Struggling with transition

[AndreasResch]

Hey.

After the recent great addition to Luxcore for Blender, I gave one of my actual project scenes a try and converted it to Luxcore. While the overall transition went quite well and I was able to implement all the features of my Cycles materials in Luxcore, I'm struggling with the rendering a lot.

My typical scenes are relatively low on polygons, but often use a lot of high-res textures and the output resolution can be between 6000px and 10000px on the longer side. In the scene I just converted it's similar. Quite few polygons (75K) but several high-res textures. Render resolution is 6000px by 4000px (for now).

The main problem is that I run out of GPU memory. My system has a GTX 1060 with 6GB RAM, whic is enough for my scenes with Cycles. If I use OpenCL, Blender just crashes. When using CUDA, I get a CUDA Out-Of-Memory error. The weird thing is, that the render preview works fine. But when I start the rendering the GPU memory shoots up to 5.7GB immediately and the renderings stop. Switching on the "Out of Core" option doesn't change anything. On my secondary PC, I have a GTX 970 TI (6GB as well) and the situation is the same. The question is - how can I get my rendering to cope with the GPU memory issue?

The other issue was, that my images haven't been written into the files correctly. The normal rendering was completely transparent and the shadow passes completely black. Although they are perfectly fine in the Image Viewer. But I will tackle that, once the GPU memory issue is solved.

Unfortunately I can't share any files as it's a commercial project that hasn't been released yet. But I will try to supply all information that I can.

[Sharlybg]

How much GPU memory that is require in your Blender cycles project ?
Does it work if you remove 1 or 2 high resolution textures from a material ?
For Out of core if the project doesn't in your 6gb vdeo memory you will require at least 32 gb to have any hope.

[AndreasResch]

Hey.

At some point, when I cut back on textures, it will start to run. But I need those and so I can't just delete them. But why does the scene start to render in render preview and not in the final rendering? And having 32GB GPU memory isn't an option of course. I won't invest several thousand of Euros, so that I can use Luxcore.

Meanwhile I test a little further and the issues are piling up. Some objects randomly turn black in rendering, being stuck in "Creating Render Session" forever sometimes and the before-mentioned file output issue. This looks like too much problems to overcome. The transition isn't as quick as I though. The functionality is very good though. Aside from the bevel shader, which is worked on already, I can pretty much realize all the materials that i use in Cycles as well. It's just that I can't render the final shot at the moment.

[Sharlybg]

Sorry for not clarifying that i was talking about System memory DDR3/4 or higher (because it is there that the engine load extra scene stuff when in Out of core mode ).

If the scene is rendering in viewport preview there are few that can explain this behaviour :

___ You are on cpu when rendering on the viewport look down in viewport setting (not general engine setting wic is upper)

___ Or you are on GPU viewport but some modifier (subsurf ) run on lower settings on viewport but when rendering the higher quality setting is choosen
killing the low remaining memory.

[AndreasResch]

Hey.

I have 64GB of system RAM - so that should not be the issue. But the "Out of Core" option didn't change a thing anyway. The scene either crashed (OpenCL) or I got the CUDA memory error.

I do have a subsurf modifier on 7 very small, low poly objects. They also have a Height Displacement in the material, but the subsurf levels are set the same for preview and final rendering. And as mentioned before, preview works perfectly fine. Also those objects are tiny. In the final rendering they have a screen space of 80px by 80px. And even if I delete those objects, the scene still was too much to handle.

Overall Luxcore seems to run better in 2.91 than in 2.92. In 2.92 I get stuck during "Create Render Session" quite often, while 2.91 seems to handle that better. I'll do a few more tests and whatever I find goes to the bug reports on Github - 3 are there already.

[Sharlybg]

Quite hard to tell without at least a small scene that reproduce the issue.
If you can reproduce the issue with a simple scene (cube ) a make it avalable we can better help you.

[AndreasResch]

Well. A simple cube will not run my GPU into memory issues.

Here's another interesting comparison.
On my work PC (GTX 1060) while being in Solid Mode, my GPU uses 2.3GB of memory. When I got to Render Preview mode, it goes up to 5.5GB - an increase of 3.1GB.
On my render PC (GTX 970 Ti) the solid mode needs 1.4GB of GPU memory. When switching to Render Preview mode, it goes up to 3.2GB - an increase of 1.8GB. During final rendering it goes up to 5.8GB though - so 2.6GB more than in Render Preview mode.

Thanks for your help.

[AndreasResch]

A little side question.

What's the reason that my Blender stats says 180K triangles and my Luxcore info line at render times says 1.5M Tris? No subsurfs in the scene.

[Sharlybg]

Well. A simple cube will not run my GPU into memory issues.

Blender nor Luxcore make a difference between a highly subdivided cube and a 3d scanned mountain. The point here is to setup a scene that mimic your current project complexity while keeping it simple. High poly count with big texture then we compare then on cycles and luxcore to spot the issue.

[Sharlybg]

A little side question.

What's the reason that my Blender stats says 180K triangles and my Luxcore info line at render times says 1.5M Tris? No subsurfs in the scene.

Are you running material displacement ?