X-Git-Url: https://git.cworth.org/git?a=blobdiff_plain;f=metrics.c;fp=metrics.c;h=c52bf2ee6c3557dd6b8b41dda820ac24bced4e5b;hb=851d05230af70b4a2f1f5754607d13f84d371887;hp=36ef90bf1c86b661204745b83aced491e675ed84;hpb=5894ec5a66b9131c06f6caefd8ec0b267ad9eea3;p=fips

diff --git a/metrics.c b/metrics.c
index 36ef90b..c52bf2e 100644
--- a/metrics.c
+++ b/metrics.c
@@ -113,6 +113,28 @@ struct metrics
 	struct timespec cpu_time_ts;
 };
 
+/* Return (a - b) while accounting for the fact that between a and b,
+ * the counter may have wrapped around (with a maximum number of bits
+ * in the counter of GL_QUERY_COUNTER_BITS). */
+static uint64_t
+subtract_timestamp (uint64_t a, uint64_t b)
+{
+	GLint timestamp_bits;
+
+	glGetQueryiv (GL_TIMESTAMP, GL_QUERY_COUNTER_BITS, &timestamp_bits);
+
+	/* Note: "<<" isn't defined for the number of bits in the
+	 * type, and the compiler will punish you.
+	 */
+	if (timestamp_bits == 64)
+		return a - b;
+
+	if (b > a)
+		return (1ull << timestamp_bits) + a - b;
+	else
+		return a - b;
+}
+
 metrics_t *
 metrics_create (metrics_info_t *info)
 {
@@ -836,9 +858,11 @@ metrics_end_frame_pre_swap (metrics_t *metrics)
 		printf ("# frame: Frame_Number Frame_Time_milliseconds Frame_latency_milliseconds CPU_load GPU_load\n");
 	} else {
 		/* Subtract previous frame's times to get frame times. */
-		frame_time_ns = swap_end_timestamp - metrics->previous_swap_end_timestamp;
+		frame_time_ns = subtract_timestamp (swap_end_timestamp,
+						    metrics->previous_swap_end_timestamp);
 
-		latency_ns = swap_end_timestamp - metrics->swap_begin_timestamp;
+		latency_ns = subtract_timestamp (swap_end_timestamp,
+						 metrics->swap_begin_timestamp);
 
 		cpu_time = TIMESPEC_DIFF (metrics->previous_cpu_time_ts, metrics->cpu_time_ts);