UE4 - Increasing lightmap-resolution increases Build Time drastically!

EliasWick · Nov 2015

Greetings! I have some trouble with Unreal Engine 4. I've been playing around with lightmap resolution to find out what the best lightmap resolution for a model would be in order for it to look good! So I did the "Override lightmap resolution" from 64 to 2048 which is the gave me the best result for the model. My problem is that It increased my building time drastically. It went from 7 seconds to over 4 minutes, and I have a pretty powerful PC. (And I was using the Lighting Quality of "Preview"). I am currently using the 4.9.2 version of Unreal Engine 4.

If there is anyone who can help me out please type a comment!

Thanks!
//Elias Wick

Ispheria · Nov 2015

There's a thing just for Unreal questions here
http://polycount.com/categories/unreal-engine

sprunghunt · Nov 2015

This is normal for unreal. Four minutes is still a fairly fast build time. A production level that you would find in a modern FPS would take about 15-20 minutes to build.

You could try optimising your lightmap UVs for better packing so you can use a lower resolution. 2048 is pretty big. Here's some instructions.

https://docs.unrealengine.com/latest/INT/Engine/Content/Types/StaticMeshes/LightmapUnwrapping/index.html

Noren · Nov 2015

Render small for setup, bigger for final.
The new resolution means the lightmap has a thousand times more pixel compared to the old one, so the increase in rendertime doesn't look that bad.

EliasWick · Nov 2015

Thanks Ispheria I have now moved the Thread to the new category "Unreal Engine 4"

Thanks for the quick answers Sprunghunt and Noren! I realized that I will have around 20 - 50 lights in my final scene, and around 200 to 400 models. I changed 1 models Lightmap resolution to 2048, and the time increased with over 3 minutes. Lets say I have 200 models... Gosh, will the rendering time take days? How does it work? I mean, if I have more high resolutioned models in my scene will the rendering time increase with lets say 3 minutes per model? That will be 10 hours for 200 models with one light in the scene. I assume there is some matematical formula to how the rendering and light building works. But it does sound incredibly crazy.

ZacD · Nov 2015

2048 is overkill for most models, 512 or less should be enough for most assets. 2048 is 16x the resolution of 512. Also don't use preview to judge how a model will look, preview is really only there to get a rough idea of how the lighting is going to turn out, but is going to be really blotchy with a lot of seams and artifacts.

EliasWick · Nov 2015

Thank you ZacDonald!

UE4 - Increasing lightmap-resolution increases Build Time drastically!

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