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LVP doen't work on OSX

Hello, I'm working on a game where we need a global illumination and a fully dynamic one enable a faster iteration process that's why we decided to try LPV. The feature itself is good enough for what we need (okay colour bleeding, good tweak possibilities, not too demanding performance wise and fully dynamic).

The problem is that my team use all OS where unreal is available, I didn't try on linux (yet) but on OSX I couldn't make it work. Here is what I did to test the feature:

  • I created a third person blueprint project on UE4.16

  • added r.LightPropagationVolume = 1 in ConsoleVariables.ini and restarted the engine

  • made something like cornell box using 6 cube and a sphere Mesh all in movable

  • put the sunlight in movable and checked "dynamic indirect lighting"

  • enabled "force no precomputed lighting"

  • enabled show->visualize->Light propagation volume

  • add a postprocess Volume in unbound

  • set "Light propagation volume" intensity to 10 (to be sure tu not miss it)

  • check if show->light component->Global illumination is "true"

and I get this result: alt text

Which is obviously just direct lighting + the sky color and that's it, no color bleeding at all (maybe some highly dithered AO).

I've read multiple time that LPV aren't supported on OSX because their version of OpenGL (4.0) doesn't support compute shader. But OpenGL on OSX is dropped since a while now and unreal only use metal (which support compute shaders). So it would be great to get this very convenient feature that requires no building, very highly configurable (great for stylised render) and doesn't depend on any additional information placed by hand on the map. I'm not against another GI technique but I it must not requiere to place boxed and work on dynamic objects (it's limited on static meshes that's ok). I tried use lightmass but except performance wise it's inconvenient on almost every aspect (100% static, ignore dynamic object in the building, only "diffuse boost" to stylise render, requires placing boxes etc...) for a not so great result.

Product Version: UE 4.16
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asked Jul 12 '17 at 01:34 AM in Bug Reports

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avatar image NeWincpp Jul 18 '17 at 02:19 PM

Even if I didn't saw any fix about that on 4.17 I tried anyway. Still not working

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Hey NeWincpp,

So the short answer here, which you point out in your description is that OS X doesn't support the Direct X 11 compute shader, which is necessary for LPVs to work. Metal's compute shader is going to run a similar path, but still is not DX11. What you are seeing and reporting is expected, and the limitations are outlined in our documentation.

Light Propagation Volumes

These are also still considered experimental and not production ready, so even if you had the correct platform, it might not work well in your final project like you want. I would look at using Stationary Lights which have dynamic functionality, as well as the Post Process global illumination methods to manage and control your scene's lighting.

Thank you,

Andrew Hurley

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answered Jul 24 '17 at 09:12 PM

avatar image NeWincpp Jul 25 '17 at 01:41 AM

If by "stationary lights" you mean lightmasses it is very inefficient in term of pipeline (mainly because of the process of building it) and this is a mostly static technique. The "post process Global Illumination" is just a setting that setup how lightmass are displayed on the final render (the documentation). So there is no dynamic GI on OSX/linux (and nothing "production ready").

I hope you guys are working on a fully dynamic GI technique, I don't care if it's LPV, radiance hints, VXGI or Deep G-Buffers based stuff just please anything more dynamic than this lightmass T__T

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