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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 ****************************************************************************/
35 /******************************************************************************
38 hardscroll.c -- hardware-scrolling optimization for ncurses
41 void _nc_scroll_optimize(void)
46 This algorithm for computes optimum hardware scrolling to transform an
47 old screen (curscr) into a new screen (newscr) via vertical line moves.
49 Because the screen has a `grain' (there are insert/delete/scroll line
50 operations but no insert/delete/scroll column operations), it is efficient
51 break the update algorithm into two pieces: a first stage that does only line
52 moves, optimizing the end product of user-invoked insertions, deletions, and
53 scrolls; and a second phase (corresponding to the present doupdate code in
54 ncurses) that does only line transformations.
56 The common case we want hardware scrolling for is to handle line insertions
57 and deletions in screen-oriented text-editors. This two-stage approach will
58 accomplish that at a low computation and code-size cost.
62 Now, to a discussion of the line-move computation.
64 For expository purposes, consider the screen lines to be represented by
65 integers 0..23 (with the understanding that the value of 23 may vary).
66 Let a new line introduced by insertion, scrolling, or at the bottom of
67 the screen following a line delete be given the index -1.
69 Assume that the real screen starts with lines 0..23. Now, we have
70 the following possible line-oriented operations on the screen:
72 Insertion: inserts a line at a given screen row, forcing all lines below
73 to scroll forward. The last screen line is lost. For example, an insertion
74 at line 5 would produce: 0..4 -1 5..23.
76 Deletion: deletes a line at a given screen row, forcing all lines below
77 to scroll forward. The last screen line is made new. For example, a deletion
78 at line 7 would produce: 0..6 8..23 -1.
80 Scroll up: move a range of lines up 1. The bottom line of the range
81 becomes new. For example, scrolling up the region from 9 to 14 will
82 produce 0..8 10..14 -1 15..23.
84 Scroll down: move a range of lines down 1. The top line of the range
85 becomes new. For example, scrolling down the region from 12 to 16 will produce
86 0..11 -1 12..15 17..23.
88 Now, an obvious property of all these operations is that they preserve the
89 order of old lines, though not their position in the sequence.
91 The key trick of this algorithm is that the original line indices described
92 above are actually maintained as _line[].oldindex fields in the window
93 structure, and stick to each line through scroll and insert/delete operations.
95 Thus, it is possible at update time to look at the oldnum fields and compute
96 an optimal set of il/dl/scroll operations that will take the real screen
97 lines to the virtual screen lines. Once these vertical moves have been done,
98 we can hand off to the second stage of the update algorithm, which does line
101 Note that the move computation does not need to have the full generality
102 of a diff algorithm (which it superficially resembles) because lines cannot
103 be moved out of order.
107 The scrolling is done in two passes. The first pass is from top to bottom
108 scroling hunks UP. The second one is from bottom to top scrolling hunks DOWN.
109 Obviously enough, no lines to be scrolled will be destroyed. (lav)
113 Use the following production:
115 hardscroll: hardscroll.c
116 $(CC) -g -DSCROLLDEBUG hardscroll.c -o hardscroll
118 Then just type scramble vectors and watch. The following test loads are
119 a representative sample of cases:
121 ----------------------------- CUT HERE ------------------------------------
123 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
126 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 -1
129 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
131 # An insertion (after line 12)
132 0 1 2 3 4 5 6 7 8 9 10 11 12 -1 13 14 15 16 17 18 19 20 21 22
134 # A simple deletion (line 10)
135 0 1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19 20 21 22 23 -1
137 # A more complex case
138 -1 -1 -1 -1 -1 3 4 5 6 7 -1 -1 8 9 10 11 12 13 14 15 16 17 -1 -1
139 ----------------------------- CUT HERE ------------------------------------
142 Eric S. Raymond <esr@snark.thyrsus.com>, November 1994
143 New algorithm by Alexander V. Lukyanov <lav@yars.free.net>, Aug 1997
145 *****************************************************************************/
147 #include <curses.priv.h>
149 MODULE_ID("$Id: hardscroll.c,v 1.29 1998/02/11 12:13:57 tom Exp $")
151 #if defined(SCROLLDEBUG) || defined(HASHDEBUG)
152 int oldnums[MAXLINES];
153 #define OLDNUM(n) oldnums[n]
155 #define T(x) (void) printf x ; (void) putchar('\n');
158 #define OLDNUM(n) newscr->_line[n].oldindex
161 #endif /* _NEWINDEX */
162 #endif /* defined(SCROLLDEBUG) || defined(HASHDEBUG) */
165 void _nc_scroll_optimize(void)
166 /* scroll optimization to transform curscr to newscr */
169 int start, end, shift;
171 TR(TRACE_ICALLS, ("_nc_scroll_optimize() begins"));
174 if (_nc_tracing & (TRACE_UPDATE | TRACE_MOVE))
178 /* pass 1 - from top to bottom scrolling up */
179 for (i = 0; i < screen_lines; )
181 while (i < screen_lines && (OLDNUM(i) == _NEWINDEX || OLDNUM(i) <= i))
183 if (i >= screen_lines)
186 shift = OLDNUM(i) - i; /* shift > 0 */
190 while (i < screen_lines && OLDNUM(i) != _NEWINDEX && OLDNUM(i) - i == shift)
194 TR(TRACE_UPDATE | TRACE_MOVE, ("scroll [%d, %d] by %d", start, end, shift));
195 #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
196 if (_nc_scrolln(shift, start, end, screen_lines - 1) == ERR)
198 TR(TRACE_UPDATE | TRACE_MOVE, ("unable to scroll"));
201 #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
204 /* pass 2 - from bottom to top scrolling down */
205 for (i = screen_lines-1; i >= 0; )
207 while (i >= 0 && (OLDNUM(i) == _NEWINDEX || OLDNUM(i) >= i))
212 shift = OLDNUM(i) - i; /* shift < 0 */
216 while (i >= 0 && OLDNUM(i) != _NEWINDEX && OLDNUM(i) - i == shift)
218 start = i+1 - (-shift);
220 TR(TRACE_UPDATE | TRACE_MOVE, ("scroll [%d, %d] by %d", start, end, shift));
221 #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
222 if (_nc_scrolln(shift, start, end, screen_lines - 1) == ERR)
224 TR(TRACE_UPDATE | TRACE_MOVE, ("unable to scroll"));
227 #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
231 #if defined(TRACE) || defined(SCROLLDEBUG)
232 void _nc_linedump(void)
233 /* dump the state of the real and virtual oldnum fields */
239 size_t want = (screen_lines + 1) * 4;
242 buf = malloc(have = want);
244 (void) strcpy(buf, "virt");
245 for (n = 0; n < screen_lines; n++)
246 (void) sprintf(buf + strlen(buf), " %02d", OLDNUM(n));
247 TR(TRACE_UPDATE | TRACE_MOVE, (buf));
253 #endif /* defined(TRACE) || defined(SCROLLDEBUG) */
258 main(int argc GCC_UNUSED, char *argv[] GCC_UNUSED)
260 char line[BUFSIZ], *st;
263 _nc_tracing = TRACE_MOVE;
269 for (n = 0; n < screen_lines; n++)
270 oldnums[n] = _NEWINDEX;
272 /* grab the test vector */
273 if (fgets(line, sizeof(line), stdin) == (char *)NULL)
280 (void) fputs(line, stderr);
283 st = strtok(line, " ");
285 oldnums[n++] = atoi(st);
287 ((st = strtok((char *)NULL, " ")) != 0);
290 (void) fputs("Initial input:\n", stderr);
293 _nc_scroll_optimize();
297 #endif /* SCROLLDEBUG */
299 /* hardscroll.c ends here */