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.
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.
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.
16
#define JPEG_INTERNALS
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.
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
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.
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.
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.
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
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* 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.)
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* 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.)
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* 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
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* of row groups per iMCU row). We create two sets of redundant pointers to
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* the workspace. Labeling the physical row groups 0 to M+1, the synthesized
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* pointer lists look like this:
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* master pointer --> 0 master pointer --> 0
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* We read alternate iMCU rows using each master pointer; thus the last two
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* 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
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* The above pictures describe the normal state of the pointer lists.
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* 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).
102
* This scheme breaks down if M < 2, ie, min_DCT_scaled_size is 1. In that
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* 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
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* 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.
112
/* Private buffer controller object */
115
struct jpeg_d_main_controller pub; /* public fields */
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/* Pointer to allocated workspace (M or M+2 row groups). */
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JSAMPARRAY buffer[MAX_COMPONENTS];
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boolean buffer_full; /* Have we gotten an iMCU row from decoder? */
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JDIMENSION rowgroup_ctr; /* counts row groups output to postprocessor */
123
/* Remaining fields are only used in the context case. */
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/* These are the master pointers to the funny-order pointer lists. */
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JSAMPIMAGE xbuffer[2]; /* pointers to weird pointer lists */
128
int whichptr; /* indicates which pointer set is now in use */
129
int context_state; /* process_data state machine status */
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JDIMENSION rowgroups_avail; /* row groups available to postprocessor */
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JDIMENSION iMCU_row_ctr; /* counts iMCU rows to detect image top/bot */
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} my_main_controller;
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typedef my_main_controller * my_main_ptr;
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/* context_state values: */
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#define CTX_PREPARE_FOR_IMCU 0 /* need to prepare for MCU row */
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#define CTX_PROCESS_IMCU 1 /* feeding iMCU to postprocessor */
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#define CTX_POSTPONED_ROW 2 /* feeding postponed row group */
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/* Forward declarations */
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METHODDEF(void) process_data_simple_main
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JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
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JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
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METHODDEF(void) process_data_context_main
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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));
157
alloc_funny_pointers (j_decompress_ptr cinfo)
158
/* Allocate space for the funny pointer lists.
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* This is done only once, not once per pass.
162
my_main_ptr jmain = (my_main_ptr) cinfo->main;
164
int M = cinfo->min_DCT_scaled_size;
165
jpeg_component_info *compptr;
168
/* Get top-level space for component array pointers.
169
* We alloc both arrays with one call to save a few cycles.
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jmain->xbuffer[0] = (JSAMPIMAGE)
172
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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cinfo->num_components * 2 * SIZEOF(JSAMPARRAY));
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jmain->xbuffer[1] = jmain->xbuffer[0] + cinfo->num_components;
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for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
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rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
179
cinfo->min_DCT_scaled_size; /* height of a row group of component */
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/* Get space for pointer lists --- M+4 row groups in each list.
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* We alloc both pointer lists with one call to save a few cycles.
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
185
2 * (rgroup * (M + 4)) * SIZEOF(JSAMPROW));
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xbuf += rgroup; /* want one row group at negative offsets */
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jmain->xbuffer[0][ci] = xbuf;
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xbuf += rgroup * (M + 4);
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jmain->xbuffer[1][ci] = xbuf;
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make_funny_pointers (j_decompress_ptr cinfo)
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/* Create the funny pointer lists discussed in the comments above.
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* The actual workspace is already allocated (in jmain->buffer),
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* 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.
203
my_main_ptr jmain = (my_main_ptr) cinfo->main;
205
int M = cinfo->min_DCT_scaled_size;
206
jpeg_component_info *compptr;
207
JSAMPARRAY buf, xbuf0, xbuf1;
209
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
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rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
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cinfo->min_DCT_scaled_size; /* height of a row group of component */
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xbuf0 = jmain->xbuffer[0][ci];
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xbuf1 = jmain->xbuffer[1][ci];
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/* First copy the workspace pointers as-is */
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buf = jmain->buffer[ci];
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for (i = 0; i < rgroup * (M + 2); i++) {
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xbuf0[i] = xbuf1[i] = buf[i];
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/* In the second list, put the last four row groups in swapped order */
221
for (i = 0; i < rgroup * 2; i++) {
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xbuf1[rgroup*(M-2) + i] = buf[rgroup*M + i];
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xbuf1[rgroup*M + i] = buf[rgroup*(M-2) + i];
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].
230
for (i = 0; i < rgroup; i++) {
231
xbuf0[i - rgroup] = xbuf0[0];
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.
243
my_main_ptr jmain = (my_main_ptr) cinfo->main;
245
int M = cinfo->min_DCT_scaled_size;
246
jpeg_component_info *compptr;
247
JSAMPARRAY xbuf0, xbuf1;
249
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
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rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
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cinfo->min_DCT_scaled_size; /* height of a row group of component */
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xbuf0 = jmain->xbuffer[0][ci];
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xbuf1 = jmain->xbuffer[1][ci];
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for (i = 0; i < rgroup; i++) {
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xbuf0[i - rgroup] = xbuf0[rgroup*(M+1) + i];
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xbuf1[i - rgroup] = xbuf1[rgroup*(M+1) + i];
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xbuf0[rgroup*(M+2) + i] = xbuf0[i];
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xbuf1[rgroup*(M+2) + i] = xbuf1[i];
266
set_bottom_pointers (j_decompress_ptr cinfo)
267
/* Change the pointer lists to duplicate the last sample row at the bottom
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* 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.
272
my_main_ptr jmain = (my_main_ptr) cinfo->main;
273
int ci, i, rgroup, iMCUheight, rows_left;
274
jpeg_component_info *compptr;
277
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
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.
289
jmain->rowgroups_avail = (JDIMENSION) ((rows_left-1) / rgroup + 1);
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.
294
xbuf = jmain->xbuffer[jmain->whichptr][ci];
295
for (i = 0; i < rgroup * 2; i++) {
296
xbuf[rows_left + i] = xbuf[rows_left-1];
303
* Initialize for a processing pass.
307
start_pass_main (j_decompress_ptr cinfo, J_BUF_MODE pass_mode)
309
my_main_ptr jmain = (my_main_ptr) cinfo->main;
313
if (cinfo->upsample->need_context_rows) {
314
jmain->pub.process_data = process_data_context_main;
315
make_funny_pointers(cinfo); /* Create the xbuffer[] lists */
316
jmain->whichptr = 0; /* Read first iMCU row into xbuffer[0] */
317
jmain->context_state = CTX_PREPARE_FOR_IMCU;
318
jmain->iMCU_row_ctr = 0;
320
/* Simple case with no context needed */
321
jmain->pub.process_data = process_data_simple_main;
323
jmain->buffer_full = FALSE; /* Mark buffer empty */
324
jmain->rowgroup_ctr = 0;
326
#ifdef QUANT_2PASS_SUPPORTED
327
case JBUF_CRANK_DEST:
328
/* For last pass of 2-pass quantization, just crank the postprocessor */
329
jmain->pub.process_data = process_data_crank_post;
333
ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
341
* This handles the simple case where no context is required.
345
process_data_simple_main (j_decompress_ptr cinfo,
346
JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
347
JDIMENSION out_rows_avail)
349
my_main_ptr jmain = (my_main_ptr) cinfo->main;
350
JDIMENSION rowgroups_avail;
352
/* Read input data if we haven't filled the main buffer yet */
353
if (! jmain->buffer_full) {
354
if (! (*cinfo->coef->decompress_data) (cinfo, jmain->buffer))
355
return; /* suspension forced, can do nothing more */
356
jmain->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
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.
366
/* Feed the postprocessor */
367
(*cinfo->post->post_process_data) (cinfo, jmain->buffer,
368
&jmain->rowgroup_ctr, rowgroups_avail,
369
output_buf, out_row_ctr, out_rows_avail);
371
/* Has postprocessor consumed all the data yet? If so, mark buffer empty */
372
if (jmain->rowgroup_ctr >= rowgroups_avail) {
373
jmain->buffer_full = FALSE;
374
jmain->rowgroup_ctr = 0;
381
* This handles the case where context rows must be provided.
385
process_data_context_main (j_decompress_ptr cinfo,
386
JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
387
JDIMENSION out_rows_avail)
389
my_main_ptr jmain = (my_main_ptr) cinfo->main;
391
/* Read input data if we haven't filled the main buffer yet */
392
if (! jmain->buffer_full) {
393
if (! (*cinfo->coef->decompress_data) (cinfo,
394
jmain->xbuffer[jmain->whichptr]))
395
return; /* suspension forced, can do nothing more */
396
jmain->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
397
jmain->iMCU_row_ctr++; /* count rows received */
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.
405
switch (jmain->context_state) {
406
case CTX_POSTPONED_ROW:
407
/* Call postprocessor using previously set pointers for postponed row */
408
(*cinfo->post->post_process_data) (cinfo, jmain->xbuffer[jmain->whichptr],
409
&jmain->rowgroup_ctr, jmain->rowgroups_avail,
410
output_buf, out_row_ctr, out_rows_avail);
411
if (jmain->rowgroup_ctr < jmain->rowgroups_avail)
412
return; /* Need to suspend */
413
jmain->context_state = CTX_PREPARE_FOR_IMCU;
414
if (*out_row_ctr >= out_rows_avail)
415
return; /* Postprocessor exactly filled output buf */
417
case CTX_PREPARE_FOR_IMCU:
418
/* Prepare to process first M-1 row groups of this iMCU row */
419
jmain->rowgroup_ctr = 0;
420
jmain->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.
424
if (jmain->iMCU_row_ctr == cinfo->total_iMCU_rows)
425
set_bottom_pointers(cinfo);
426
jmain->context_state = CTX_PROCESS_IMCU;
428
case CTX_PROCESS_IMCU:
429
/* Call postprocessor using previously set pointers */
430
(*cinfo->post->post_process_data) (cinfo, jmain->xbuffer[jmain->whichptr],
431
&jmain->rowgroup_ctr, jmain->rowgroups_avail,
432
output_buf, out_row_ctr, out_rows_avail);
433
if (jmain->rowgroup_ctr < jmain->rowgroups_avail)
434
return; /* Need to suspend */
435
/* After the first iMCU, change wraparound pointers to normal state */
436
if (jmain->iMCU_row_ctr == 1)
437
set_wraparound_pointers(cinfo);
438
/* Prepare to load new iMCU row using other xbuffer list */
439
jmain->whichptr ^= 1; /* 0=>1 or 1=>0 */
440
jmain->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
jmain->rowgroup_ctr = (JDIMENSION) (cinfo->min_DCT_scaled_size + 1);
444
jmain->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size + 2);
445
jmain->context_state = CTX_POSTPONED_ROW;
452
* Final pass of two-pass quantization: just call the postprocessor.
453
* Source data will be the postprocessor controller's internal buffer.
456
#ifdef QUANT_2PASS_SUPPORTED
459
process_data_crank_post (j_decompress_ptr cinfo,
460
JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
461
JDIMENSION out_rows_avail)
463
(*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE) NULL,
464
(JDIMENSION *) NULL, (JDIMENSION) 0,
465
output_buf, out_row_ctr, out_rows_avail);
468
#endif /* QUANT_2PASS_SUPPORTED */
472
* Initialize main buffer controller.
476
jinit_d_main_controller (j_decompress_ptr cinfo, boolean need_full_buffer)
479
int ci, rgroup, ngroups;
480
jpeg_component_info *compptr;
482
jmain = (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 *) jmain;
486
jmain->pub.start_pass = start_pass_main;
488
if (need_full_buffer) /* shouldn't happen */
489
ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
491
/* Allocate the workspace.
492
* ngroups is the number of row groups we need.
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;
500
ngroups = cinfo->min_DCT_scaled_size;
503
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
505
rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
506
cinfo->min_DCT_scaled_size; /* height of a row group of component */
507
jmain->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));
added
removed
jpeg/jdmainct.c
