Epic's GPUlightmass

[PrizmIzm]

@Luoshuang

1. Does the current lighting scenarios system work for you? What’s its problems?
2. This will probably be implemented in the form of ‘bake only selected objects’
3. This is unlikely to happen in near future. When we were implementing VLM streaming for 4.24 we thought about that possibility however we didn’t figure out a way without incuring significantly higher per-pixel cost compared to current system (especially when you combine it with volumetric fog). We may think about that again in the future.
4. This is on the list.

For the bugs, 1 and 2 are known and will be fixed in the following commits. 3 is new to me - was the editor compiling shaders when you ran GPULightmass? Does forcing a skylight recapture fixes it when the lower hemisphere option is on?

Thanks for the response, and good to known about the progress, I’m sure other people will want to know about these things. I’ll try and answer the best I can.

1. With CPU Lightmass you can bake a skylight in stationary mode and then adjust it’s own intensity + Indirect Lighting Intensity within a post process volume - that gives the effect of fading in / out a baked daylight scene. There are several limitations to doing this 1. When you fade down ‘Indirect Lighting Intensity’ in the postprocess volume, it fades out the influence of all baked lighting and volumetric light probes in the level - so if you’ve baked any other lights, they’re gone also. 2. This method can only contain one lightbake and not several different ones; so if you wanted to bake a day scene, an evening scene, and a night scene, and fade between them then you’re stuck. 3. CPU Lightmass is hugely inefficient and slow. I personally want to bake lighting for an open world town (indoors and outdoors), but the quickest I can get it down to (without loosing too much quality) is about 3 minutes per building! 4. CPU LM doesn’t allow me to just rebake the area I’m working on, so the idea of re-baking a whole town every time I change a single light is unthinkable.
2. This is VERY encouraging - such a simple fix would save thousands of people, thousands of hours!
3. This is a shame - the most simple system I could think that would cure a lot of woes would use the same probes that are in the editor right now, but just allow the drawing of a simple volume and for there to be a vertical and horizontal density slider which would populate the volume with a grid of probes. Another massive addition would be the ability to darken / lighten those probes after bake - this would allow artists to be able to exclude volumetric fog from indoor areas (another huge feature for a relatively simple change).
4. Awesome! I figured that would be a priority. My GPUs are ready.

Bugs

3. Editor was not compiling and I was using an SLS cubemap (not a captured scene) so there’s no way for me to recapture.

I hope all this helps. I can see real potential here once all your algos are in and the efficiency is up. I was a big fan of your independent GPULM, I’ve used it a lot.