GPU Lightmass - I am totally lost

I am totally lost with the new GPU Lightmass. :frowning:

My questions in this video:

  • When is it baked?
  • How can I switch to my final baked version?
  • What lights are supported (Static, Stationary, Moveable)?
  • Why do the static lights not work in the mode
  • Ray Traced Global Illumination can not be baked?

Thank you so much for any little help - appreciate it!

Movable lights do not get baked

Post process does nothing to GPU Lightmass, adjusting the raytrace settings only affects realtime GI

Not sure why the static lights don’t work, bug I assume

Also the plugin is like… super beta. There are a lot of things that currently do not work. You can try reading through the last few pages of the thread hereto see some of the known issues.

Edit 2: Sorry I didn’t respond directly to each question, here they are:

  1. Soon as you press the button (assuming it has something to actually bake). If you turn realtime on you should see bars on all the surfaces and noisy lightmaps resolving.
  2. Don’t have to, it will automatically load it. With cpu lightmass if you’re working in the viewport it may prompt you to “apply” it but I dont believe that is required for GPULM
  3. Static and Stationary, same as CPU lightmass. Should note that the dynamic shadows will always override static shadows for stationary lights.
  4. No idea
  5. It does its own GI calculation, the realtime GI implementation does nothing for it.

okay… that explains a few things… just trying to collect a few of my findings.
Please correct me if there is something wrong.

  1. GPU Lightmass has it’s own GI (Ray Traced GI is it’s own independent GI)
  2. It seem you can see the “Baked” version when switching to Realtime: Off (Ctrl+R)
  3. I can’t see any bars on any surfaces and no noisy lightmaps resolving
  4. Stationary Light: Doesn’t seem to create any dynamic shadows for moveable objects
  5. Moveable Light: Does seem to cast a dynamic shadow (regardless)

also wanted to note:
I am testing Unreal Preview 2 - 4.26

  1. Yes. GI from gpu lightmass is static, it’s baked into a texture. Raytraced GI is realtime.
  2. You have to turn Realtime ON to see the lightmaps building in realtime
  3. See above, also I assume you turned virtual textures (and virtual texture lightmaps) on? You did not go over this setting in your video
  4. Are you sure you are not talking about static lights? Stationary lights will cast dynamic shadows (provided they are enabled in the light, which they are by default) but static lights will not
  5. This indicates to me that you have some other problem here, because moveable lights are completely ignored by lightmass. They may as well not exist. All of their lighting and shadowing is handled in realtime.

Hmm… but there is one thing…

if I want to get maximum performance, then obviously I don’t want to use any ray tracing.
For example: If I am going to package a game for best Real Time Performance - I package usually without any ray tracing.

Since Lightmass GPU requires Ray Tracing for baking. What’s the process right after?

  1. You bake the Lightmass GPU when Ray Tracing is on.
  2. Then you load the project again but turn off Ray Tracing in the Project Settings?
  3. And then you package?

Or how is this done?

gpu lightmass is so broken its not even ready to go yet…

The release notes for 4.26 has all the info for getting the raytracing stuff working… al lthe things u need to enable in the options… then a command to type in console to stop real time raytracing so you get most performance in baking the gpu lightmass raytracing

Okay, thanks everyone. I was running another test today using 4.26.4 Preview. The GPU Lightmass seems to be still broken. However I finally found a solution to bake with DX12 and then just the full bake with DX11. On top of it, it’s actually fantastic to use some dynamic lights. And for quick previews, the GPU Lightmass is incredible fast. Love it.

I get it… it’s not final yet. But this thing is rocking and very promising. Best Baking ever so far.

I will run some more tests and will post some of my results to keep everyone posted.
Also fantastic for VR Experiences. This is it, super stoked.


Sooooooooo… about that solution? :smiley:

@bernardRieder how did you made this work?


Did you found a solution for your dynamic lightning? I’ve stumbled upon a similar problem and im not quite sure if it has somthing to do with the GPU lightmas…

cheers :slight_smile: smile: