Lighting can be computed in two ways.
The classic way of doing it is forward rendering. You basically have to rerender the scene for each light to compute the change in lighting, so your performance is cut by 1/# lights. It's hard to get above about 8 lights in a scene like this, but it doesn't really cause any other issues.
There's also deferred lighting, in which case lighting is deferred until the very end and just rendered on the final 2d image. Lighting is rendered at the resolution of the image, and you can do thousands of lights because it's more of a filter on the final image. However, it breaks anti aliasing and in general doesn't look as good as forward rendering.
Physics computations are unrelated to the lighting. The objects will be moved into the correct positions each frame prior to any lighting being rendered. You could just calculate positions every frame, but if things are non-deterministic (like dynamic physics) then you really don't want a variable number of calculations per second or the results could change. You also don't want to compute something very expensive more than needed, so linking to framerate would lower framerate too.
Thanks!
I still don't get how physics and lighting are unrelated. You were saying that the objects are positioned prior to the lighting. Positioning takes into account physics, no? then, it means that physics go before lighting, which is in contrary to what is said in the article/slides
I'm missing here something - sorry for the bother..
That's nothing new from what people (gamedevs as well as directly from AMD's engineers) have been saying for a long time. GCN is built for a Mantle-like API, as its uarch cannot be taken advantage of fully with DX11. It was a forward looking uarch, meant to last them a long time.
I am hoping in the not too distant future, I can buy a Zen APU with GCN 2 and HBM2, that would make for an awesome base for an expanding rig, ie. plug in a GCN 2 dGPU, DX12 games take advantage of both.
This thing is not new also. VLIW5 to VLIW4 was also around underutilizing..
What's annoying me is that this article comes only now. They have known it years ago!