Input before or after update/draw?

Question

This is how I understood the game loop, and I wanted to know if I'm correct or not:

1) Draw/render -> input
CPU    |    GPU
------------------
Update |
Draw   |
Input  | Rendering

2) Input -> Draw/render
CPU        |    GPU
------------------
Input      |
Update     |
Draw       |
(nothing?) | Rendering

By rendering I mean updating the actual frame. What happens in the second case? Is the CPU doing nothing or is it checking input for the next frame already? Are there any differences from checking input before or after the update/draw part?

Answer 1

Whether you input, update, render or render, input, update is irrelevant. The loop will restart, so there is no difference. Same with whether you input, update, draw or update, draw, input(which becomes input, update, draw under the same logic). Now, if your blocking at the end for a swap or frame-sync, then you may have input lag to rendering if you receive input before the waiting.

Hence, I always input, update, and then render.

Answer 2

If i was you, i should multithread the whole thing, having a renderthreat and a enginethreat or whatever you want to call it