Alpha channel when using refractive material

[petfactory]

Hi !

I use a refractive glass material in combination with a lightdome with an hdr. I would like to get transparency in the glass parts as I would like to add the bg in post.
I have enabeled the checkbox invisible of the lightdome.

Is this possible or is it inherent to the refractive material ?

I get a solid alpha channel when I render ?
Any ideas ?

Thanks !

[Yannick]

In your material, have you tick the affect shadow option ( in the refraction section)?

[petfactory]

I am currently out of office, so I don´t have the scene infront of me but I am quite certain that I have both "affect shadows" enabeled as well as "color and alpha" channels selected in the refraction section.

I want to use a different background in the comp, not the one that I use as a texture of the lightdome. The background is stylized, a cartoon like background, so I am not going for realism there. But the render of the forground object will be rendered with the hdr IBL setup.

What I get is a solid alpha in the refractive parts of the object. The HDR from the domelight is refrected regardless if I enable the invisible checkbox of the domelight. Is there a way to limit the domelight texture from being rendered in the refractive pass. In other words I would like the background not to be visible through the refractive parts and leave some black in the alpha channel where you would see the background. I understand that this will be physically wrong since the comp background will not be refracted, but that will be ok. The visual is more important then real refractions. Maybe one solution would be to refract a uv pass and displace the bg in post, but that might be overkill.

I am relatively new to vray, so I might be missing something, so I am thankful for all input !

Thanks !

[vlado]

There is an "Affect channels" option in the refraction settings; set it to "color+alpha" and it should work. You may also need to set the dome light to be invisible to the camera.

Best regards,
Vlado

[petfactory]

I had all those things enabeled and dome invisible, but I realised that I had 0.99 in the refraction glossiness. That made the alpha solid. When I set it to 1 I get correct behaviour on the alpha channel.

# Johan

[petfactory]

So if I want the refarctive material to have a glossines lower then zero I will get a solid alpha ?
regardless if I set the affect alpha and color and alpha in the affect channels ?
I realize the inherant issue that the geo in the scene will be refracted and the bg in post will not be if an alpha is present in a render with a refractive material with a low glossiness.
I might be appraching it the wrong way, but what I would like is to have the domelight not to be present in the alpha if I set it to invisible ( and affect shad and color + alpha )

Regards,
Johan