My scene takes too long to render

[PacoChan]

Hello everyone!

First post here but I've been using Corona for a while. I love its results.

I'm working on a retro point & click adventure game with pre-rendered backgrounds. All of them have been rendered with Corona and I'm very happy with their results. But I'm working on a scene now that will also require a small animation, but it takes too long to clear the noise.

It's still not finished but this is the basic setting: long big metal corridor with volumetric fog and a lot of lights that generate god rays through the fans. This render is the result after two hours. After 3/4 hours it's not much better. Other environments I can render them just fine in just half an hour (they don't have volumetric fog). I've tried with less lights, even with the fog disabled, but it still takes quite a while. Oh BTW, that render is without secondary solver and the volumetric fog is with single bounce enabled.

The thing is, is there some trick, or some setting that can help optimize this kind of setup? If I can, I'd like to preserve the fog and scale of the scene.

Thanks in advance!

[PacoChan]

After a lot of time investigating, I managed to solve my issue. I can make renders with acceptable quality in 1 hour. The problem was that I was using meshes with CoronaLightMtl as lights. Changing to disc lights and replicating their parameters, noise gets cleared a lot faster.

What I don't understand is, aren't they supposed to be the same? The documentation says that using a CoronaMtl with emissive is slow and shouldn't be used as a main light, but a CoronaLightMtl should be exactly the same as a Corona Light. So why was CoronaLightMtl giving me those poor results? I'm using Corona 1.6.3 btw.

[Ondra]

yes, they should. if you provide scene, we can investigate it

[PacoChan]

Sorry for the delay. I have uploaded a simplified version of the project, it is named: 1507602315_Lights-Test.zip

These are the results after 1min render, one with lights and one with CoronaLightMtl. It is clearly better the top image. The scene is ready to test both cases.

[maru]

Could it be because the geometry us more detailed than the lights?
Other than that, the scene could be probably optimized to cut render times. Materials are interesting - maybe they are too reflective? Also using rayswitch material could probably help, as the GI could be simplified.

[PacoChan]

The geometry of the light is very similar.

However I discovered a trick that made my scene to render A LOT faster. For some reason, the grid on the walkway was the biggest performance issue. I don't know why. Even though it's completely 3D, it doesn't have so many polygons. I discovered it because I noticed that it was a lot slower from a specific camera angle where the grid filled more of the screen. Just hiding it made render more than twice faster. I tried to fill the area with a sphere of even more polygons and it was as fast. So it isn't related to number of polygons. So, I don't know what happened there. But since the grid wasn't going to be seen from too close, I replaced it with a plane with opacity and normal map recreating the old grid and it works great.

It would be nice to know the reason to learn for future projects, or in order to fix it in case it's some kind of bug, but on my part I'm able to keep with working on my scene.

Thanks for the support!

[PROH]

Hi. Have you checked if there are coplanar faces in the grid model? This does slow down render times (in all renderer).

[PacoChan]

Hi. Have you checked if there are coplanar faces in the grid model? This does slow down render times (in all renderer).

Hi!

There aren't coplanar faces. There's a lot of intersecting geometry, sure, but not coplanar.