Light guide: inner reflection


#1

Hi people,
it is been a while that I’m testing with Appleseed and I think it is amazing.

I’m writing because I’d like to render a light-guide that, like an optical fiber, guides light around. I have trouble finding good render settings for it.
Can you …‘guide’ me?

Thank you
Rickyx


#2

Hey rickyx!

Just create your cylindrical segments, apply a glass shader to them and also activate caustics in order to guide the light inside the medium. And of course you need a light to shine one extreme.

What 3DCC plugin are you using?


#3

All good advice what Juan Carlos wrote. This is a tricky situation to render, especially if you want to use a small directed light source in a larger environment. Switch to Progressive Stochastic Photon Mapping in the lighting tab. Unidirectional path tracing is not well suited for this situation.


#4

Exactly, SPPM will help a lot in this case. Note that we have a restriction of 100 bounces today, but this restriction should not apply to photon tracing. I’ve opened a ticket to lift this limitation in the future: https://github.com/appleseedhq/appleseed/issues/1950


#5

Please tell us how everything turned out!


#6

Thank you!
I’m using Blender, I’ll post some results later.
Yes, the scene is quite extreme :wink:

Have a nice day,
Riccardo


#7

Yes, Blender is better in this case. In Max you cannot yet choose SPPM and I haven’t seen an export option for appleseed scene files there, though someone may prove me wrong on that. In Blender it’s possible to export a scene file and then use studio to adjust all settings, even the ones which are not exposed in Blender but the core engine features.


#8

It’s true that SPPM is not exposed in appleseed-max yet. We’ll add that.

You can however export appleseed scenes from appleseed-max:


#9

Here is a quick test scene (the modernized version of a scene I did in 2010):
fiber.zip (3.1 MB)

It includes the source scene as a 3ds Max 2017 file and a ready-to-render appleseed scene manually setup to use SPPM.

Here is a test render:

There is currently a small issue in appleseed: it will emit warning messages when reaching the maximum number of bounces. We’ll need to allow disabling these warnings since they cost a lot of performance. For the time being, you can set log severity to error in settings/appleseed.studio.xml:

<parameter name="message_verbosity" value="error" />

#10

Great, I knew I may have missed something. I looked at File->Export (works for Arnold) and in save file under the render tab and didn’t see a suitable option.


#11

Good point, we’ll try to add appleseed export under File -> Export.


#12

Nice scene @franz I really like test scenes like this. SPPM for max would be cool :smiley:


#13

Thank you for helping me!

My blender parameters are as attached:
SPPM appears as “engine” and “direct lighting”. Am I doing right?

Have a nice day,
Riccardo!

BlenderParams|279x500


#14

It looks like your upload is broken.


#15

Should be visible now.


#16

Yes, these are the correct Engine and Light Sampler Settings. You may try under Direct Lighting the option “RT Direct Lighting” (ray traced direct lighting). Depending on the scene it may work better than “SPPM Direct Lighting”.


#17

@Jonathan_Dent Does Max Bounces = 0 mean unlimited bounces in SPPM’s Photon Tracing / Radiance Estimation parameters?


#18

I’m not sure. The sppm parameters have been around since before I started working on blenderseed and I haven’t played with them myself. I’ll check the code


#19

In the console I get:

2018-04-22T22:49:53.703917Z <006> 1398 MB warning | reached hard iteration limit (100), breaking path tracing loop.

whatever direct lightning.

Ricky


#20

@rickyx Yes, that’s a known issue, as I explained just above.