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Long Iray Render Times

ebergerlyebergerly Posts: 3,255
in Daz Studio Discussion

Wow. Working on an interior scene, fairly well lit (certainly not dark) and it took 40 minutes to show more than 0% progress for the Iray render. 

It's a fully furnished interior house scene with 4 rooms. And I'm trying to figure exactly what it is that's causing the delay. Could it be calculating lots of bounces in rooms far away from the render camera's field of view? Does it do any optimizing to neglect areas of the scene that are pretty much irrelevant? I think I also cranked the bounces down to 8 for the render. 

Hmm...

Comments

  • nonesuch00nonesuch00 Posts: 18,293
    edited July 2017

    That's normal for such long render times if you are CPU rendering. Are you sure your scene fits into your video card's memory?

    Post edited by nonesuch00 on
  • evilded777evilded777 Posts: 2,465
    edited July 2017

    If the camera doesn't see it, it really does not calculate it (unless there is some direct impact on what the camera does see).

     

    The real question is: 'fairly well lit' by what? You say its interior. Are you relying on light through windows and doors? That would be problem number one. Are you relying on emissive surfaces for lights? That could be problem number two. Sounds like a big set, does it fit in the memory of your graphics card? That could be problem number three.

    Post edited by evilded777 on
  • ebergerlyebergerly Posts: 3,255

    This is totally rendering on my GTX 1070 (8 GB memory), and I'm monitoring my CPU (8 logical cores) and they are down at 20-30% during the render. So the CPU isn't involved. For lighting I have interior lights (surface emissive) at 20,000 lumens. Lots of light. Not relying whatsoever on outside light thru windows.

    Also, I'm sure it's all on my GPU since I recall seeing something like 350MB of scene memory, so not even close.  

    Path length 8, Speed optimization. 

    I dunno. Strange....

  • ToborTobor Posts: 2,300

    Hard to tell without an example screenshot, but it sounds like the light is indirect, in which case render times can balloon. Max PathLength can be used to reduce render times for things like reflections, but won't have as much useful affect for indirect.

    Assuming the culprit is indirect light, there are numerous ways to improve render speeds:

    1. If the scene is mostly ambient (no shadows), see if you can lop off the top of the set and use the environment dome as a primary *direct* light source. Pick an HDRi image that has an indistinct light source. That's not hard. You can even create one yourself by producing a 1000x2000 pixel flat gray image in a graphics program. 

    2. Add supplementary direct lights that can be balanced in a way that the viewer is not aware of the additional light sources.

    3. Turn on the Architectural Sampler. It was designed for exactly this. This may not speed up render times overall, but the render may exhibit lower overall noise.

    4. Read up on the light portals feature that came out in 4.9. It allows you to build an invisible "window" that carries light external to the set inside. There's so far little documentation on it, so be prepared to experiment. Start here:

    http://docs.daz3d.com/doku.php/public/software/dazstudio/4/new_features/start

     

  • ebergerlyebergerly Posts: 3,255

    I think I may have found the culprit...or at least partial culprit.

    While tweaking things in this scene (killing unnecessary lights in other rooms, etc.), I saw that my CPU's were pegged, but my CPUID software said the GPU was at 2% utilization. HUH??

    So I quit D|S, now I've re-started. I'm thinking this may be a similar issue to what someone else had posted recently regarding D|S/Iray suddenly switching to CPU rendering even though GPU only was selected.

    I'll move this discussion to that thread...

  • ebergerlyebergerly Posts: 3,255

    I'm probably the only one who didn't know this, but....

    I finally realized that if you're doing an indoor scene, with a ceiling, and you have outside lighting (like HDR environment and/or a distant light, etc.), your render times could be astronomical compared to not using any exterior lighting. 

    I'm talking differences of like 40 minutes to render with outdoor lighting vs. 7 minutes without any outdoor lighting. 

    I guess all the calculations of the exterior light coming in thru glass windows and bouncing all over the interior takes a lot of calculating? I dunno, but from now on outside lights are banned from my indoor scenes. 

    Wow. I feel dumb. 

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