Transperancy with GI

[neilmclellan]

G'day everyone!!
Does anyone know of a way to get GI lighting to go 'through' glass?
At the moment I do 2 renders, one without glass for the correct lighting, and one with glass for reflections.
Turning on indirect light helps a bit, but u don't get the nice 'glow' from external sunlight on nearby walls and roof.
I haven't upgraded to #5 yet (it's in the mail so don't know if new version does this.
Thanks!!
Neil

[Pete Exxtreme]

hi,

Did you check the light thru transparency option in the render settings (not on by default)

[neilmclellan]

Yep, sure did - light thru transperancy works fine with all other types of lighting, just not GI.
It's basically as if, as far as GI is concerned, all glass objects are solid, but u can see through them, and they can reflect light.
Thanks Pete
Neil
PS if anyone wants to give it a quick bash, try something as simple as a box with one side missing, and put in a glass wall.
Render either from inside or outside, with and without the glass and you'll see what I mean.
I discovered this prob with the indoor lighting scene (which has no glass in any windows or doors) by whacking in some windows.

[Pete Exxtreme]

Are you using real lights, or Hdri image to provide the lighting of the scene ?

[neilmclellan]

Skydome with real light set to sunlight.
Neil

[neilmclellan]

Here are samples with and without glass in the windows.
Neil

[Pete Exxtreme]

I don't really know the effect you try to reach. As far as i see, the behaviour is correct with the window. Maybe you could increase the transparecy level in the window shader, or/and use a spot light, with an openess of 90°, so simulate a wide-range light ? (i don't remember the exact words, as i don't have Carrara in front of me).

[neilmclellan]

Thanx Pete, I know what u mean by wide range light, thats how I used to simulate reflected light entering windows.
It's a pretty subtle difference, I admit - but I'm a pedantic bugger!
The main points of difference are the lighting entering the small window at the rear (visible on the ceiling) and the ambient light that gives more depth to the architraves on the ceiling that comes from the windows.
Also a general loss of 'brightness' with the windows in.
I have transperancy set at 0.01, with reflection the only real 'evidence' of the windows.
I know I can simulate with extra lighting, but as Carrara does it automatically with skydome (without glass), I was hoping I was just missing something in the glass texture.

Thank you very much for responding (BTW - love your avatar

Oh, I've been a great admirer of your work for a while, just had a squizz at your gallery. I have 'Street of Venice" in my inspiration folder.
All the best, Neil

[Pete Exxtreme]

thanks

BTW just have a sneak peak at this nice work of Patrick Grimaldi.
http://www.eovia3d.net/showthread.php?t=1876

While it's a bit different of what you want to achieve, Patrick is showing a bit what's 'behind the curtains' a bit below in his thread. 3d is cheating, and maybe you could find something interesting in it ? Yep, it's french written, but there is the google translator on this site, and a few carrara screenshots..
I hope this help

[Charles]

There are two things that could cause the indirect lighting not to go through glass:

1 The transparency is done with alpha channel. This is a bug I just fixed. Indirect lighting was not going through alpha.

2 The transparency has refraction (the default glass shader has some). The reason for this is that caustics are supposed to handle that part of the lighting. However if caustics are off it does not work. I also fixed that for the next patch.

Anyway knowing that you should be able to work around the problem. If it still does not work, could you email me your file at charles@eovia.com

[neilmclellan]

Thanx Charles
The glass does have refraction, so I'll give it a go.
Neil

[neilmclellan]

Charles, u r a LEGEND!!
Your solution worked a treat.
Thank you very much, I just wish I had asked about this a long time ago.
Best Regards
Neil