Split out a header file so other projects can re-use the code

[experiments/fps-meter.git] / fps-meter.h

diff --git a/fps-meter.h b/fps-meter.h
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+++ b/fps-meter.h
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+/*
+ * fps-meter - Example program about how to measure 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_METER_H
+#define FPS_METER_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_meter_stats {
+       struct timespec time_start;
+       struct timespec time_end;
+       struct timespec elapsed;
+
+       unsigned int frames;
+       double nsecs;
+};
+
+static void fps_meter_init(struct fps_meter_stats *stats)
+{
+       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);
+}
+
+static void fps_meter_update(struct fps_meter_stats *stats)
+{
+       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, &stats->elapsed);
+       dbg("Elapsed s: %ld ns: %ld", stats->elapsed.tv_sec, stats->elapsed.tv_nsec);
+
+       stats->frames++;
+       stats->nsecs += (stats->elapsed.tv_sec * NSEC_PER_SEC + stats->elapsed.tv_nsec);
+       if (stats->nsecs >= NSEC_PER_SEC) {
+               /* 
+                * if we were garanteed that each frame took less than
+                * a second, then just printing 'frames' would be enough here,
+                * but if we want to cover the case when a frame may take more
+                * than a second, some calculations have to be done.
+                */
+               float fps = stats->frames / (stats->nsecs / NSEC_PER_SEC);
+               printf("(frames: %d, nsecs: %f) FPS: %.2f\n", stats->frames, stats->nsecs, fps);
+               stats->nsecs = 0;
+               stats->frames = 0;
+       }
+
+       /* update the stats for the next iteration */
+       clock_gettime(CLOCK_MONOTONIC, &stats->time_start);
+}
+#endif /* FPS_METER_H */