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27 ****************************************************************************/
29 /****************************************************************************
30 * Author: Zeyd M. Ben-Halim <zmbenhal@netcom.com> 1992,1995 *
31 * and: Eric S. Raymond <esr@snark.thyrsus.com> *
32 ****************************************************************************/
34 /******************************************************************************
37 hardscroll.c -- hardware-scrolling optimization for ncurses
40 void _nc_scroll_optimize(void)
45 This algorithm for computes optimum hardware scrolling to transform an
46 old screen (curscr) into a new screen (newscr) via vertical line moves.
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.
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.
61 Now, to a discussion of the line-move computation.
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.
68 Assume that the real screen starts with lines 0..23. Now, we have
69 the following possible line-oriented operations on the screen:
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.
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.
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.
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.
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.
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.
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
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.
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)
112 Use the following production:
114 hardscroll: hardscroll.c
115 $(CC) -g -DSCROLLDEBUG hardscroll.c -o hardscroll
117 Then just type scramble vectors and watch. The following test loads are
118 a representative sample of cases:
120 ----------------------------- CUT HERE ------------------------------------
122 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
125 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 -1
128 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
130 # An insertion (after line 12)
131 0 1 2 3 4 5 6 7 8 9 10 11 12 -1 13 14 15 16 17 18 19 20 21 22
133 # A simple deletion (line 10)
134 0 1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19 20 21 22 23 -1
136 # A more complex case
137 -1 -1 -1 -1 -1 3 4 5 6 7 -1 -1 8 9 10 11 12 13 14 15 16 17 -1 -1
138 ----------------------------- CUT HERE ------------------------------------
141 Eric S. Raymond <esr@snark.thyrsus.com>, November 1994
142 New algorithm by Alexander V. Lukyanov <lav@yars.free.net>, Aug 1997
144 *****************************************************************************/
146 #include <curses.priv.h>
148 MODULE_ID("$Id: hardscroll.c,v 1.41 2007/09/29 21:48:36 tom Exp $")
150 #if defined(SCROLLDEBUG) || defined(HASHDEBUG)
153 # define screen_lines MAXLINES
154 NCURSES_EXPORT_VAR(int)
156 # define OLDNUM(n) oldnums[n]
157 # define _tracef printf
159 # define TR(n, a) if (_nc_tracing & (n)) { _tracef a ; putchar('\n'); }
161 extern NCURSES_EXPORT_VAR(unsigned) _nc_tracing;
165 /* OLDNUM(n) indicates which line will be shifted to the position n.
166 if OLDNUM(n) == _NEWINDEX, then the line n in new, not shifted from
168 NCURSES_EXPORT_VAR(int *)
169 _nc_oldnums = 0; /* obsolete: keep for ABI compat */
172 # define oldnums SP->_oldnum_list
173 # define OLDNUM(n) oldnums[n]
174 # else /* !USE_HASHMAP */
175 # define OLDNUM(n) newscr->_line[n].oldindex
176 # endif /* !USE_HASHMAP */
178 #define OLDNUM_SIZE SP->_oldnum_size
180 #endif /* defined(SCROLLDEBUG) || defined(HASHDEBUG) */
183 _nc_scroll_optimize(void)
184 /* scroll optimization to transform curscr to newscr */
187 int start, end, shift;
189 TR(TRACE_ICALLS, (T_CALLED("_nc_scroll_optimize")));
191 #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
193 /* get enough storage */
194 if (OLDNUM_SIZE < screen_lines) {
195 int *new_oldnums = typeRealloc(int, screen_lines, oldnums);
198 oldnums = new_oldnums;
199 OLDNUM_SIZE = screen_lines;
201 /* calculate the indices */
204 #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
207 if (USE_TRACEF(TRACE_UPDATE | TRACE_MOVE)) {
209 _nc_unlock_global(tracef);
213 /* pass 1 - from top to bottom scrolling up */
214 for (i = 0; i < screen_lines;) {
215 while (i < screen_lines && (OLDNUM(i) == _NEWINDEX || OLDNUM(i) <= i))
217 if (i >= screen_lines)
220 shift = OLDNUM(i) - i; /* shift > 0 */
224 while (i < screen_lines && OLDNUM(i) != _NEWINDEX && OLDNUM(i) - i
229 TR(TRACE_UPDATE | TRACE_MOVE, ("scroll [%d, %d] by %d", start, end, shift));
230 #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
231 if (_nc_scrolln(shift, start, end, screen_lines - 1) == ERR) {
232 TR(TRACE_UPDATE | TRACE_MOVE, ("unable to scroll"));
235 #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
238 /* pass 2 - from bottom to top scrolling down */
239 for (i = screen_lines - 1; i >= 0;) {
240 while (i >= 0 && (OLDNUM(i) == _NEWINDEX || OLDNUM(i) >= i))
245 shift = OLDNUM(i) - i; /* shift < 0 */
249 while (i >= 0 && OLDNUM(i) != _NEWINDEX && OLDNUM(i) - i == shift)
251 start = i + 1 - (-shift);
253 TR(TRACE_UPDATE | TRACE_MOVE, ("scroll [%d, %d] by %d", start, end, shift));
254 #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
255 if (_nc_scrolln(shift, start, end, screen_lines - 1) == ERR) {
256 TR(TRACE_UPDATE | TRACE_MOVE, ("unable to scroll"));
259 #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
261 TR(TRACE_ICALLS, (T_RETURN("")));
264 #if defined(TRACE) || defined(SCROLLDEBUG) || defined(HASHDEBUG)
267 /* dump the state of the real and virtual oldnum fields */
271 size_t want = (screen_lines + 1) * 4;
273 buf = typeMalloc(char, want);
275 (void) strcpy(buf, "virt");
276 for (n = 0; n < screen_lines; n++)
277 (void) sprintf(buf + strlen(buf), " %02d", OLDNUM(n));
278 TR(TRACE_UPDATE | TRACE_MOVE, (buf));
281 #endif /* defined(TRACE) || defined(SCROLLDEBUG) */
286 main(int argc GCC_UNUSED, char *argv[]GCC_UNUSED)
288 char line[BUFSIZ], *st;
291 _nc_tracing = TRACE_MOVE;
296 for (n = 0; n < screen_lines; n++)
297 oldnums[n] = _NEWINDEX;
299 /* grab the test vector */
300 if (fgets(line, sizeof(line), stdin) == (char *) NULL)
305 if (line[0] == '#') {
306 (void) fputs(line, stderr);
309 st = strtok(line, " ");
311 oldnums[n++] = atoi(st);
313 ((st = strtok((char *) NULL, " ")) != 0);
316 (void) fputs("Initial input:\n", stderr);
319 _nc_scroll_optimize();
323 #endif /* SCROLLDEBUG */
325 /* hardscroll.c ends here */