Why do walls increase render time?

[frankjrmi]

I have an interior scene. Several high poly objects, glass, lights, environment, etc. When I render without walls, it completes in 1 minute 7 seconds. When I add walls, it completes in 9 minute 3 seconds. My walls are just 4 cubes (no filet) with a diffuse texture, no bump, no displacement, no specular, no reflection, etc. One note: my walls do have Booles in them for the window cutouts.

Here are my render settings:
Pathtracing
Max samples: 1024
Diffuse depth: 3
Specular depth: 5
Ray epsilon: 0.0001
Filter size: 1.2
Alpha shadows ON
Caustic blur: 0.02
GI clamp: 0.3
Alpha channel OFF
Keep environment ON
Path term. power 0.6
Coherent ratio: 0.2
Static noise OFF
Parallel samples 8
Max tile samples 16
Minimize net traffic ON
Adaptive sampling OFF
Camera imager LINEAR
Exposure 1
Gamma 2.2
Highlight compression 0
Natural response OFF
Vignetting 0
Saturation 1
Hotpixel removal 1
Gamma before response ON
Pre-multiply alpha OFF
Disable partial alpha OFF
Min. display samples 1
Dithering ON
White point PURE WHITE
Saturate to white 0

[frankjrmi]

Oh, and I forgot to mention that I've rendered several interior scenes in the past with render times in the 2-minute range with every object included. Thanks for any help or tips.

[rwalker]

Just a guess: additional light bounces.

You might try converting your wall-window structures to simpler geometry by checking "Create single object" in the Boole Object attributes then "Make Editable" the boole.

[frankjrmi]

Just a guess: additional light bounces.

You might try converting your wall-window structures to simpler geometry by checking "Create single object" in the Boole Object attributes then "Make Editable" the boole.

Thanks for the suggestion. I tried that and it didn't make a big dent in the render times. I did change the wall structure completely to a cube, made it editable, added line cuts to knock out the windows, and that cut my render time down from 9ish minutes to about 5ish minutes. Still trying to optimize.

[alexchopjian]

From my experience, enclosing a space will naturally increase render times. What ends up happening is that all of those objects that originally existed in a void, now have been enclosed, and lighting and shadows have more places they need to bounce. Geometry doesn't really matter at that point. Watch this video about pathtracing to help visualize what's happening in your scene https://www.youtube.com/watch?v=frLwRLS_ZR0

As for your settings, I noticed that adaptive sampling is turned off. If render times are becoming an issue, adaptive sampling is a quick and easy way to help decrease time dramatically. Something may look noise free to you, but Octane may not see it that way, and continue to render that area. With adaptive sampling, you get to tell Octane when a surface is "clean," and Octane will stop rendering that area, thus decreasing times . Here's a great document explaining adaptive sampling inside of Octane https://inlifethrill.com/adaptive-sampl ... ne-render/

[frankjrmi]

From my experience, enclosing a space will naturally increase render times. What ends up happening is that all of those objects that originally existed in a void, now have been enclosed, and lighting and shadows have more places they need to bounce. Geometry doesn't really matter at that point. Watch this video about pathtracing to help visualize what's happening in your scene https://www.youtube.com/watch?v=frLwRLS_ZR0

As for your settings, I noticed that adaptive sampling is turned off. If render times are becoming an issue, adaptive sampling is a quick and easy way to help decrease time dramatically. Something may look noise free to you, but Octane may not see it that way, and continue to render that area. With adaptive sampling, you get to tell Octane when a surface is "clean," and Octane will stop rendering that area, thus decreasing times . Here's a great document explaining adaptive sampling inside of Octane https://inlifethrill.com/adaptive-sampl ... ne-render/

Thank you for the resources! I'll check those out.

[ralf_breninek]

For sure additional walls increase the rendertimes depending on the bounces, because every light ray has to be calculated multiplied by the times it is reflected / reflected from an object. Therefore this is normal behaviour. BUT you can define how many bounces you let the computer calculate (speculardepth, glossy depth, diffuse depth) Thereby you can decrease the rendertimes but also the realism if you go to low.

Rendering is about finding the sweetspot between the look you want to achieve and the time you want to let render take