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
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.
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.
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.
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
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.
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.
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.
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.)
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:
84 * master pointer --> 0 master pointer --> 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
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).
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.
114 /* Forward declarations */
115 METHODDEF(void) process_data_simple_main(j_decompress_ptr cinfo
,
116 JSAMPARRAY output_buf
,
117 JDIMENSION
*out_row_ctr
,
118 JDIMENSION out_rows_avail
);
119 METHODDEF(void) process_data_context_main(j_decompress_ptr cinfo
,
120 JSAMPARRAY output_buf
,
121 JDIMENSION
*out_row_ctr
,
122 JDIMENSION out_rows_avail
);
123 #ifdef QUANT_2PASS_SUPPORTED
124 METHODDEF(void) process_data_crank_post(j_decompress_ptr cinfo
,
125 JSAMPARRAY output_buf
,
126 JDIMENSION
*out_row_ctr
,
127 JDIMENSION out_rows_avail
);
132 alloc_funny_pointers(j_decompress_ptr cinfo
)
133 /* Allocate space for the funny pointer lists.
134 * This is done only once, not once per pass.
137 my_main_ptr main_ptr
= (my_main_ptr
)cinfo
->main
;
139 int M
= cinfo
->_min_DCT_scaled_size
;
140 jpeg_component_info
*compptr
;
143 /* Get top-level space for component array pointers.
144 * We alloc both arrays with one call to save a few cycles.
146 main_ptr
->xbuffer
[0] = (JSAMPIMAGE
)
147 (*cinfo
->mem
->alloc_small
) ((j_common_ptr
)cinfo
, JPOOL_IMAGE
,
148 cinfo
->num_components
* 2 * sizeof(JSAMPARRAY
));
149 main_ptr
->xbuffer
[1] = main_ptr
->xbuffer
[0] + cinfo
->num_components
;
151 for (ci
= 0, compptr
= cinfo
->comp_info
; ci
< cinfo
->num_components
;
153 rgroup
= (compptr
->v_samp_factor
* compptr
->_DCT_scaled_size
) /
154 cinfo
->_min_DCT_scaled_size
; /* height of a row group of component */
155 /* Get space for pointer lists --- M+4 row groups in each list.
156 * We alloc both pointer lists with one call to save a few cycles.
159 (*cinfo
->mem
->alloc_small
) ((j_common_ptr
)cinfo
, JPOOL_IMAGE
,
160 2 * (rgroup
* (M
+ 4)) * sizeof(JSAMPROW
));
161 xbuf
+= rgroup
; /* want one row group at negative offsets */
162 main_ptr
->xbuffer
[0][ci
] = xbuf
;
163 xbuf
+= rgroup
* (M
+ 4);
164 main_ptr
->xbuffer
[1][ci
] = xbuf
;
170 make_funny_pointers(j_decompress_ptr cinfo
)
171 /* Create the funny pointer lists discussed in the comments above.
172 * The actual workspace is already allocated (in main_ptr->buffer),
173 * and the space for the pointer lists is allocated too.
174 * This routine just fills in the curiously ordered lists.
175 * This will be repeated at the beginning of each pass.
178 my_main_ptr main_ptr
= (my_main_ptr
)cinfo
->main
;
180 int M
= cinfo
->_min_DCT_scaled_size
;
181 jpeg_component_info
*compptr
;
182 JSAMPARRAY buf
, xbuf0
, xbuf1
;
184 for (ci
= 0, compptr
= cinfo
->comp_info
; ci
< cinfo
->num_components
;
186 rgroup
= (compptr
->v_samp_factor
* compptr
->_DCT_scaled_size
) /
187 cinfo
->_min_DCT_scaled_size
; /* height of a row group of component */
188 xbuf0
= main_ptr
->xbuffer
[0][ci
];
189 xbuf1
= main_ptr
->xbuffer
[1][ci
];
190 /* First copy the workspace pointers as-is */
191 buf
= main_ptr
->buffer
[ci
];
192 for (i
= 0; i
< rgroup
* (M
+ 2); i
++) {
193 xbuf0
[i
] = xbuf1
[i
] = buf
[i
];
195 /* In the second list, put the last four row groups in swapped order */
196 for (i
= 0; i
< rgroup
* 2; i
++) {
197 xbuf1
[rgroup
* (M
- 2) + i
] = buf
[rgroup
* M
+ i
];
198 xbuf1
[rgroup
* M
+ i
] = buf
[rgroup
* (M
- 2) + i
];
200 /* The wraparound pointers at top and bottom will be filled later
201 * (see set_wraparound_pointers, below). Initially we want the "above"
202 * pointers to duplicate the first actual data line. This only needs
203 * to happen in xbuffer[0].
205 for (i
= 0; i
< rgroup
; i
++) {
206 xbuf0
[i
- rgroup
] = xbuf0
[0];
213 set_bottom_pointers(j_decompress_ptr cinfo
)
214 /* Change the pointer lists to duplicate the last sample row at the bottom
215 * of the image. whichptr indicates which xbuffer holds the final iMCU row.
216 * Also sets rowgroups_avail to indicate number of nondummy row groups in row.
219 my_main_ptr main_ptr
= (my_main_ptr
)cinfo
->main
;
220 int ci
, i
, rgroup
, iMCUheight
, rows_left
;
221 jpeg_component_info
*compptr
;
224 for (ci
= 0, compptr
= cinfo
->comp_info
; ci
< cinfo
->num_components
;
226 /* Count sample rows in one iMCU row and in one row group */
227 iMCUheight
= compptr
->v_samp_factor
* compptr
->_DCT_scaled_size
;
228 rgroup
= iMCUheight
/ cinfo
->_min_DCT_scaled_size
;
229 /* Count nondummy sample rows remaining for this component */
230 rows_left
= (int)(compptr
->downsampled_height
% (JDIMENSION
)iMCUheight
);
231 if (rows_left
== 0) rows_left
= iMCUheight
;
232 /* Count nondummy row groups. Should get same answer for each component,
233 * so we need only do it once.
236 main_ptr
->rowgroups_avail
= (JDIMENSION
)((rows_left
- 1) / rgroup
+ 1);
238 /* Duplicate the last real sample row rgroup*2 times; this pads out the
239 * last partial rowgroup and ensures at least one full rowgroup of context.
241 xbuf
= main_ptr
->xbuffer
[main_ptr
->whichptr
][ci
];
242 for (i
= 0; i
< rgroup
* 2; i
++) {
243 xbuf
[rows_left
+ i
] = xbuf
[rows_left
- 1];
250 * Initialize for a processing pass.
254 start_pass_main(j_decompress_ptr cinfo
, J_BUF_MODE pass_mode
)
256 my_main_ptr main_ptr
= (my_main_ptr
)cinfo
->main
;
260 if (cinfo
->upsample
->need_context_rows
) {
261 main_ptr
->pub
.process_data
= process_data_context_main
;
262 make_funny_pointers(cinfo
); /* Create the xbuffer[] lists */
263 main_ptr
->whichptr
= 0; /* Read first iMCU row into xbuffer[0] */
264 main_ptr
->context_state
= CTX_PREPARE_FOR_IMCU
;
265 main_ptr
->iMCU_row_ctr
= 0;
267 /* Simple case with no context needed */
268 main_ptr
->pub
.process_data
= process_data_simple_main
;
270 main_ptr
->buffer_full
= FALSE
; /* Mark buffer empty */
271 main_ptr
->rowgroup_ctr
= 0;
273 #ifdef QUANT_2PASS_SUPPORTED
274 case JBUF_CRANK_DEST
:
275 /* For last pass of 2-pass quantization, just crank the postprocessor */
276 main_ptr
->pub
.process_data
= process_data_crank_post
;
280 ERREXIT(cinfo
, JERR_BAD_BUFFER_MODE
);
288 * This handles the simple case where no context is required.
292 process_data_simple_main(j_decompress_ptr cinfo
, JSAMPARRAY output_buf
,
293 JDIMENSION
*out_row_ctr
, JDIMENSION out_rows_avail
)
295 my_main_ptr main_ptr
= (my_main_ptr
)cinfo
->main
;
296 JDIMENSION rowgroups_avail
;
298 /* Read input data if we haven't filled the main buffer yet */
299 if (!main_ptr
->buffer_full
) {
300 if (!(*cinfo
->coef
->decompress_data
) (cinfo
, main_ptr
->buffer
))
301 return; /* suspension forced, can do nothing more */
302 main_ptr
->buffer_full
= TRUE
; /* OK, we have an iMCU row to work with */
305 /* There are always min_DCT_scaled_size row groups in an iMCU row. */
306 rowgroups_avail
= (JDIMENSION
)cinfo
->_min_DCT_scaled_size
;
307 /* Note: at the bottom of the image, we may pass extra garbage row groups
308 * to the postprocessor. The postprocessor has to check for bottom
309 * of image anyway (at row resolution), so no point in us doing it too.
312 /* Feed the postprocessor */
313 (*cinfo
->post
->post_process_data
) (cinfo
, main_ptr
->buffer
,
314 &main_ptr
->rowgroup_ctr
, rowgroups_avail
,
315 output_buf
, out_row_ctr
, out_rows_avail
);
317 /* Has postprocessor consumed all the data yet? If so, mark buffer empty */
318 if (main_ptr
->rowgroup_ctr
>= rowgroups_avail
) {
319 main_ptr
->buffer_full
= FALSE
;
320 main_ptr
->rowgroup_ctr
= 0;
327 * This handles the case where context rows must be provided.
331 process_data_context_main(j_decompress_ptr cinfo
, JSAMPARRAY output_buf
,
332 JDIMENSION
*out_row_ctr
, JDIMENSION out_rows_avail
)
334 my_main_ptr main_ptr
= (my_main_ptr
)cinfo
->main
;
336 /* Read input data if we haven't filled the main buffer yet */
337 if (!main_ptr
->buffer_full
) {
338 if (!(*cinfo
->coef
->decompress_data
) (cinfo
,
339 main_ptr
->xbuffer
[main_ptr
->whichptr
]))
340 return; /* suspension forced, can do nothing more */
341 main_ptr
->buffer_full
= TRUE
; /* OK, we have an iMCU row to work with */
342 main_ptr
->iMCU_row_ctr
++; /* count rows received */
345 /* Postprocessor typically will not swallow all the input data it is handed
346 * in one call (due to filling the output buffer first). Must be prepared
347 * to exit and restart. This switch lets us keep track of how far we got.
348 * Note that each case falls through to the next on successful completion.
350 switch (main_ptr
->context_state
) {
351 case CTX_POSTPONED_ROW
:
352 /* Call postprocessor using previously set pointers for postponed row */
353 (*cinfo
->post
->post_process_data
) (cinfo
,
354 main_ptr
->xbuffer
[main_ptr
->whichptr
],
355 &main_ptr
->rowgroup_ctr
,
356 main_ptr
->rowgroups_avail
, output_buf
,
357 out_row_ctr
, out_rows_avail
);
358 if (main_ptr
->rowgroup_ctr
< main_ptr
->rowgroups_avail
)
359 return; /* Need to suspend */
360 main_ptr
->context_state
= CTX_PREPARE_FOR_IMCU
;
361 if (*out_row_ctr
>= out_rows_avail
)
362 return; /* Postprocessor exactly filled output buf */
363 FALLTHROUGH
/*FALLTHROUGH*/
364 case CTX_PREPARE_FOR_IMCU
:
365 /* Prepare to process first M-1 row groups of this iMCU row */
366 main_ptr
->rowgroup_ctr
= 0;
367 main_ptr
->rowgroups_avail
= (JDIMENSION
)(cinfo
->_min_DCT_scaled_size
- 1);
368 /* Check for bottom of image: if so, tweak pointers to "duplicate"
369 * the last sample row, and adjust rowgroups_avail to ignore padding rows.
371 if (main_ptr
->iMCU_row_ctr
== cinfo
->total_iMCU_rows
)
372 set_bottom_pointers(cinfo
);
373 main_ptr
->context_state
= CTX_PROCESS_IMCU
;
374 FALLTHROUGH
/*FALLTHROUGH*/
375 case CTX_PROCESS_IMCU
:
376 /* Call postprocessor using previously set pointers */
377 (*cinfo
->post
->post_process_data
) (cinfo
,
378 main_ptr
->xbuffer
[main_ptr
->whichptr
],
379 &main_ptr
->rowgroup_ctr
,
380 main_ptr
->rowgroups_avail
, output_buf
,
381 out_row_ctr
, out_rows_avail
);
382 if (main_ptr
->rowgroup_ctr
< main_ptr
->rowgroups_avail
)
383 return; /* Need to suspend */
384 /* After the first iMCU, change wraparound pointers to normal state */
385 if (main_ptr
->iMCU_row_ctr
== 1)
386 set_wraparound_pointers(cinfo
);
387 /* Prepare to load new iMCU row using other xbuffer list */
388 main_ptr
->whichptr
^= 1; /* 0=>1 or 1=>0 */
389 main_ptr
->buffer_full
= FALSE
;
390 /* Still need to process last row group of this iMCU row, */
391 /* which is saved at index M+1 of the other xbuffer */
392 main_ptr
->rowgroup_ctr
= (JDIMENSION
)(cinfo
->_min_DCT_scaled_size
+ 1);
393 main_ptr
->rowgroups_avail
= (JDIMENSION
)(cinfo
->_min_DCT_scaled_size
+ 2);
394 main_ptr
->context_state
= CTX_POSTPONED_ROW
;
401 * Final pass of two-pass quantization: just call the postprocessor.
402 * Source data will be the postprocessor controller's internal buffer.
405 #ifdef QUANT_2PASS_SUPPORTED
408 process_data_crank_post(j_decompress_ptr cinfo
, JSAMPARRAY output_buf
,
409 JDIMENSION
*out_row_ctr
, JDIMENSION out_rows_avail
)
411 (*cinfo
->post
->post_process_data
) (cinfo
, (JSAMPIMAGE
)NULL
,
412 (JDIMENSION
*)NULL
, (JDIMENSION
)0,
413 output_buf
, out_row_ctr
, out_rows_avail
);
416 #endif /* QUANT_2PASS_SUPPORTED */
420 * Initialize main buffer controller.
424 jinit_d_main_controller(j_decompress_ptr cinfo
, boolean need_full_buffer
)
426 my_main_ptr main_ptr
;
427 int ci
, rgroup
, ngroups
;
428 jpeg_component_info
*compptr
;
430 main_ptr
= (my_main_ptr
)
431 (*cinfo
->mem
->alloc_small
) ((j_common_ptr
)cinfo
, JPOOL_IMAGE
,
432 sizeof(my_main_controller
));
433 cinfo
->main
= (struct jpeg_d_main_controller
*)main_ptr
;
434 main_ptr
->pub
.start_pass
= start_pass_main
;
436 if (need_full_buffer
) /* shouldn't happen */
437 ERREXIT(cinfo
, JERR_BAD_BUFFER_MODE
);
439 /* Allocate the workspace.
440 * ngroups is the number of row groups we need.
442 if (cinfo
->upsample
->need_context_rows
) {
443 if (cinfo
->_min_DCT_scaled_size
< 2) /* unsupported, see comments above */
444 ERREXIT(cinfo
, JERR_NOTIMPL
);
445 alloc_funny_pointers(cinfo
); /* Alloc space for xbuffer[] lists */
446 ngroups
= cinfo
->_min_DCT_scaled_size
+ 2;
448 ngroups
= cinfo
->_min_DCT_scaled_size
;
451 for (ci
= 0, compptr
= cinfo
->comp_info
; ci
< cinfo
->num_components
;
453 rgroup
= (compptr
->v_samp_factor
* compptr
->_DCT_scaled_size
) /
454 cinfo
->_min_DCT_scaled_size
; /* height of a row group of component */
455 main_ptr
->buffer
[ci
] = (*cinfo
->mem
->alloc_sarray
)
456 ((j_common_ptr
)cinfo
, JPOOL_IMAGE
,
457 compptr
->width_in_blocks
* compptr
->_DCT_scaled_size
,
458 (JDIMENSION
)(rgroup
* ngroups
));