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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 * and: Thomas E. Dickey 1996-on *
33 * and: Alexander V Lukyanov 1997-1998 *
34 ****************************************************************************/
36 /******************************************************************************
39 hardscroll.c -- hardware-scrolling optimization for ncurses
42 void _nc_scroll_optimize(void)
47 This algorithm for computes optimum hardware scrolling to transform an
48 old screen (curscr) into a new screen (newscr) via vertical line moves.
50 Because the screen has a `grain' (there are insert/delete/scroll line
51 operations but no insert/delete/scroll column operations), it is efficient
52 break the update algorithm into two pieces: a first stage that does only line
53 moves, optimizing the end product of user-invoked insertions, deletions, and
54 scrolls; and a second phase (corresponding to the present doupdate code in
55 ncurses) that does only line transformations.
57 The common case we want hardware scrolling for is to handle line insertions
58 and deletions in screen-oriented text-editors. This two-stage approach will
59 accomplish that at a low computation and code-size cost.
63 Now, to a discussion of the line-move computation.
65 For expository purposes, consider the screen lines to be represented by
66 integers 0..23 (with the understanding that the value of 23 may vary).
67 Let a new line introduced by insertion, scrolling, or at the bottom of
68 the screen following a line delete be given the index -1.
70 Assume that the real screen starts with lines 0..23. Now, we have
71 the following possible line-oriented operations on the screen:
73 Insertion: inserts a line at a given screen row, forcing all lines below
74 to scroll forward. The last screen line is lost. For example, an insertion
75 at line 5 would produce: 0..4 -1 5..23.
77 Deletion: deletes a line at a given screen row, forcing all lines below
78 to scroll forward. The last screen line is made new. For example, a deletion
79 at line 7 would produce: 0..6 8..23 -1.
81 Scroll up: move a range of lines up 1. The bottom line of the range
82 becomes new. For example, scrolling up the region from 9 to 14 will
83 produce 0..8 10..14 -1 15..23.
85 Scroll down: move a range of lines down 1. The top line of the range
86 becomes new. For example, scrolling down the region from 12 to 16 will produce
87 0..11 -1 12..15 17..23.
89 Now, an obvious property of all these operations is that they preserve the
90 order of old lines, though not their position in the sequence.
92 The key trick of this algorithm is that the original line indices described
93 above are actually maintained as _line[].oldindex fields in the window
94 structure, and stick to each line through scroll and insert/delete operations.
96 Thus, it is possible at update time to look at the oldnum fields and compute
97 an optimal set of il/dl/scroll operations that will take the real screen
98 lines to the virtual screen lines. Once these vertical moves have been done,
99 we can hand off to the second stage of the update algorithm, which does line
102 Note that the move computation does not need to have the full generality
103 of a diff algorithm (which it superficially resembles) because lines cannot
104 be moved out of order.
108 The scrolling is done in two passes. The first pass is from top to bottom
109 scroling hunks UP. The second one is from bottom to top scrolling hunks DOWN.
110 Obviously enough, no lines to be scrolled will be destroyed. (lav)
114 Use the following production:
116 hardscroll: hardscroll.c
117 $(CC) -g -DSCROLLDEBUG hardscroll.c -o hardscroll
119 Then just type scramble vectors and watch. The following test loads are
120 a representative sample of cases:
122 ----------------------------- CUT HERE ------------------------------------
124 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
127 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 -1
130 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
132 # An insertion (after line 12)
133 0 1 2 3 4 5 6 7 8 9 10 11 12 -1 13 14 15 16 17 18 19 20 21 22
135 # A simple deletion (line 10)
136 0 1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19 20 21 22 23 -1
138 # A more complex case
139 -1 -1 -1 -1 -1 3 4 5 6 7 -1 -1 8 9 10 11 12 13 14 15 16 17 -1 -1
140 ----------------------------- CUT HERE ------------------------------------
143 Eric S. Raymond <esr@snark.thyrsus.com>, November 1994
144 New algorithm by Alexander V. Lukyanov <lav@yars.free.net>, Aug 1997
146 *****************************************************************************/
148 #include <curses.priv.h>
150 MODULE_ID("$Id: hardscroll.c,v 1.42 2008/08/03 23:49:30 tom Exp $")
152 #if defined(SCROLLDEBUG) || defined(HASHDEBUG)
155 # define screen_lines MAXLINES
156 NCURSES_EXPORT_VAR(int)
158 # define OLDNUM(n) oldnums[n]
159 # define _tracef printf
161 # define TR(n, a) if (_nc_tracing & (n)) { _tracef a ; putchar('\n'); }
163 extern NCURSES_EXPORT_VAR(unsigned) _nc_tracing;
167 /* OLDNUM(n) indicates which line will be shifted to the position n.
168 if OLDNUM(n) == _NEWINDEX, then the line n in new, not shifted from
170 NCURSES_EXPORT_VAR(int *)
171 _nc_oldnums = 0; /* obsolete: keep for ABI compat */
174 # define oldnums SP->_oldnum_list
175 # define OLDNUM(n) oldnums[n]
176 # else /* !USE_HASHMAP */
177 # define OLDNUM(n) newscr->_line[n].oldindex
178 # endif /* !USE_HASHMAP */
180 #define OLDNUM_SIZE SP->_oldnum_size
182 #endif /* defined(SCROLLDEBUG) || defined(HASHDEBUG) */
185 _nc_scroll_optimize(void)
186 /* scroll optimization to transform curscr to newscr */
189 int start, end, shift;
191 TR(TRACE_ICALLS, (T_CALLED("_nc_scroll_optimize")));
193 #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
195 /* get enough storage */
196 if (OLDNUM_SIZE < screen_lines) {
197 int *new_oldnums = typeRealloc(int, screen_lines, oldnums);
200 oldnums = new_oldnums;
201 OLDNUM_SIZE = screen_lines;
203 /* calculate the indices */
206 #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
209 if (USE_TRACEF(TRACE_UPDATE | TRACE_MOVE)) {
211 _nc_unlock_global(tracef);
215 /* pass 1 - from top to bottom scrolling up */
216 for (i = 0; i < screen_lines;) {
217 while (i < screen_lines && (OLDNUM(i) == _NEWINDEX || OLDNUM(i) <= i))
219 if (i >= screen_lines)
222 shift = OLDNUM(i) - i; /* shift > 0 */
226 while (i < screen_lines && OLDNUM(i) != _NEWINDEX && OLDNUM(i) - i
231 TR(TRACE_UPDATE | TRACE_MOVE, ("scroll [%d, %d] by %d", start, end, shift));
232 #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
233 if (_nc_scrolln(shift, start, end, screen_lines - 1) == ERR) {
234 TR(TRACE_UPDATE | TRACE_MOVE, ("unable to scroll"));
237 #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
240 /* pass 2 - from bottom to top scrolling down */
241 for (i = screen_lines - 1; i >= 0;) {
242 while (i >= 0 && (OLDNUM(i) == _NEWINDEX || OLDNUM(i) >= i))
247 shift = OLDNUM(i) - i; /* shift < 0 */
251 while (i >= 0 && OLDNUM(i) != _NEWINDEX && OLDNUM(i) - i == shift)
253 start = i + 1 - (-shift);
255 TR(TRACE_UPDATE | TRACE_MOVE, ("scroll [%d, %d] by %d", start, end, shift));
256 #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
257 if (_nc_scrolln(shift, start, end, screen_lines - 1) == ERR) {
258 TR(TRACE_UPDATE | TRACE_MOVE, ("unable to scroll"));
261 #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
263 TR(TRACE_ICALLS, (T_RETURN("")));
266 #if defined(TRACE) || defined(SCROLLDEBUG) || defined(HASHDEBUG)
269 /* dump the state of the real and virtual oldnum fields */
273 size_t want = (screen_lines + 1) * 4;
275 if ((buf = typeMalloc(char, want)) != 0) {
277 (void) strcpy(buf, "virt");
278 for (n = 0; n < screen_lines; n++)
279 (void) sprintf(buf + strlen(buf), " %02d", OLDNUM(n));
280 TR(TRACE_UPDATE | TRACE_MOVE, (buf));
284 #endif /* defined(TRACE) || defined(SCROLLDEBUG) */
289 main(int argc GCC_UNUSED, char *argv[]GCC_UNUSED)
291 char line[BUFSIZ], *st;
294 _nc_tracing = TRACE_MOVE;
299 for (n = 0; n < screen_lines; n++)
300 oldnums[n] = _NEWINDEX;
302 /* grab the test vector */
303 if (fgets(line, sizeof(line), stdin) == (char *) NULL)
308 if (line[0] == '#') {
309 (void) fputs(line, stderr);
312 st = strtok(line, " ");
314 oldnums[n++] = atoi(st);
316 ((st = strtok((char *) NULL, " ")) != 0);
319 (void) fputs("Initial input:\n", stderr);
322 _nc_scroll_optimize();
326 #endif /* SCROLLDEBUG */
328 /* hardscroll.c ends here */