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Thread: LW 2018.0.2: Very High Render Time of <100% Opacity Metallic Objects

  1. #1
    gold plated 3D Chrusion's Avatar
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    LW 2018.0.2: Very High Render Time of <100% Opacity Metallic Objects

    What should the render time of rough, metallic objects, that take up 60% of a 1920x1080 frame, be when one that is in front of another is set to 50% opacity (not transparency)? Normally, at full opacity, the scene renders in 30 mins. Is 4 - 5 hours typical? Or should it only be slightly longer, like 40 mins? Or should opacity really not put a hit on rendering? Scene is lit by one env. light, one distant light, and no GI. It reflects a Textured Environment HDR sky pano image. The slightly metallic objects are above a large, displaced terrain mesh.

    I got in "trouble" in another venue for saying motion blur was broken, when it was something unknown about the 2015-made terrain mesh, converted by 2018, that was to blame. I found that out, by process of elimination, after remaking the mesh in 2018, because I was getting similar, multi-hour render times with MB turned on, when times were 20-40 mins without MB. The new mesh solved that problem, so now I'm advancing on to doing object dissolve ramps in a new anim and I'm wondering if LW 2018's conversion of LWO2 objects to LWO3 format is introducing some sort of random issue that's causing different parts of the render engine to spaz out. It's one thing to rebuild a simple, subdivided mesh... it's quite another to rebuild an entire inventory of dozens of complex machinery models composed of 30-50 layers and 0.5 to 1 million polys.
    Dean A. Scott, mfa
    Senior 3D Animator and Graphic Design Illustrator, @ Astec, Inc.
    Owner / Lead Artist @ chrusion | FX

  2. #2
    Electron wrangler jwiede's Avatar
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    Quote Originally Posted by Chrusion View Post
    What should the render time of rough, metallic objects, that take up 60% of a 1920x1080 frame, be when one that is in front of another is set to 50% opacity (not transparency)? Normally, at full opacity, the scene renders in 30 mins. Is 4 - 5 hours typical? Or should it only be slightly longer, like 40 mins? Or should opacity really not put a hit on rendering? Scene is lit by one env. light, one distant light, and no GI. It reflects a Textured Environment HDR sky pano image. The slightly metallic objects are above a large, displaced terrain mesh.
    That's odd. Off the top of my head, I don't see why Opacity should cause such an extreme (8-10x) hit to render perf. Transparency would cause a perf. hit, but even for transparency an 8-10x hit seems unreasonable.

    You should probably package up and send the scene to support, and ask them why the object's opacity is generating such an extreme impact on render times.
    John W.
    LW2015.3UB/2018.0.7 on MacPro(12C/24T/10.13.6),32GB RAM, NV 980ti

  3. #3
    gold plated 3D Chrusion's Avatar
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    Turns out the actual render time was 2.5 hrs, vs. the estimate after 30 min of rendering. I think I narrowed it down. I had reflection rays set to 6, in order to clean up some stubborn fireflies on a black, slightly specular, slightly bump mapped material. I set it to 4 and render time was reduced 30%. I'm also thinking that, because the two materials are metallic and the object faces are parallel to each other, I'm no doubt running into the "infinite mirror" effect (ray recursion is default at 6), coupled with the render hit to ray trace rough, diffuse reflections seen in rough, diffuse reflections. When the front object is fully opaque, the "infinite mirror" cannot be seen, thus rendering faster.
    Dean A. Scott, mfa
    Senior 3D Animator and Graphic Design Illustrator, @ Astec, Inc.
    Owner / Lead Artist @ chrusion | FX

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