746c9575fa84c250057cba71b2302ac85ebcd48a
[experiments/fps-limit.git] / fps-limit.c
1 /*
2  * fps-limit - Example program 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 #include <stdio.h>
21 #include <time.h>
22
23 #ifdef DEBUG
24 #define dbg(...)                     \
25         do {                         \
26                 printf(__VA_ARGS__); \
27                 printf("\n");        \
28                 fflush(stdout);      \
29         } while(0)
30 #else
31 #define dbg(...) do {} while(0)
32 #endif
33
34 #define FPS 60
35
36 #define NSEC_PER_SEC 1000000000
37
38 #define timespecsub(a, b, result)                                \
39         do {                                                     \
40                 (result)->tv_sec = (a)->tv_sec - (b)->tv_sec;    \
41                 (result)->tv_nsec = (a)->tv_nsec - (b)->tv_nsec; \
42                 if ((result)->tv_nsec < 0) {                     \
43                         --(result)->tv_sec;                      \
44                         (result)->tv_nsec += 1000000000;         \
45                 }                                                \
46         } while(0)
47
48 int main(void)
49 {
50         struct timespec time_start;
51         struct timespec time_end;
52         struct timespec elapsed;
53         struct timespec remaining = {0, 0};
54
55         struct timespec tmp;
56
57         while (1) {
58                 clock_gettime(CLOCK_MONOTONIC, &time_start);
59                 dbg("Start time: s: %ld, ns: %ld", time_start.tv_sec, time_start.tv_nsec);
60
61                 dbg("Doing some work, max: %d", NSEC_PER_SEC / FPS);
62                 tmp.tv_sec = 0;
63                 tmp.tv_nsec = (NSEC_PER_SEC / FPS) * 2 / 3;
64                 nanosleep(&tmp, NULL);
65
66                 clock_gettime(CLOCK_MONOTONIC, &time_end);
67                 dbg("End time: s: %ld, ns: %ld", time_end.tv_sec, time_end.tv_nsec);
68                 timespecsub(&time_end, &time_start, &elapsed);
69                 dbg("Elapsed s: %ld ns: %ld", elapsed.tv_sec, elapsed.tv_nsec);
70                 if (elapsed.tv_sec == 0 && elapsed.tv_nsec < NSEC_PER_SEC / FPS) {
71                         remaining.tv_nsec = (NSEC_PER_SEC / FPS) - elapsed.tv_nsec;
72                         dbg("Sleeping for: ns: %ld", remaining.tv_nsec);
73                         clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &remaining, NULL);
74                 }
75         }
76
77         return 0;
78 }