+/*
+ * fps-limit - Some functions to limit frames per seconds
+ *
+ * Copyright (C) 2013 Antonio Ospite <ospite@studenti.unina.it>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef FPS_LIMIT_H
+#define FPS_LIMIT_H
+
+#include <stdio.h>
+#include <string.h>
+#include <time.h>
+
+#ifdef DEBUG
+#define dbg(...) \
+ do { \
+ printf(__VA_ARGS__); \
+ printf("\n"); \
+ fflush(stdout); \
+ } while(0)
+#else
+#define dbg(...) do {} while(0)
+#endif
+
+#define NSEC_PER_SEC 1000000000
+
+#define timespecsub(a, b, result) \
+ do { \
+ (result)->tv_sec = (a)->tv_sec - (b)->tv_sec; \
+ (result)->tv_nsec = (a)->tv_nsec - (b)->tv_nsec; \
+ if ((result)->tv_nsec < 0) { \
+ --(result)->tv_sec; \
+ (result)->tv_nsec += 1000000000; \
+ } \
+ } while(0)
+
+struct fps_limit_stats {
+ struct timespec time_start;
+ struct timespec time_end;
+ unsigned int fps;
+};
+
+static void fps_limit_init(struct fps_limit_stats *stats, unsigned int fps)
+{
+ memset(stats, 0, sizeof(*stats));
+
+ clock_gettime(CLOCK_MONOTONIC, &stats->time_start);
+ dbg("Init time: s: %ld, ns: %ld", stats->time_start.tv_sec, stats->time_start.tv_nsec);
+
+ stats->fps = fps;
+}
+
+static void fps_limit_sleep(struct fps_limit_stats *stats)
+{
+ struct timespec elapsed;
+
+ dbg("Start time: s: %ld, ns: %ld", stats->time_start.tv_sec, stats->time_start.tv_nsec);
+
+ clock_gettime(CLOCK_MONOTONIC, &stats->time_end);
+ dbg("End time: s: %ld, ns: %ld", stats->time_end.tv_sec, stats->time_end.tv_nsec);
+
+ timespecsub(&stats->time_end, &stats->time_start, &elapsed);
+ dbg("Elapsed s: %ld ns: %ld", elapsed.tv_sec, elapsed.tv_nsec);
+
+ if (elapsed.tv_sec == 0 && elapsed.tv_nsec < NSEC_PER_SEC / stats->fps) {
+ struct timespec remaining = {0, 0};
+
+ /* remaining delay, _relative_ to time_end */
+ remaining.tv_nsec = (NSEC_PER_SEC / stats->fps) - elapsed.tv_nsec;
+ dbg("Sleeping for: ns: %ld", remaining.tv_nsec);
+
+ clock_nanosleep(CLOCK_MONOTONIC, 0, &remaining, NULL);
+ }
+
+ /* update the stats for the next iteration */
+ clock_gettime(CLOCK_MONOTONIC, &stats->time_start);
+}
+#endif /* FPS_LIMIT_H */