day-night loop, dynamic skybox, clock on debug panel

src/util/timeutil.cpp

@@ -0,0 +1,14 @@
+#include "timeutil.h"
+
+float timeutil::time_value(float hour, float minute, float second) {
+    return (hour + (minute + second / 60.0f) / 60.0f) / 24.0f;
+}
+
+void timeutil::from_value(float value, int& hour, int& minute, int& second) {
+    value *= 24;
+    hour = value;
+    value *= 60;
+    minute = int(value) % 60;
+    value *= 60;
+    second = int(value) % 60;
+}