
261 xbuf1
= mainp
->xbuffer
[1][ci
];
262 for (i
= 0; i
< rgroup
; i
++) {
263 xbuf0
[i
- rgroup
] = xbuf0
[rgroup
*(M
+1) + i
];
264 xbuf1
[i
- rgroup
] = xbuf1
[rgroup
*(M
+1) + i
];
265 xbuf0
[rgroup
*(M
+2) + i
] = xbuf0
[i
];
266 xbuf1
[rgroup
*(M
+2) + i
] = xbuf1
[i
];
273 set_bottom_pointers (j_decompress_ptr cinfo
)
274 /* Change the pointer lists to duplicate the last sample row at the bottom
275 * of the image. whichptr indicates which xbuffer holds the final iMCU row.
276 * Also sets rowgroups_avail to indicate number of nondummy row groups in row.
279 my_main_ptr mainp
= (my_main_ptr
) cinfo
->main
;
280 int ci
, i
, rgroup
, iMCUheight
, rows_left
;
281 jpeg_component_info
*compptr
;
284 for (ci
= 0, compptr
= cinfo
->comp_info
; ci
< cinfo
->num_components
;
286 if (! compptr
->component_needed
)
287 continue; /* skip uninteresting component */
288 /* Count sample rows in one iMCU row and in one row group */
289 iMCUheight
= compptr
->v_samp_factor
* compptr
->DCT_v_scaled_size
;
290 rgroup
= iMCUheight
/ cinfo
->min_DCT_v_scaled_size
;
291 /* Count nondummy sample rows remaining for this component */
292 rows_left
= (int) (compptr
->downsampled_height
% (JDIMENSION
) iMCUheight
);
293 if (rows_left
== 0) rows_left
= iMCUheight
;
294 /* Count nondummy row groups. Should get same answer for each component,
295 * so we need only do it once.
298 mainp
->rowgroups_avail
= (JDIMENSION
) ((rows_left
-1) / rgroup
+ 1);
300 /* Duplicate the last real sample row rgroup*2 times; this pads out the
301 * last partial rowgroup and ensures at least one full rowgroup of context.
303 xbuf
= mainp
->xbuffer
[mainp
->whichptr
][ci
];
304 for (i
= 0; i
< rgroup
* 2; i
++) {
305 xbuf
[rows_left
+ i
] = xbuf
[rows_left
-1];
312 * Initialize for a processing pass.
316 start_pass_main (j_decompress_ptr cinfo
, J_BUF_MODE pass_mode
)
318 my_main_ptr mainp
= (my_main_ptr
) cinfo
->main
;
322 if (cinfo
->upsample
->need_context_rows
) {
323 mainp
->pub
.process_data
= process_data_context_main
;
324 make_funny_pointers(cinfo
); /* Create the xbuffer[] lists */
325 mainp
->whichptr
= 0; /* Read first iMCU row into xbuffer[0] */
326 mainp
->context_state
= CTX_PREPARE_FOR_IMCU
;
327 mainp
->iMCU_row_ctr
= 0;
328 mainp
->buffer_full
= FALSE
; /* Mark buffer empty */
330 /* Simple case with no context needed */
331 mainp
->pub
.process_data
= process_data_simple_main
;
332 mainp
->rowgroup_ctr
= mainp
->rowgroups_avail
; /* Mark buffer empty */
335 #ifdef QUANT_2PASS_SUPPORTED
336 case JBUF_CRANK_DEST
:
337 /* For last pass of 2-pass quantization, just crank the postprocessor */
338 mainp
->pub
.process_data
= process_data_crank_post
;
342 ERREXIT(cinfo
, JERR_BAD_BUFFER_MODE
);
349 * This handles the simple case where no context is required.
353 process_data_simple_main (j_decompress_ptr cinfo
, JSAMPARRAY output_buf
,
354 JDIMENSION
*out_row_ctr
, JDIMENSION out_rows_avail
)
356 my_main_ptr mainp
= (my_main_ptr
) cinfo
->main
;
358 /* Read input data if we haven't filled the main buffer yet */
359 if (mainp
->rowgroup_ctr
>= mainp
->rowgroups_avail
) {
360 if (! (*cinfo
->coef
->decompress_data
) (cinfo
, mainp
->buffer
))
361 return; /* suspension forced, can do nothing more */
362 mainp
->rowgroup_ctr
= 0; /* OK, we have an iMCU row to work with */
365 /* Note: at the bottom of the image, we may pass extra garbage row groups
366 * to the postprocessor. The postprocessor has to check for bottom
367 * of image anyway (at row resolution), so no point in us doing it too.
370 /* Feed the postprocessor */
371 (*cinfo
->post
->post_process_data
) (cinfo
, mainp
->buffer
,
372 &mainp
->rowgroup_ctr
, mainp
->rowgroups_avail
,
373 output_buf
, out_row_ctr
, out_rows_avail
);
379 * This handles the case where context rows must be provided.
383 process_data_context_main (j_decompress_ptr cinfo
, JSAMPARRAY output_buf
,
384 JDIMENSION
*out_row_ctr
, JDIMENSION out_rows_avail
)
386 my_main_ptr mainp
= (my_main_ptr
) cinfo
->main
;
388 /* Read input data if we haven't filled the main buffer yet */
389 if (! mainp
->buffer_full
) {
390 if (! (*cinfo
->coef
->decompress_data
) (cinfo
,
391 mainp
->xbuffer
[mainp
->whichptr
]))
392 return; /* suspension forced, can do nothing more */
393 mainp
->buffer_full
= TRUE
; /* OK, we have an iMCU row to work with */
394 mainp
->iMCU_row_ctr
++; /* count rows received */
397 /* Postprocessor typically will not swallow all the input data it is handed
398 * in one call (due to filling the output buffer first). Must be prepared
399 * to exit and restart. This switch lets us keep track of how far we got.
400 * Note that each case falls through to the next on successful completion.
402 switch (mainp
->context_state
) {
403 case CTX_POSTPONED_ROW
:
404 /* Call postprocessor using previously set pointers for postponed row */
405 (*cinfo
->post
->post_process_data
) (cinfo
, mainp
->xbuffer
[mainp
->whichptr
],
406 &mainp
->rowgroup_ctr
, mainp
->rowgroups_avail
,
407 output_buf
, out_row_ctr
, out_rows_avail
);
408 if (mainp
->rowgroup_ctr
< mainp
->rowgroups_avail
)
409 return; /* Need to suspend */
410 mainp
->context_state
= CTX_PREPARE_FOR_IMCU
;
411 if (*out_row_ctr
>= out_rows_avail
)
412 return; /* Postprocessor exactly filled output buf */
414 case CTX_PREPARE_FOR_IMCU
:
415 /* Prepare to process first M-1 row groups of this iMCU row */
416 mainp
->rowgroup_ctr
= 0;
417 mainp
->rowgroups_avail
= (JDIMENSION
) (cinfo
->min_DCT_v_scaled_size
- 1);
418 /* Check for bottom of image: if so, tweak pointers to "duplicate"
419 * the last sample row, and adjust rowgroups_avail to ignore padding rows.
421 if (mainp
->iMCU_row_ctr
== cinfo
->total_iMCU_rows
)
422 set_bottom_pointers(cinfo
);
423 mainp
->context_state
= CTX_PROCESS_IMCU
;
425 case CTX_PROCESS_IMCU
:
426 /* Call postprocessor using previously set pointers */
427 (*cinfo
->post
->post_process_data
) (cinfo
, mainp
->xbuffer
[mainp
->whichptr
],
428 &mainp
->rowgroup_ctr
, mainp
->rowgroups_avail
,
429 output_buf
, out_row_ctr
, out_rows_avail
);
430 if (mainp
->rowgroup_ctr
< mainp
->rowgroups_avail
)
431 return; /* Need to suspend */
432 /* After the first iMCU, change wraparound pointers to normal state */
433 if (mainp
->iMCU_row_ctr
== 1)
434 set_wraparound_pointers(cinfo
);
435 /* Prepare to load new iMCU row using other xbuffer list */
436 mainp
->whichptr
^= 1; /* 0=>1 or 1=>0 */
437 mainp
->buffer_full
= FALSE
;
438 /* Still need to process last row group of this iMCU row, */
439 /* which is saved at index M+1 of the other xbuffer */
440 mainp
->rowgroup_ctr
= (JDIMENSION
) (cinfo
->min_DCT_v_scaled_size
+ 1);
441 mainp
->rowgroups_avail
= (JDIMENSION
) (cinfo
->min_DCT_v_scaled_size
+ 2);
442 mainp
->context_state
= CTX_POSTPONED_ROW
;
449 * Final pass of two-pass quantization: just call the postprocessor.
450 * Source data will be the postprocessor controller's internal buffer.
453 #ifdef QUANT_2PASS_SUPPORTED
456 process_data_crank_post (j_decompress_ptr cinfo
, JSAMPARRAY output_buf
,
457 JDIMENSION
*out_row_ctr
, JDIMENSION out_rows_avail
)
459 (*cinfo
->post
->post_process_data
) (cinfo
, (JSAMPIMAGE
) NULL
,
460 (JDIMENSION
*) NULL
, (JDIMENSION
) 0,
461 output_buf
, out_row_ctr
, out_rows_avail
);
464 #endif /* QUANT_2PASS_SUPPORTED */
468 * Initialize main buffer controller.
472 jinit_d_main_controller (j_decompress_ptr cinfo
, boolean need_full_buffer
)
475 int ci
, rgroup
, ngroups
;
476 jpeg_component_info
*compptr
;
478 mainp
= (my_main_ptr
) (*cinfo
->mem
->alloc_small
)
479 ((j_common_ptr
) cinfo
, JPOOL_IMAGE
, SIZEOF(my_main_controller
));
480 cinfo
->main
= &mainp
->pub
;
481 mainp
->pub
.start_pass
= start_pass_main
;
483 if (need_full_buffer
) /* shouldn't happen */
484 ERREXIT(cinfo
, JERR_BAD_BUFFER_MODE
);
486 /* Allocate the workspace.
487 * ngroups is the number of row groups we need.
489 if (cinfo
->upsample
->need_context_rows
) {
490 if (cinfo
->min_DCT_v_scaled_size
< 2) /* unsupported, see comments above */
491 ERREXIT(cinfo
, JERR_NOTIMPL
);
492 alloc_funny_pointers(cinfo
); /* Alloc space for xbuffer[] lists */
493 ngroups
= cinfo
->min_DCT_v_scaled_size
+ 2;
495 /* There are always min_DCT_v_scaled_size row groups in an iMCU row. */
496 ngroups
= cinfo
->min_DCT_v_scaled_size
;
497 mainp
->rowgroups_avail
= (JDIMENSION
) ngroups
;
500 for (ci
= 0, compptr
= cinfo
->comp_info
; ci
< cinfo
->num_components
;
502 if (! compptr
->component_needed
)
503 continue; /* skip uninteresting component */
504 rgroup
= (compptr
->v_samp_factor
* compptr
->DCT_v_scaled_size
) /
505 cinfo
->min_DCT_v_scaled_size
; /* height of a row group of component */
506 mainp
->buffer
[ci
] = (*cinfo
->mem
->alloc_sarray
)
507 ((j_common_ptr
) cinfo
, JPOOL_IMAGE
,
508 compptr
->width_in_blocks
* ((JDIMENSION
) compptr
->DCT_h_scaled_size
),
509 (JDIMENSION
) (rgroup
* ngroups
));