Re: Buffer Channels with Transparency

["peter boeykens" <peter_b(at)skynet.be>]

reflections should not block out the surface beneath it, the way they do with "over".

I would NOT take the way reflections look on a standard phong shader in XSI as a reference for how they should look.

In cg, usually dark zones in reflections end up darkening the surface - which looks all wrong except in "mirrored reflection" (100% reflection)

 

I'm looking at the reflection of the window on my white fridge here, and dark zones simply do not show up in the reflections. (no light is being sent to actually get reflected.)

 

it definitely looks like an additive comp - though not at 100% - which is the way I usually comp reflections (not screen!).

 

You might need to darken the surface beneath it a bit before doing so, theory being that with more light getting reflected, less of it actually reaches the surface. Best control is by using the luminance of the reflections as a matte for a darkening CC, before adding the reflections. Dont overdo that darkening though.

 

Note that my approach does fit the case of mirrored reflections, that would be black underneath with reflections added in at 100%.

 

 

just my 2p

 

 

----- Original Message -----

From: Ahmidou Lyazidi

To: XSI(at)Softimage.COM

Sent: Wednesday, August 08, 2007 1:30 AM

Subject: Re: Buffer Channels with Transparency

simply over?

2007/8/7, Votch <megavotch(at)gmail.com>:

Thanks for the suggestion. BA_color_switcher works perfectly. From now on I'm looking at the BA collection for shader solutions before looking at the built in stuff :)

Now I just need to find the best formula to composite the reflection pass. Just adding reflection over doesn't produce an identical result. Any suggestions there?

V-

On 8/6/07, Schoenberger <XSI(at)digidragon.de> wrote:

 

Try to use the BA_color_switcher.

It supports transparencies and reflections for pass channels.

 

Otherwise, there is no workaround beside passes.

 

Holger Schönberger
technical director
The day has 24 hours, if that does not suffice, I will take the night

 

---

From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of Votch
Sent: Sunday, August 05, 2007 10:19 PM
To: xsi(at)Softimage.COM
Subject: Buffer Channels with Transparency

I've ran into a problem using buffer channels with transparency.

The built in diffuse, reflection, specular, and ambient channels don't respect transparency at all. So I setup a custom rendertree and duplicated the base phong shader 4 times while disabling each shader compononent (diff, spec, ref) respecfully in order  to re-create an expender version of the original shader tree. In this rendertree I piped each separated component into a render_Channel and then each render_Channel into a mix_8. When rendering out the buffers for this rendertree transparent parts of the shader are not represented correctly. In the transparent sections the "Main Buffer" rays are sampled.

The only way I've found to to separate  these shader components successfully with transparent objects is to use passes. Then it works like a charm.

Does anybody know of a workaround or a way to make this work? Buffers are a lot easier to manage and are faster to render. But without sampling transparency correctly buffers are useless.

I've attached 3 images illustrating the 3 above scenarios and their corresponding scene files.

Votch Levi