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 delay, _relative_ to time_end */
  72                         remaining.tv_nsec = (NSEC_PER_SEC / FPS) - elapsed.tv_nsec;
  73                         dbg("Sleeping for: ns: %ld", remaining.tv_nsec);
  74                         clock_nanosleep(CLOCK_MONOTONIC, 0, &remaining, NULL);
  75                 }
  76         }
  77
  78         return 0;
  79 }