1 /****************************************************************************
2 * Copyright 2020,2023 Thomas E. Dickey *
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28 ****************************************************************************/
29
30 /****************************************************************************
31 * Author: Zeyd M. Ben-Halim <zmbenhal@netcom.com> 1992,1995 *
32 * and: Eric S. Raymond <esr@snark.thyrsus.com> *
33 * and: Thomas E. Dickey 1996-on *
34 * and: Alexander V Lukyanov 1997-1998 *
35 ****************************************************************************/
36
37 /******************************************************************************
38
39 NAME
40 hardscroll.c -- hardware-scrolling optimization for ncurses
41
42 SYNOPSIS
43 void _nc_scroll_optimize(void)
44
45 DESCRIPTION
46 OVERVIEW
47
48 This algorithm for computes optimum hardware scrolling to transform an
49 old screen (curscr) into a new screen (newscr) via vertical line moves.
50
51 Because the screen has a `grain' (there are insert/delete/scroll line
52 operations but no insert/delete/scroll column operations), it is efficient
53 break the update algorithm into two pieces: a first stage that does only line
54 moves, optimizing the end product of user-invoked insertions, deletions, and
55 scrolls; and a second phase (corresponding to the present doupdate code in
56 ncurses) that does only line transformations.
57
58 The common case we want hardware scrolling for is to handle line insertions
59 and deletions in screen-oriented text-editors. This two-stage approach will
60 accomplish that at a low computation and code-size cost.
61
62 LINE-MOVE COMPUTATION
63
64 Now, to a discussion of the line-move computation.
65
66 For expository purposes, consider the screen lines to be represented by
67 integers 0..23 (with the understanding that the value of 23 may vary).
68 Let a new line introduced by insertion, scrolling, or at the bottom of
69 the screen following a line delete be given the index -1.
70
71 Assume that the real screen starts with lines 0..23. Now, we have
72 the following possible line-oriented operations on the screen:
73
74 Insertion: inserts a line at a given screen row, forcing all lines below
75 to scroll forward. The last screen line is lost. For example, an insertion
76 at line 5 would produce: 0..4 -1 5..23.
77
78 Deletion: deletes a line at a given screen row, forcing all lines below
79 to scroll forward. The last screen line is made new. For example, a deletion
80 at line 7 would produce: 0..6 8..23 -1.
81
82 Scroll up: move a range of lines up 1. The bottom line of the range
83 becomes new. For example, scrolling up the region from 9 to 14 will
84 produce 0..8 10..14 -1 15..23.
85
86 Scroll down: move a range of lines down 1. The top line of the range
87 becomes new. For example, scrolling down the region from 12 to 16 will produce
88 0..11 -1 12..15 17..23.
89
90 Now, an obvious property of all these operations is that they preserve the
91 order of old lines, though not their position in the sequence.
92
93 The key trick of this algorithm is that the original line indices described
94 above are actually maintained as _line[].oldindex fields in the window
95 structure, and stick to each line through scroll and insert/delete operations.
96
97 Thus, it is possible at update time to look at the oldnum fields and compute
98 an optimal set of il/dl/scroll operations that will take the real screen
99 lines to the virtual screen lines. Once these vertical moves have been done,
100 we can hand off to the second stage of the update algorithm, which does line
101 transformations.
102
103 Note that the move computation does not need to have the full generality
104 of a diff algorithm (which it superficially resembles) because lines cannot
105 be moved out of order.
106
107 THE ALGORITHM
108
109 The scrolling is done in two passes. The first pass is from top to bottom
110 scroling hunks UP. The second one is from bottom to top scrolling hunks DOWN.
111 Obviously enough, no lines to be scrolled will be destroyed. (lav)
112
113 HOW TO TEST THIS:
114
115 Use the following production:
116
117 hardscroll: hardscroll.c
118 $(CC) -g -DSCROLLDEBUG hardscroll.c -o hardscroll
119
120 Then just type scramble vectors and watch. The following test loads are
121 a representative sample of cases:
122
123 ----------------------------- CUT HERE ------------------------------------
124 # No lines moved
125 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
126 #
127 # A scroll up
128 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 -1
129 #
130 # A scroll down
131 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
132 #
133 # An insertion (after line 12)
134 0 1 2 3 4 5 6 7 8 9 10 11 12 -1 13 14 15 16 17 18 19 20 21 22
135 #
136 # A simple deletion (line 10)
137 0 1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19 20 21 22 23 -1
138 #
139 # A more complex case
140 -1 -1 -1 -1 -1 3 4 5 6 7 -1 -1 8 9 10 11 12 13 14 15 16 17 -1 -1
141 ----------------------------- CUT HERE ------------------------------------
142
143 AUTHOR
144 Eric S. Raymond <esr@snark.thyrsus.com>, November 1994
145 New algorithm by Alexander V. Lukyanov <lav@yars.free.net>, Aug 1997
146
147 *****************************************************************************/
148
149 #include <curses.priv.h>
150
151 MODULE_ID("$Id: hardscroll.c,v 1.58 2023/09/09 16:04:08 Nicholas.Marriott Exp $")
152
153 #if defined(SCROLLDEBUG) || defined(HASHDEBUG)
154
155 # undef screen_lines
156 # define screen_lines(sp) MAXLINES
157 NCURSES_EXPORT_VAR (int)
158 oldnums[MAXLINES];
159 # define OLDNUM(sp,n) oldnums[n]
160 # define _tracef printf
161 # undef TR
162 # define TR(n, a) if (_nc_tracing & (n)) { _tracef a ; putchar('\n'); }
163
164 extern NCURSES_EXPORT_VAR(unsigned) _nc_tracing;
165
166 #else /* no debug */
167
168 /* OLDNUM(n) indicates which line will be shifted to the position n.
169 if OLDNUM(n) == _NEWINDEX, then the line n in new, not shifted from
170 somewhere. */
171 NCURSES_EXPORT_VAR (int *)
172 _nc_oldnums = 0; /* obsolete: keep for ABI compat */
173
174 # if USE_HASHMAP
175 # define oldnums(sp) (sp)->_oldnum_list
176 # define OLDNUM(sp,n) oldnums(sp)[n]
177 # else /* !USE_HASHMAP */
178 # define OLDNUM(sp,n) NewScreen(sp)->_line[n].oldindex
179 # endif /* !USE_HASHMAP */
180
181 #define OLDNUM_SIZE(sp) (sp)->_oldnum_size
182
183 #endif /* defined(SCROLLDEBUG) || defined(HASHDEBUG) */
184
185 NCURSES_EXPORT(void)
NCURSES_SP_NAME(_nc_scroll_optimize)186 NCURSES_SP_NAME(_nc_scroll_optimize) (NCURSES_SP_DCL0)
187 /* scroll optimization to transform curscr to newscr */
188 {
189 int i;
190 int start, end, shift;
191
192 TR(TRACE_ICALLS, (T_CALLED("_nc_scroll_optimize(%p)"), (void *) SP_PARM));
193
194 #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
195 #if USE_HASHMAP
196 /* get enough storage */
197 assert(OLDNUM_SIZE(SP_PARM) >= 0);
198 assert(screen_lines(SP_PARM) > 0);
199 if ((oldnums(SP_PARM) == 0)
200 || (OLDNUM_SIZE(SP_PARM) < screen_lines(SP_PARM))) {
201 int need_lines = ((OLDNUM_SIZE(SP_PARM) < screen_lines(SP_PARM))
202 ? screen_lines(SP_PARM)
203 : OLDNUM_SIZE(SP_PARM));
204 int *new_oldnums = typeRealloc(int,
205 (size_t) need_lines,
206 oldnums(SP_PARM));
207 if (!new_oldnums) {
208 TR(TRACE_ICALLS, (T_RETURN("")));
209 return;
210 }
211 oldnums(SP_PARM) = new_oldnums;
212 OLDNUM_SIZE(SP_PARM) = need_lines;
213 }
214 /* calculate the indices */
215 NCURSES_SP_NAME(_nc_hash_map) (NCURSES_SP_ARG);
216 if (SP_PARM->hashtab_len < screen_lines(SP_PARM)) {
217 TR(TRACE_ICALLS, (T_RETURN("")));
218 return;
219 }
220 #endif
221 #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
222
223 #ifdef TRACE
224 if (USE_TRACEF(TRACE_UPDATE | TRACE_MOVE)) {
225 NCURSES_SP_NAME(_nc_linedump) (NCURSES_SP_ARG);
226 _nc_unlock_global(tracef);
227 }
228 #endif /* TRACE */
229
230 /* pass 1 - from top to bottom scrolling up */
231 for (i = 0; i < screen_lines(SP_PARM);) {
232 while (i < screen_lines(SP_PARM)
233 && (OLDNUM(SP_PARM, i) == _NEWINDEX || OLDNUM(SP_PARM, i) <= i))
234 i++;
235 if (i >= screen_lines(SP_PARM))
236 break;
237
238 shift = OLDNUM(SP_PARM, i) - i; /* shift > 0 */
239 start = i;
240
241 i++;
242 while (i < screen_lines(SP_PARM)
243 && OLDNUM(SP_PARM, i) != _NEWINDEX
244 && OLDNUM(SP_PARM, i) - i == shift)
245 i++;
246 end = i - 1 + shift;
247
248 TR(TRACE_UPDATE | TRACE_MOVE, ("scroll [%d, %d] by %d", start, end, shift));
249 #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
250 if (NCURSES_SP_NAME(_nc_scrolln) (NCURSES_SP_ARGx
251 shift,
252 start,
253 end,
254 screen_lines(SP_PARM) - 1) == ERR) {
255 TR(TRACE_UPDATE | TRACE_MOVE, ("unable to scroll"));
256 continue;
257 }
258 #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
259 }
260
261 /* pass 2 - from bottom to top scrolling down */
262 for (i = screen_lines(SP_PARM) - 1; i >= 0;) {
263 while (i >= 0
264 && (OLDNUM(SP_PARM, i) == _NEWINDEX
265 || OLDNUM(SP_PARM, i) >= i)) {
266 i--;
267 }
268 if (i < 0)
269 break;
270
271 shift = OLDNUM(SP_PARM, i) - i; /* shift < 0 */
272 end = i;
273
274 i--;
275 while (i >= 0
276 && OLDNUM(SP_PARM, i) != _NEWINDEX
277 && OLDNUM(SP_PARM, i) - i == shift) {
278 i--;
279 }
280 start = i + 1 - (-shift);
281
282 TR(TRACE_UPDATE | TRACE_MOVE, ("scroll [%d, %d] by %d", start, end, shift));
283 #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
284 if (NCURSES_SP_NAME(_nc_scrolln) (NCURSES_SP_ARGx
285 shift,
286 start,
287 end,
288 screen_lines(SP_PARM) - 1) == ERR) {
289 TR(TRACE_UPDATE | TRACE_MOVE, ("unable to scroll"));
290 continue;
291 }
292 #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
293 }
294 TR(TRACE_ICALLS, (T_RETURN("")));
295 }
296
297 #if NCURSES_SP_FUNCS
298 NCURSES_EXPORT(void)
_nc_scroll_optimize(void)299 _nc_scroll_optimize(void)
300 {
301 NCURSES_SP_NAME(_nc_scroll_optimize) (CURRENT_SCREEN);
302 }
303 #endif
304
305 #if defined(TRACE) || defined(SCROLLDEBUG) || defined(HASHDEBUG)
306 NCURSES_EXPORT(void)
NCURSES_SP_NAME(_nc_linedump)307 NCURSES_SP_NAME(_nc_linedump) (NCURSES_SP_DCL0)
308 /* dump the state of the real and virtual oldnum fields */
309 {
310 if (USE_TRACEF(TRACE_UPDATE | TRACE_MOVE)) {
311 char *buf = 0;
312 size_t want = ((size_t) screen_lines(SP_PARM) + 1) * 4;
313 (void) SP_PARM;
314
315 if ((buf = typeMalloc(char, want)) != 0) {
316 int n;
317
318 *buf = '\0';
319 for (n = 0; n < screen_lines(SP_PARM); n++) {
320 int number = OLDNUM(SP_PARM, n);
321 if (number >= -99 && number < 999) {
322 _nc_SPRINTF(buf + strlen(buf),
323 _nc_SLIMIT(want - strlen(buf))
324 " %02d", number);
325 } else {
326 _nc_STRCAT(buf, " ??", want - strlen(buf));
327 }
328 }
329 free(buf);
330 }
331 }
332 }
333
334 #if NCURSES_SP_FUNCS
335 NCURSES_EXPORT(void)
_nc_linedump(void)336 _nc_linedump(void)
337 {
338 NCURSES_SP_NAME(_nc_linedump) (CURRENT_SCREEN);
339 }
340 #endif
341
342 #endif /* defined(TRACE) || defined(SCROLLDEBUG) */
343
344 #ifdef SCROLLDEBUG
345
346 int
main(int argc GCC_UNUSED,char * argv[]GCC_UNUSED)347 main(int argc GCC_UNUSED, char *argv[]GCC_UNUSED)
348 {
349 char line[BUFSIZ], *st;
350
351 #ifdef TRACE
352 _nc_tracing = TRACE_MOVE;
353 #endif
354 for (;;) {
355 int n;
356
357 for (n = 0; n < screen_lines(sp); n++)
358 oldnums[n] = _NEWINDEX;
359
360 /* grab the test vector */
361 if (fgets(line, sizeof(line), stdin) == (char *) NULL)
362 exit(EXIT_SUCCESS);
363
364 /* parse it */
365 n = 0;
366 if (line[0] == '#') {
367 (void) fputs(line, stderr);
368 continue;
369 }
370 st = strtok(line, " ");
371 do {
372 oldnums[n++] = atoi(st);
373 } while
374 ((st = strtok((char *) NULL, " ")) != 0);
375
376 /* display it */
377 (void) fputs("Initial input:\n", stderr);
378 _nc_linedump();
379
380 _nc_scroll_optimize();
381 }
382 }
383
384 #endif /* SCROLLDEBUG */
385
386 /* hardscroll.c ends here */
387