Bug, or Feature - diffuse transmitter to simulate sanded gla

Headroom · Post by **Headroom** » Sat Oct 13, 2012 4:55 am

I've been wanting to post this question for a while now. I came across it almost a year ago when I started rendering my lighting system concepts a little more in detail. I came across this again when rending my latest creation:
http://www.indigorenderer.com/forum/vie ... =4&t=11916

So here are two images to illustrate what I am talking about. One is a photo and the other a rendering.

Te part of concern is the round acrylic glass disk that has the little acrylic rods solvent welded to it. The ends of these rods are not polished but just sanded. Can be seen in both images due to the sanded diffusing surface the glow quite nicely and provide another little point of interest on the lamps.

When building the lighting system I never thought about this and it was a nice surprise. Then, of course I hoped to be able to replicate this in Blendigo/ Indigo and found that I could do that through a combination of, one in Blender, and one in Indigo. I've not been able to reproduce this in Blender.

The glass disc and the glass cylinder are two separate meshes, with the glass cylinder protruding into the glass disc. As in in reality, in Indigo both have the same material assigned to them. Then I assigned a different material only to the end caps. I chose a clossy-specular, but I don't think it matters. What matters is that it needs to be a material that has a medium, e.g. Glass. Diffuse transparent does not have a medium, at least none shows up in Te Indigo UI when exported from Blender.

With that exported the little end caps on the acrylic rods remain black/ transparent as they would when polished. Now, heres's the trick where I am not sure what I am doing is entirely valid. I stop the render and change the material of the end caps only from glossy-specular to diffuse- transmitter and voilà, there are my nicely diffusing, glowing end caps.

Is there a way to make this work directly through Blendigo that I am not aware of ?
Is this even a valid - approach ?

StompinTom · Post by **StompinTom** » Sat Oct 13, 2012 5:12 am

Off-topic: That's some real nice lens glare in the second 'rendering'!

CTZn · Post by **CTZn** » Sun Oct 14, 2012 12:34 am

Although the option may not be available in blendigo, diffuse transmitter materials can now use a medium. The one the glossy transparent used was preserved when you switched to the diffuse transmiter.

This option was added as a faster alternative for glossy transparent materials precisely

Very nice work headroom, I was confused at first before the thumbnails... wich is wich !? impressive case study !

Headroom · Post by **Headroom** » Sun Oct 14, 2012 1:46 pm

Tanks.....well, thanks to Indigo, really. What an outstanding tool this is to do lighting analysis. I've always been interested in " how does it really look".
Aside from creating " nice pictures" I find Indigo quite useful to simulate reality.

It is good to know that what I was doing is a valid approach. I will ask Ono if its possible to add a check box ( or something of that nature) to the Blendigo interface, so this can be done directly from Blender.

CTZn · Post by **CTZn** » Sun Oct 14, 2012 2:35 pm

Just keep in mind that the medium doesn't confer reflectivity to the diffuse transmitter. I'm not sure how realistic this is, it's still an approximation of a glossy transparent material with an exponent of about 2.0 methinks.

Headroom · Post by **Headroom** » Tue Oct 16, 2012 1:43 pm

Aha. So it's a dirty little trick! Just kidding of course.

I believe the way I am using it in this particular case this is perfect example how to use this feature ( obviously by pure coincidence and not because i actually know what I am doing ) I have tried it before with glossy- specular and while the effect is there its not as immediate ( or fast ) and not Asa strong even after rendering it through the night. The diffuse transmitter approximation looks actually more realistic then the perhaps more physically correct glossy specular material.

Of course in this case the surface that this applies to is very small in comparison to the rest of the scene. I have place one for the LEDs in a translucent globe and let fit or ender through last night and currently I have one cooking with the same scene where I changed the glossy-specular to a diffuse transmitter in the Indigo UI.
I can already see, however, that in this case the diffuse- transmitter version looks rather implausible. Of I get around to it tomorrow I may post images perhaps to show what not do do

Tanks for the explanation BTW. Greatly appreciated!

Could we possibly add a little check box in the Blendigo interface like "Preserve medium" or so ?

CTZn · Post by **CTZn** » Tue Oct 16, 2012 2:53 pm

Well my explanations weren't really accurate, you are the one leading here

I believe the way I am using it in this particular case this is perfect example how to use this feature ( obviously by pure coincidence and not because i actually know what I am doing ) I have tried it before with glossy- specular and while the effect is there its not as immediate ( or fast ) and not Asa strong even after rendering it through the night. The diffuse transmitter approximation looks actually more realistic then the perhaps more physically correct glossy specular material.

Amen to that.

Headroom · Post by **Headroom** » Tue Oct 16, 2012 10:48 pm

So here is an example for what not to use a diffuse transmitter (with medium).