Tracking Time Without Clock

As a plus one in a different domain, this is basically what I've done in a videogame I'm working on:

• The tick method is called at a known fixed rate. So none of that code needs to care about frame rate. Inputs are passed to this tick function with a timestamp on them for any cases where making the input between ticks would be noticeable.
• The draw function takes a parameter on how far between two different ticks the rendered frame is at.

As a result, the system interface that the game code calls into has zero functions related to getting the time.