1/*
2 * jcprepct.c
3 *
4 * This file is part of the Independent JPEG Group's software:
5 * Copyright (C) 1994-1996, Thomas G. Lane.
6 * It was modified by The libjpeg-turbo Project to include only code relevant
7 * to libjpeg-turbo.
8 * For conditions of distribution and use, see the accompanying README.ijg
9 * file.
10 *
11 * This file contains the compression preprocessing controller.
12 * This controller manages the color conversion, downsampling,
13 * and edge expansion steps.
14 *
15 * Most of the complexity here is associated with buffering input rows
16 * as required by the downsampler.  See the comments at the head of
17 * jcsample.c for the downsampler's needs.
18 */
19
20#define JPEG_INTERNALS
21#include "jinclude.h"
22#include "jpeglib.h"
23
24
25/* At present, jcsample.c can request context rows only for smoothing.
26 * In the future, we might also need context rows for CCIR601 sampling
27 * or other more-complex downsampling procedures.  The code to support
28 * context rows should be compiled only if needed.
29 */
30#ifdef INPUT_SMOOTHING_SUPPORTED
31#define CONTEXT_ROWS_SUPPORTED
32#endif
33
34
35/*
36 * For the simple (no-context-row) case, we just need to buffer one
37 * row group's worth of pixels for the downsampling step.  At the bottom of
38 * the image, we pad to a full row group by replicating the last pixel row.
39 * The downsampler's last output row is then replicated if needed to pad
40 * out to a full iMCU row.
41 *
42 * When providing context rows, we must buffer three row groups' worth of
43 * pixels.  Three row groups are physically allocated, but the row pointer
44 * arrays are made five row groups high, with the extra pointers above and
45 * below "wrapping around" to point to the last and first real row groups.
46 * This allows the downsampler to access the proper context rows.
47 * At the top and bottom of the image, we create dummy context rows by
48 * copying the first or last real pixel row.  This copying could be avoided
49 * by pointer hacking as is done in jdmainct.c, but it doesn't seem worth the
50 * trouble on the compression side.
51 */
52
53
54/* Private buffer controller object */
55
56typedef struct {
57  struct jpeg_c_prep_controller pub; /* public fields */
58
59  /* Downsampling input buffer.  This buffer holds color-converted data
60   * until we have enough to do a downsample step.
61   */
62  JSAMPARRAY color_buf[MAX_COMPONENTS];
63
64  JDIMENSION rows_to_go;        /* counts rows remaining in source image */
65  int next_buf_row;             /* index of next row to store in color_buf */
66
67#ifdef CONTEXT_ROWS_SUPPORTED   /* only needed for context case */
68  int this_row_group;           /* starting row index of group to process */
69  int next_buf_stop;            /* downsample when we reach this index */
70#endif
71} my_prep_controller;
72
73typedef my_prep_controller *my_prep_ptr;
74
75
76/*
77 * Initialize for a processing pass.
78 */
79
80METHODDEF(void)
81start_pass_prep (j_compress_ptr cinfo, J_BUF_MODE pass_mode)
82{
83  my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
84
85  if (pass_mode != JBUF_PASS_THRU)
86    ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
87
88  /* Initialize total-height counter for detecting bottom of image */
89  prep->rows_to_go = cinfo->image_height;
90  /* Mark the conversion buffer empty */
91  prep->next_buf_row = 0;
92#ifdef CONTEXT_ROWS_SUPPORTED
93  /* Preset additional state variables for context mode.
94   * These aren't used in non-context mode, so we needn't test which mode.
95   */
96  prep->this_row_group = 0;
97  /* Set next_buf_stop to stop after two row groups have been read in. */
98  prep->next_buf_stop = 2 * cinfo->max_v_samp_factor;
99#endif
100}
101
102
103/*
104 * Expand an image vertically from height input_rows to height output_rows,
105 * by duplicating the bottom row.
106 */
107
108LOCAL(void)
109expand_bottom_edge (JSAMPARRAY image_data, JDIMENSION num_cols,
110                    int input_rows, int output_rows)
111{
112  register int row;
113
114  for (row = input_rows; row < output_rows; row++) {
115    jcopy_sample_rows(image_data, input_rows-1, image_data, row,
116                      1, num_cols);
117  }
118}
119
120
121/*
122 * Process some data in the simple no-context case.
123 *
124 * Preprocessor output data is counted in "row groups".  A row group
125 * is defined to be v_samp_factor sample rows of each component.
126 * Downsampling will produce this much data from each max_v_samp_factor
127 * input rows.
128 */
129
130METHODDEF(void)
131pre_process_data (j_compress_ptr cinfo,
132                  JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
133                  JDIMENSION in_rows_avail,
134                  JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
135                  JDIMENSION out_row_groups_avail)
136{
137  my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
138  int numrows, ci;
139  JDIMENSION inrows;
140  jpeg_component_info *compptr;
141
142  while (*in_row_ctr < in_rows_avail &&
143         *out_row_group_ctr < out_row_groups_avail) {
144    /* Do color conversion to fill the conversion buffer. */
145    inrows = in_rows_avail - *in_row_ctr;
146    numrows = cinfo->max_v_samp_factor - prep->next_buf_row;
147    numrows = (int) MIN((JDIMENSION) numrows, inrows);
148    (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
149                                       prep->color_buf,
150                                       (JDIMENSION) prep->next_buf_row,
151                                       numrows);
152    *in_row_ctr += numrows;
153    prep->next_buf_row += numrows;
154    prep->rows_to_go -= numrows;
155    /* If at bottom of image, pad to fill the conversion buffer. */
156    if (prep->rows_to_go == 0 &&
157        prep->next_buf_row < cinfo->max_v_samp_factor) {
158      for (ci = 0; ci < cinfo->num_components; ci++) {
159        expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
160                           prep->next_buf_row, cinfo->max_v_samp_factor);
161      }
162      prep->next_buf_row = cinfo->max_v_samp_factor;
163    }
164    /* If we've filled the conversion buffer, empty it. */
165    if (prep->next_buf_row == cinfo->max_v_samp_factor) {
166      (*cinfo->downsample->downsample) (cinfo,
167                                        prep->color_buf, (JDIMENSION) 0,
168                                        output_buf, *out_row_group_ctr);
169      prep->next_buf_row = 0;
170      (*out_row_group_ctr)++;
171    }
172    /* If at bottom of image, pad the output to a full iMCU height.
173     * Note we assume the caller is providing a one-iMCU-height output buffer!
174     */
175    if (prep->rows_to_go == 0 &&
176        *out_row_group_ctr < out_row_groups_avail) {
177      for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
178           ci++, compptr++) {
179        expand_bottom_edge(output_buf[ci],
180                           compptr->width_in_blocks * DCTSIZE,
181                           (int) (*out_row_group_ctr * compptr->v_samp_factor),
182                           (int) (out_row_groups_avail * compptr->v_samp_factor));
183      }
184      *out_row_group_ctr = out_row_groups_avail;
185      break;                    /* can exit outer loop without test */
186    }
187  }
188}
189
190
191#ifdef CONTEXT_ROWS_SUPPORTED
192
193/*
194 * Process some data in the context case.
195 */
196
197METHODDEF(void)
198pre_process_context (j_compress_ptr cinfo,
199                     JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
200                     JDIMENSION in_rows_avail,
201                     JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
202                     JDIMENSION out_row_groups_avail)
203{
204  my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
205  int numrows, ci;
206  int buf_height = cinfo->max_v_samp_factor * 3;
207  JDIMENSION inrows;
208
209  while (*out_row_group_ctr < out_row_groups_avail) {
210    if (*in_row_ctr < in_rows_avail) {
211      /* Do color conversion to fill the conversion buffer. */
212      inrows = in_rows_avail - *in_row_ctr;
213      numrows = prep->next_buf_stop - prep->next_buf_row;
214      numrows = (int) MIN((JDIMENSION) numrows, inrows);
215      (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
216                                         prep->color_buf,
217                                         (JDIMENSION) prep->next_buf_row,
218                                         numrows);
219      /* Pad at top of image, if first time through */
220      if (prep->rows_to_go == cinfo->image_height) {
221        for (ci = 0; ci < cinfo->num_components; ci++) {
222          int row;
223          for (row = 1; row <= cinfo->max_v_samp_factor; row++) {
224            jcopy_sample_rows(prep->color_buf[ci], 0,
225                              prep->color_buf[ci], -row,
226                              1, cinfo->image_width);
227          }
228        }
229      }
230      *in_row_ctr += numrows;
231      prep->next_buf_row += numrows;
232      prep->rows_to_go -= numrows;
233    } else {
234      /* Return for more data, unless we are at the bottom of the image. */
235      if (prep->rows_to_go != 0)
236        break;
237      /* When at bottom of image, pad to fill the conversion buffer. */
238      if (prep->next_buf_row < prep->next_buf_stop) {
239        for (ci = 0; ci < cinfo->num_components; ci++) {
240          expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
241                             prep->next_buf_row, prep->next_buf_stop);
242        }
243        prep->next_buf_row = prep->next_buf_stop;
244      }
245    }
246    /* If we've gotten enough data, downsample a row group. */
247    if (prep->next_buf_row == prep->next_buf_stop) {
248      (*cinfo->downsample->downsample) (cinfo,
249                                        prep->color_buf,
250                                        (JDIMENSION) prep->this_row_group,
251                                        output_buf, *out_row_group_ctr);
252      (*out_row_group_ctr)++;
253      /* Advance pointers with wraparound as necessary. */
254      prep->this_row_group += cinfo->max_v_samp_factor;
255      if (prep->this_row_group >= buf_height)
256        prep->this_row_group = 0;
257      if (prep->next_buf_row >= buf_height)
258        prep->next_buf_row = 0;
259      prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor;
260    }
261  }
262}
263
264
265/*
266 * Create the wrapped-around downsampling input buffer needed for context mode.
267 */
268
269LOCAL(void)
270create_context_buffer (j_compress_ptr cinfo)
271{
272  my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
273  int rgroup_height = cinfo->max_v_samp_factor;
274  int ci, i;
275  jpeg_component_info *compptr;
276  JSAMPARRAY true_buffer, fake_buffer;
277
278  /* Grab enough space for fake row pointers for all the components;
279   * we need five row groups' worth of pointers for each component.
280   */
281  fake_buffer = (JSAMPARRAY)
282    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
283                                (cinfo->num_components * 5 * rgroup_height) *
284                                sizeof(JSAMPROW));
285
286  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
287       ci++, compptr++) {
288    /* Allocate the actual buffer space (3 row groups) for this component.
289     * We make the buffer wide enough to allow the downsampler to edge-expand
290     * horizontally within the buffer, if it so chooses.
291     */
292    true_buffer = (*cinfo->mem->alloc_sarray)
293      ((j_common_ptr) cinfo, JPOOL_IMAGE,
294       (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
295                      cinfo->max_h_samp_factor) / compptr->h_samp_factor),
296       (JDIMENSION) (3 * rgroup_height));
297    /* Copy true buffer row pointers into the middle of the fake row array */
298    MEMCOPY(fake_buffer + rgroup_height, true_buffer,
299            3 * rgroup_height * sizeof(JSAMPROW));
300    /* Fill in the above and below wraparound pointers */
301    for (i = 0; i < rgroup_height; i++) {
302      fake_buffer[i] = true_buffer[2 * rgroup_height + i];
303      fake_buffer[4 * rgroup_height + i] = true_buffer[i];
304    }
305    prep->color_buf[ci] = fake_buffer + rgroup_height;
306    fake_buffer += 5 * rgroup_height; /* point to space for next component */
307  }
308}
309
310#endif /* CONTEXT_ROWS_SUPPORTED */
311
312
313/*
314 * Initialize preprocessing controller.
315 */
316
317GLOBAL(void)
318jinit_c_prep_controller (j_compress_ptr cinfo, boolean need_full_buffer)
319{
320  my_prep_ptr prep;
321  int ci;
322  jpeg_component_info *compptr;
323
324  if (need_full_buffer)         /* safety check */
325    ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
326
327  prep = (my_prep_ptr)
328    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
329                                sizeof(my_prep_controller));
330  cinfo->prep = (struct jpeg_c_prep_controller *) prep;
331  prep->pub.start_pass = start_pass_prep;
332
333  /* Allocate the color conversion buffer.
334   * We make the buffer wide enough to allow the downsampler to edge-expand
335   * horizontally within the buffer, if it so chooses.
336   */
337  if (cinfo->downsample->need_context_rows) {
338    /* Set up to provide context rows */
339#ifdef CONTEXT_ROWS_SUPPORTED
340    prep->pub.pre_process_data = pre_process_context;
341    create_context_buffer(cinfo);
342#else
343    ERREXIT(cinfo, JERR_NOT_COMPILED);
344#endif
345  } else {
346    /* No context, just make it tall enough for one row group */
347    prep->pub.pre_process_data = pre_process_data;
348    for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
349         ci++, compptr++) {
350      prep->color_buf[ci] = (*cinfo->mem->alloc_sarray)
351        ((j_common_ptr) cinfo, JPOOL_IMAGE,
352         (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
353                        cinfo->max_h_samp_factor) / compptr->h_samp_factor),
354         (JDIMENSION) cinfo->max_v_samp_factor);
355    }
356  }
357}
358