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 */