Function ggez::timer::remaining_update_time

pub fn remaining_update_time(ctx: &mut Context) -> Duration

Returns the fractional amount of a frame not consumed by check_update_time(). For example, if the desired update frame time is 40 ms (25 fps), and 45 ms have passed since the last frame, check_update_time() will return true and remaining_update_time() will return 5 ms -- the amount of time "overflowing" from one frame to the next.

The intention is for it to be called in your draw() callback to interpolate physics states for smooth rendering. (see http://gafferongames.com/game-physics/fix-your-timestep/)