animation fade in objects with back faces hidden

[cloudbreak]

Hi all - I've tried to search for this with no luck so apologies if I've missed the solution somewhere else.

 

I'm rendering a simple animation in vRay (no GI) with a building fading in from 0% visible to 100%. See attached (chapel_01.jpg) for how it looks mid animation. What I really need though is slightly tricky to explain. I need to not see the hidden geometry when it's fading in. I'm just changing the object's visibility in object properties at keyframes so at the moment it's 'ghosting' in whereas I need to not be able to see geometry behind. I've mocked up what I need in photoshop (chapel_02.jpg) and if the camera was static then I'd just compile in post but the camera has movement so I can't. Any ideas?

 

Any help very gratefully received. Thanks. Jonty.

Edited September 4, 2014 by cloudbreak

[Nicolai Bongard]

Maybe model the house again with only the exterior faces and make sure the material applied is not 2 sided?

[cloudbreak]

Thanks very much for the quick response Nicolai but the same model is needed for showing interior shots in a later animation so remodelling probably isn't a viable option. Thanks anyway - much appreciated.

[Nicolai Bongard]

That should not be a problem. Just later in the animation, after the fade in, perhaps even when the camera is not pointed at the house, just on one frame make the remodelled house invisible again and the original house with interior visible. From one frame to the next you should not notice it.

[cloudbreak]

Ah I see what you mean Nicolai - however I've got more buildings which I'm fading in and out and I'm not sure I've got time to remodel. Also even with interior faces deleted, you'd still see for example the back wall through the front one. I'm trying to avoid that, like in photoshop when you have a final rendered imaged and bring the trasparency from 0 to 100, you don't see through the object to rear walls etc, you just see a transparent version of the fully opaque render. See what I mean?

 

I think what I'll have to do, although I was trying to avoid it, is render the animation twice, once with the building hidden and again with the building fully visible and go from one to the other in Premiere. Bit of a pain as it means twice the render time so if anyone's got any other alternatives I'd love to hear them.

 

Cheers.

[Scott Schroeder]

Just render out one frame without the building and one frame with the building ONLY. That way that second building only pass will fly as far as render times. If you need shadows, just set up the proper matte objects. There is no need to fully render 2 frames of each pass.

 

Doing this in post is the best way to do it. I don't know why you want to avoid it.

[cloudbreak]

Great thanks Scott - good advice.

[Fooch]

Remodel for this shot / stage. split the shot up