101cf1db3e380ffcce7ef28464dfc517d30354df
[experiments/fps-limit.git] / fps-limit.h
1 /*
2  * fps-limit - Some functions to limit frames per seconds
3  *
4  * Copyright (C) 2013  Antonio Ospite <ospite@studenti.unina.it>
5  *
6  * This program is free software: you can redistribute it and/or modify
7  * it under the terms of the GNU General Public License as published by
8  * the Free Software Foundation, either version 3 of the License, or
9  * (at your option) any later version.
10  *
11  * This program is distributed in the hope that it will be useful,
12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14  * GNU General Public License for more details.
15  *
16  * You should have received a copy of the GNU General Public License
17  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
18  */
19
20 #ifndef FPS_LIMIT_H
21 #define FPS_LIMIT_H
22
23 #include <stdio.h>
24 #include <string.h>
25 #include <time.h>
26
27 #ifdef DEBUG
28 #define dbg(...)                     \
29         do {                         \
30                 printf(__VA_ARGS__); \
31                 printf("\n");        \
32                 fflush(stdout);      \
33         } while(0)
34 #else
35 #define dbg(...) do {} while(0)
36 #endif
37
38 #define NSEC_PER_SEC 1000000000
39
40 #define timespecsub(a, b, result)                                \
41         do {                                                     \
42                 (result)->tv_sec = (a)->tv_sec - (b)->tv_sec;    \
43                 (result)->tv_nsec = (a)->tv_nsec - (b)->tv_nsec; \
44                 if ((result)->tv_nsec < 0) {                     \
45                         --(result)->tv_sec;                      \
46                         (result)->tv_nsec += 1000000000;         \
47                 }                                                \
48         } while(0)
49
50 struct fps_limit_stats {
51         struct timespec time_start;
52         struct timespec time_end;
53         unsigned int fps;
54 };
55
56 static void fps_limit_init(struct fps_limit_stats *stats, unsigned int fps)
57 {
58         memset(stats, 0, sizeof(*stats));
59
60         clock_gettime(CLOCK_MONOTONIC, &stats->time_start);
61         dbg("Init time: s: %ld, ns: %ld", stats->time_start.tv_sec, stats->time_start.tv_nsec);
62
63         stats->fps = fps;
64 }
65
66 static void fps_limit_sleep(struct fps_limit_stats *stats)
67 {
68         struct timespec elapsed;
69
70         dbg("Start time: s: %ld, ns: %ld", stats->time_start.tv_sec, stats->time_start.tv_nsec);
71
72         clock_gettime(CLOCK_MONOTONIC, &stats->time_end);
73         dbg("End time: s: %ld, ns: %ld", stats->time_end.tv_sec, stats->time_end.tv_nsec);
74
75         timespecsub(&stats->time_end, &stats->time_start, &elapsed);
76         dbg("Elapsed s: %ld ns: %ld", elapsed.tv_sec, elapsed.tv_nsec);
77
78         if (elapsed.tv_sec == 0 && elapsed.tv_nsec < NSEC_PER_SEC / stats->fps) {
79                 struct timespec remaining = {0, 0};
80
81                 /* remaining delay, _relative_ to time_end */
82                 remaining.tv_nsec = (NSEC_PER_SEC / stats->fps) - elapsed.tv_nsec;
83                 dbg("Sleeping for: ns: %ld", remaining.tv_nsec);
84
85                 clock_nanosleep(CLOCK_MONOTONIC, 0, &remaining, NULL);
86         }
87
88         /* update the stats for the next iteration */
89         clock_gettime(CLOCK_MONOTONIC, &stats->time_start);
90 }
91 #endif /* FPS_LIMIT_H */