Glass shadows - render pass setup?


Lets say, a very simple scene:
Grid for the floor (just mid grey)
Sphere - slightly reflective, phong (doesn’t matter I guess)
Cylinder in front of the sphere - Glass material (arch mat), with some colour.
(wonderful eh !)

Light is coming from 1 point light (sunlight for ex), and ambience from HDR - essentially doesn’t really matter about that, as I guess the process will be the same for any system.
(not using FG/GI but AO for enviro)

Obviously I’m breaking my scene up into render passes for compositing later on.
The ‘beauty’ pass should show that the shadow from the glass is slightly coloured and not a coloured block.

So for the shadow pass - how do I set this up ?
I presume some kind of matte shading trickery or something.

Because what tends to happen is the shadow ends up just being a block of white, as it doesn’t seem to get information from the glass material, just the outline of the object.


Perhaps it could be advantageous to have the shadows combined with another pass that would have been separated?


just disable primary rays with an override. reflections (and if I’m not mistaken, FG and GI) are considered secondary rays, so without primary rays the ground will effectively be invisible, while the colored shadow remains. hopefully i understood your question correctly, if not maybe make a scene file and some screenshots :smiley:


I’m not using FG/GI for any of my work at this time, so could be best for me to upload a file to check out.
I’m only testing at the moment, so it’s not like this is a problem on an important scene I’m working on. But I like to try and test a method before committing to it, you know how it is. :thumbsup:


From reading this and your other thread, it seems you like to make things needlessly complicated.

Embrace simplicity, and save your nerves before its too late.


Haha, could be right.
But if you don’t try out some new ways of doing things, well…we’d all still be living in caves or some cack like that.

It probably sounds more complicated because I was trying to find my feet again in 3d, and XSI is quite a tricky one to leap back into.
Anyway, enough fluff talk.

I’ll chuck up a stupidly simple scene tomorrow morning.


Found out yesterday at some point that it’s the material on the ground that is stopping colours being shown (shadow mat), so I’m just trying to work it out at the moment.
It was definitely transparent, just not coloured.


The shadows are being used on another pass at the moment, so the colours are there with no problems (I didn’t specifically need to separate them in the first place).


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