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Build Lightmass freezes

So.. Ive downloaded new Xoio's Berlin flat. I wanted to discover, how the lighning is setup, but i ran into a problem.

Whenever i try to buid the light, my PC completely freezes for about half an hour on 1.72%. After some time it unfreezes, but continue to work very laggy, and the progress stays 1.72%. I tried to set the number on Lightning Bounces from 100( O_o ) to 10, but that didn't helped me.

I use Promoted 4.7 version (downloaded 04.12.14). i7-4770, GTX770, 8gbDDR3.

Other projects works fine. But Berlin Flat do not building even in stable 4.6 release. So, what is the problem, and how can i fix it? Or i have to update my PC(buy some Ram, maybe. But huge 3d renders(V-ray, MentalRay e.t.s) go very well).

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asked Dec 04 '14 at 09:43 PM in Rendering

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avatar image AlFlakky Mar 02 '15 at 03:17 PM

Hello again!

I just tried to build default TP template and it has stuck. I have 8gb RAM. I tried to do same thing on my Surface Pro 2 Tablet with 4gb RAM and everything was fine.

So.. It can be the RAM, there is another problem, that I'm not able to build such scene. I used to build big terrains with many objects on it, but now cannot build a very simple scene. How to fix it??

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Hi AlFlakky,

More than likely you're running into an issue where it's running out of RAM when trying to build. Lightmass can use a lot of RAM to build especially if it's a complex setup. The ArchViz setups can be this way.

Something you may want to try before upgrading RAM though would be to increase the size of your virtual memory. When Lightmass runs out of usable RAM it will use virtual memory cache which can be extremely slow.

The scene has very high poly meshes and also uses (what I would consider high) large LM resolutions for all the meshes in the scene. While the lighting bounce differences are not going to greatly affect build times, with exception of the first build time that take the longest. The part that is probably taking the longest are that the quality is bumped up to 4.0 vs the default 1. This will greatly increase lighting builds.

As an example I'm building lighting on the project now to see how long it takes with my machine. I've setup Swarm Agent to network with 8 other computers on our team and I'm at 72% right now and it's been about 15 minutes building on Production build for lighting. This is compared to using default settings for Lightmass in World Settings and building lighting on Preview that only took a little over 5 minutes.

You cannot compare setups that use V-Ray and MentalRay to UE4 since they are both offline rendering solutions in comparison to UE4's realtime rendering.

I hope this helps clarify a little.


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answered Dec 08 '14 at 03:37 PM

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Tim Hobson ♦♦ STAFF
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avatar image AlFlakky Dec 08 '14 at 06:11 PM

Yeah, that helps! Thaks alot for answering.

By the way, it would be great, if Epic add Custom Light Map function, so people can easily set their own lightmap, rendered with, for example, with MentalRay. Now i have to use Texture*Lightmap in materials in order to set my shadows on the object, but there is two problems: 1) I have to use many materials or Instances, to make different shadows on the same objects. 2) I don't know how to make fully ambient light, so it will be like Unlit, but with reflection, normal etc support.

avatar image Tim Hobson ♦♦ STAFF Dec 08 '14 at 06:46 PM

Thanks AlFlakky, I know this has been requested before and there may be a ticket in for it as a feature. Thanks for the suggestions none-the-less.

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