Make animation loop more understandable.
Change-Id: I71215e8f36abe82e591ec35880962628827a4b6f
BUG=10292
TEST=ran the program
Review URL: http://codereview.chromium.org/6019001
diff --git a/src/ply-image.c b/src/ply-image.c
index 58e1dae..3395c92 100644
--- a/src/ply-image.c
+++ b/src/ply-image.c
@@ -489,33 +489,27 @@
ply_image_free (image);
}
-/*
- * Compute the difference in nanoseconds between two timevals. Return 0 if the
- * clock is not reliable.
- */
-int64_t difference_nsec(struct timespec x, struct timespec y)
+
+int64_t timespec_to_nsec(struct timespec ts)
{
- int64_t z;
-
- if (bad_clock)
- {
- return 0;
- }
-
- z = x.tv_sec - y.tv_sec;
- z *= BILLION;
- z += x.tv_nsec - y.tv_nsec;
- return z;
+ int64_t nsec;
+ nsec = ts.tv_sec;
+ nsec *= BILLION;
+ nsec += ts.tv_nsec;
+ return nsec;
}
-void gettime_check(struct timespec *ts)
+int64_t gettime_check(void)
{
- int r = clock_gettime(CLOCK_MONOTONIC, ts);
+ struct timespec ts;
+ int r = clock_gettime(CLOCK_MONOTONIC, &ts);
if (r)
{
bad_clock = 1;
+ return 0;
}
+ return timespec_to_nsec(ts);
}
@@ -584,9 +578,8 @@
/*
* Animate frames.
*/
- struct timespec then, now;
- int64_t error_nsec;
- int64_t interval_nsec;
+ int64_t draw_time_nsec, frame_period_nsec;
+ int64_t sleep_time_nsec, now_nsec, then_nsec;
xoff = strtol (argv[2], &endptr, 10);
if (endptr == argv[2] || *endptr != '\0')
@@ -603,33 +596,39 @@
* Begin animation.
*
* The first time around, we don't know how long it takes to draw a
- * frame, so we assume it's instantaneous. After that, we assume
- * that the drawing time for the previous cycle is a good estimate
- * for the next cycle. Errors may be introduced by different frame
- * size and complexity (PNG decoding).
+ * frame, so we approximate it as 0. After that, we assume that the
+ * drawing time for the previous cycle is a good estimate for the
+ * next cycle. Errors may be introduced by different frame size and
+ * complexity (PNG decoding) and by the CPU load.
*/
- error_nsec = 0;
- interval_nsec = BILLION / frame_rate;
- gettime_check (&now);
+ draw_time_nsec = 0;
+ frame_period_nsec = BILLION / frame_rate;
+ now_nsec = gettime_check ();
for (i = 4; i < argc; i++)
{
/*
- * Before displaying the next frame, sleep for the inter-frame
- * interval, adjusted by the error in the previous cycle.
- * Positive error means the last cycle took longer than desired.
+ * Before displaying the next frame, sleep for the right amount
+ * of time so that the achieved period approximates the desired
+ * period.
*/
- if (interval_nsec - error_nsec > 0)
+ sleep_time_nsec = frame_period_nsec - draw_time_nsec;
+ if (sleep_time_nsec > 0)
{
struct timespec req;
- req.tv_sec = (interval_nsec - error_nsec) / BILLION;
- req.tv_nsec = (interval_nsec - error_nsec) % BILLION;
+ req.tv_sec = sleep_time_nsec / BILLION;
+ req.tv_nsec = sleep_time_nsec % BILLION;
nanosleep (&req, NULL);
}
ply_frame_buffer_show_file_at_xy (buffer, argv[i], xoff, yoff);
- then = now;
- gettime_check (&now);
- error_nsec = difference_nsec (now, then) - interval_nsec;
+ then_nsec = now_nsec;
+ now_nsec = gettime_check ();
+ /*
+ * If the clock is bad (unlikely), assume draw time is
+ * instantaneous as a rough guess.
+ */
+ draw_time_nsec = bad_clock ? 0 :
+ now_nsec - then_nsec - sleep_time_nsec;
}
}
}
