fps-meter.c

   1 /*
   2  * fps-meter - Example program about how to measure 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 NSEC_PER_SEC 1000000000
  35
  36 #define timespecsub(a, b, result)                                \
  37         do {                                                     \
  38                 (result)->tv_sec = (a)->tv_sec - (b)->tv_sec;    \
  39                 (result)->tv_nsec = (a)->tv_nsec - (b)->tv_nsec; \
  40                 if ((result)->tv_nsec < 0) {                     \
  41                         --(result)->tv_sec;                      \
  42                         (result)->tv_nsec += 1000000000;         \
  43                 }                                                \
  44         } while(0)
  45
  46 int main(void)
  47 {
  48         struct timespec time_start;
  49         struct timespec time_end;
  50         struct timespec elapsed;
  51
  52         struct timespec tmp;
  53
  54         unsigned int frames = 0;
  55         double nsecs = 0;
  56         float fps;
  57
  58         while (1) {
  59                 clock_gettime(CLOCK_MONOTONIC, &time_start);
  60                 dbg("Start time: s: %ld, ns: %ld", time_start.tv_sec, time_start.tv_nsec);
  61
  62                 /* simulate some workload of about 60fps */
  63                 dbg("Doing some work, which takes about %d ns", NSEC_PER_SEC / 60);
  64                 tmp.tv_sec = 0;
  65                 tmp.tv_nsec = NSEC_PER_SEC / 60;
  66                 clock_nanosleep(CLOCK_MONOTONIC, 0, &tmp, NULL);
  67
  68                 clock_gettime(CLOCK_MONOTONIC, &time_end);
  69                 dbg("End time: s: %ld, ns: %ld", time_end.tv_sec, time_end.tv_nsec);
  70                 timespecsub(&time_end, &time_start, &elapsed);
  71                 dbg("Elapsed s: %ld ns: %ld", elapsed.tv_sec, elapsed.tv_nsec);
  72
  73                 frames++;
  74                 nsecs += (elapsed.tv_sec * NSEC_PER_SEC + elapsed.tv_nsec);
  75                 if (nsecs >= NSEC_PER_SEC) {
  76                         /*
  77                          * if each frame takes less than a second, then just
  78                          * printing 'frames' is enough, but if we want to
  79                          * cover the case when a frame may take more than
  80                          * a second, some calculations have to be done.
  81                          */
  82                         fps = frames / (nsecs / NSEC_PER_SEC);
  83                         printf("(frames: %d, nsecs: %f) FPS: %.2f\n", frames, nsecs, fps);
  84                         nsecs = 0;
  85                         frames = 0;
  86                 }
  87         }
  88
  89         return 0;
  90 }