SDL_SetTimer — Set a callback to run after the specified number of milliseconds has
elapsed.
SDL provides several cross-platform functions for dealing with time.
It provides a way to get the current time, a way to wait a little while,
and a simple timer mechanism. These functions give you two ways of moving an
object every x milliseconds:
Use a timer callback function. This may have the bad effect that it runs in a seperate thread or uses alarm signals, but it's easier to implement.
Or you can get the number of milliseconds passed, and move the object if, for example, 30 ms passed.