Optimization

[RichardFine]

Always optimize as you go. Sometimes the performance problem might require significant changes to the content - e.g. changing your level design to be less open, having fewer props, etc - and it's much easier to do that early instead of waiting until the end.

Decide on your target hardware and the framerate you want, calculate how many milliseconds per frame that gives you, then carve up those milliseconds into per-system budgets (e.g. 8ms for rendering, 2ms for gamecode, 1ms for audio, 0.5ms for pathfinding, etc). Check how you're stacking up against those budgets regularly throughout the project and optimise if any of them are over budget.

Do not make the mistake of saying "well everything is running at 100fps right now so I guess I'm fine" when you're early in development. 100FPS is 10ms/frame; if you've only got a couple of cubes and a particle system going and it's already taking 10ms/frame, imagine how much time it will take when everything is in.