This variable limits the
valid range of the time_step variable to a minimum frame rate.
Below that frame rate, time_step stays constant,
limiting the maximum per-frame distance of movements.
0.1 .. 16
This variable only affects time_step, and can not be used to increase
the frame rate.
fps_min = 16; // on less than 16 fps time_step remains constant.
time_step, time_factor, fps_max, fps_lock, total_ticks, total_frames, wait