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28
29 /****************************************************************************
30 * Author: Zeyd M. Ben-Halim <zmbenhal@netcom.com> 1992,1995 *
31 * and: Eric S. Raymond <esr@snark.thyrsus.com> *
32 ****************************************************************************/
33
34 /******************************************************************************
35
36 NAME
37 hardscroll.c -- hardware-scrolling optimization for ncurses
38
39 SYNOPSIS
40 void _nc_scroll_optimize(void)
41
42 DESCRIPTION
43 OVERVIEW
44
45 This algorithm for computes optimum hardware scrolling to transform an
46 old screen (curscr) into a new screen (newscr) via vertical line moves.
47
48 Because the screen has a `grain' (there are insert/delete/scroll line
49 operations but no insert/delete/scroll column operations), it is efficient
50 break the update algorithm into two pieces: a first stage that does only line
51 moves, optimizing the end product of user-invoked insertions, deletions, and
52 scrolls; and a second phase (corresponding to the present doupdate code in
53 ncurses) that does only line transformations.
54
55 The common case we want hardware scrolling for is to handle line insertions
56 and deletions in screen-oriented text-editors. This two-stage approach will
57 accomplish that at a low computation and code-size cost.
58
59 LINE-MOVE COMPUTATION
60
61 Now, to a discussion of the line-move computation.
62
63 For expository purposes, consider the screen lines to be represented by
64 integers 0..23 (with the understanding that the value of 23 may vary).
65 Let a new line introduced by insertion, scrolling, or at the bottom of
66 the screen following a line delete be given the index -1.
67
68 Assume that the real screen starts with lines 0..23. Now, we have
69 the following possible line-oriented operations on the screen:
70
71 Insertion: inserts a line at a given screen row, forcing all lines below
72 to scroll forward. The last screen line is lost. For example, an insertion
73 at line 5 would produce: 0..4 -1 5..23.
74
75 Deletion: deletes a line at a given screen row, forcing all lines below
76 to scroll forward. The last screen line is made new. For example, a deletion
77 at line 7 would produce: 0..6 8..23 -1.
78
79 Scroll up: move a range of lines up 1. The bottom line of the range
80 becomes new. For example, scrolling up the region from 9 to 14 will
81 produce 0..8 10..14 -1 15..23.
82
83 Scroll down: move a range of lines down 1. The top line of the range
84 becomes new. For example, scrolling down the region from 12 to 16 will produce
85 0..11 -1 12..15 17..23.
86
87 Now, an obvious property of all these operations is that they preserve the
88 order of old lines, though not their position in the sequence.
89
90 The key trick of this algorithm is that the original line indices described
91 above are actually maintained as _line[].oldindex fields in the window
92 structure, and stick to each line through scroll and insert/delete operations.
93
94 Thus, it is possible at update time to look at the oldnum fields and compute
95 an optimal set of il/dl/scroll operations that will take the real screen
96 lines to the virtual screen lines. Once these vertical moves have been done,
97 we can hand off to the second stage of the update algorithm, which does line
98 transformations.
99
100 Note that the move computation does not need to have the full generality
101 of a diff algorithm (which it superficially resembles) because lines cannot
102 be moved out of order.
103
104 THE ALGORITHM
105
106 The scrolling is done in two passes. The first pass is from top to bottom
107 scroling hunks UP. The second one is from bottom to top scrolling hunks DOWN.
108 Obviously enough, no lines to be scrolled will be destroyed. (lav)
109
110 HOW TO TEST THIS:
111
112 Use the following production:
113
114 hardscroll: hardscroll.c
115 $(CC) -g -DSCROLLDEBUG hardscroll.c -o hardscroll
116
117 Then just type scramble vectors and watch. The following test loads are
118 a representative sample of cases:
119
120 ----------------------------- CUT HERE ------------------------------------
121 # No lines moved
122 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
123 #
124 # A scroll up
125 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 -1
126 #
127 # A scroll down
128 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
129 #
130 # An insertion (after line 12)
131 0 1 2 3 4 5 6 7 8 9 10 11 12 -1 13 14 15 16 17 18 19 20 21 22
132 #
133 # A simple deletion (line 10)
134 0 1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19 20 21 22 23 -1
135 #
136 # A more complex case
137 -1 -1 -1 -1 -1 3 4 5 6 7 -1 -1 8 9 10 11 12 13 14 15 16 17 -1 -1
138 ----------------------------- CUT HERE ------------------------------------
139
140 AUTHOR
141 Eric S. Raymond <esr@snark.thyrsus.com>, November 1994
142 New algorithm by Alexander V. Lukyanov <lav@yars.free.net>, Aug 1997
143
144 *****************************************************************************/
145
146 #include <curses.priv.h>
147
148 MODULE_ID("$Id: hardscroll.c,v 1.36 2001/01/14 00:17:28 tom Exp $")
149
150 #if defined(SCROLLDEBUG) || defined(HASHDEBUG)
151
152 # undef screen_lines
153 # define screen_lines MAXLINES
154 NCURSES_EXPORT_VAR(int)
155 oldnums[MAXLINES];
156 # define OLDNUM(n) oldnums[n]
157 # define _tracef printf
158 # undef TR
159 # define TR(n, a) if (_nc_tracing & (n)) { _tracef a ; putchar('\n'); }
160
161 #else /* no debug */
162
163 /* OLDNUM(n) indicates which line will be shifted to the position n.
164 if OLDNUM(n) == _NEWINDEX, then the line n in new, not shifted from
165 somewhere. */
166 NCURSES_EXPORT_VAR(int *)
167 _nc_oldnums = 0;
168
169 # if USE_HASHMAP
170 static int oldnums_allocated = 0;
171 # define oldnums _nc_oldnums
172 # define OLDNUM(n) oldnums[n]
173 # else /* !USE_HASHMAP */
174 # define OLDNUM(n) newscr->_line[n].oldindex
175 # endif /* !USE_HASHMAP */
176
177 #endif /* defined(SCROLLDEBUG) || defined(HASHDEBUG) */
178
179 NCURSES_EXPORT(void)
_nc_scroll_optimize(void)180 _nc_scroll_optimize(void)
181 /* scroll optimization to transform curscr to newscr */
182 {
183 int i;
184 int start, end, shift;
185
186 TR(TRACE_ICALLS, ("_nc_scroll_optimize() begins"));
187
188 #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
189 #if USE_HASHMAP
190 /* get enough storage */
191 if (oldnums_allocated < screen_lines) {
192 int *new_oldnums = typeRealloc(int, screen_lines, oldnums);
193 if (!new_oldnums)
194 return;
195 oldnums = new_oldnums;
196 oldnums_allocated = screen_lines;
197 }
198 /* calculate the indices */
199 _nc_hash_map();
200 #endif
201 #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
202
203 #ifdef TRACE
204 if (_nc_tracing & (TRACE_UPDATE | TRACE_MOVE))
205 _nc_linedump();
206 #endif /* TRACE */
207
208 /* pass 1 - from top to bottom scrolling up */
209 for (i = 0; i < screen_lines;) {
210 while (i < screen_lines && (OLDNUM(i) == _NEWINDEX || OLDNUM(i) <= i))
211 i++;
212 if (i >= screen_lines)
213 break;
214
215 shift = OLDNUM(i) - i; /* shift > 0 */
216 start = i;
217
218 i++;
219 while (i < screen_lines && OLDNUM(i) != _NEWINDEX && OLDNUM(i) - i
220 == shift)
221 i++;
222 end = i - 1 + shift;
223
224 TR(TRACE_UPDATE | TRACE_MOVE, ("scroll [%d, %d] by %d", start, end, shift));
225 #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
226 if (_nc_scrolln(shift, start, end, screen_lines - 1) == ERR) {
227 TR(TRACE_UPDATE | TRACE_MOVE, ("unable to scroll"));
228 continue;
229 }
230 #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
231 }
232
233 /* pass 2 - from bottom to top scrolling down */
234 for (i = screen_lines - 1; i >= 0;) {
235 while (i >= 0 && (OLDNUM(i) == _NEWINDEX || OLDNUM(i) >= i))
236 i--;
237 if (i < 0)
238 break;
239
240 shift = OLDNUM(i) - i; /* shift < 0 */
241 end = i;
242
243 i--;
244 while (i >= 0 && OLDNUM(i) != _NEWINDEX && OLDNUM(i) - i == shift)
245 i--;
246 start = 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 (_nc_scrolln(shift, start, end, screen_lines - 1) == ERR) {
251 TR(TRACE_UPDATE | TRACE_MOVE, ("unable to scroll"));
252 continue;
253 }
254 #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
255 }
256 }
257
258 #if defined(TRACE) || defined(SCROLLDEBUG) || defined(HASHDEBUG)
259 NCURSES_EXPORT(void)
_nc_linedump(void)260 _nc_linedump(void)
261 /* dump the state of the real and virtual oldnum fields */
262 {
263 static size_t have;
264 static char *buf;
265
266 int n;
267 size_t want = (screen_lines + 1) * 4;
268
269 if (have < want)
270 buf = typeMalloc(char, have = want);
271
272 (void) strcpy(buf, "virt");
273 for (n = 0; n < screen_lines; n++)
274 (void) sprintf(buf + strlen(buf), " %02d", OLDNUM(n));
275 TR(TRACE_UPDATE | TRACE_MOVE, (buf));
276 #if NO_LEAKS
277 free(buf);
278 have = 0;
279 #endif
280 }
281 #endif /* defined(TRACE) || defined(SCROLLDEBUG) */
282
283 #ifdef SCROLLDEBUG
284
285 int
main(int argc GCC_UNUSED,char * argv[]GCC_UNUSED)286 main(int argc GCC_UNUSED, char *argv[]GCC_UNUSED)
287 {
288 char line[BUFSIZ], *st;
289
290 #ifdef TRACE
291 _nc_tracing = TRACE_MOVE;
292 #endif
293 for (;;) {
294 int n;
295
296 for (n = 0; n < screen_lines; n++)
297 oldnums[n] = _NEWINDEX;
298
299 /* grab the test vector */
300 if (fgets(line, sizeof(line), stdin) == (char *) NULL)
301 exit(EXIT_SUCCESS);
302
303 /* parse it */
304 n = 0;
305 if (line[0] == '#') {
306 (void) fputs(line, stderr);
307 continue;
308 }
309 st = strtok(line, " ");
310 do {
311 oldnums[n++] = atoi(st);
312 } while
313 ((st = strtok((char *) NULL, " ")) != 0);
314
315 /* display it */
316 (void) fputs("Initial input:\n", stderr);
317 _nc_linedump();
318
319 _nc_scroll_optimize();
320 }
321 }
322
323 #endif /* SCROLLDEBUG */
324
325 /* hardscroll.c ends here */
326