Z-Depth buffer

[sidewing]

Suppose you have many copies of 10 different objects. They are all scattered between each other. I want to render out 1 object type at the time. The problem is that when you put everything in je post production program, that the top layer wins (all those objects apprear in the front on top of all the other objects).

Is there a way to work with a Z-buffer such that the comp knows if the object is in front of another object?

John

[sidewing]

Here is a more precise idea as to what I want.

Image 1 is a composit of 2 different renders (per object type).
Image 2 is rendered with all objects visible.

I want to render in passes (layers). In other words: first 1 object type and then another. Then I want to go to AFX and composit all together. The problem is that the layer (in AFX) that is on top wins (so I get like image 1...).

How do I render per object type and composit all layers together such that they know their placement?

I have over 35 object types and over 250,000 objects. You see my problem?

John

[toby]

All you need to do is use matte objects. When rendering layer 1, keep all the objects in the scene, but change the surface of all the objects you don't want to see to jet-black, and make them not affect alpha.

The best way is to make copies of the objects with black surfaces, but you can use the 'matte object' feature in the object's properties panel. This can lead to bizarre render artifacts, so watch for them, especially if you multi-thread.

[sidewing]

Thanks!

When you say keep all objects in the scene do you mean all the different types of objects?

My issue is that the comp can not handle so many. We are talking about 1 million objects and 100 million polys. So I need to render 1 object type (about 5000 per object type) at the time, reload scene with ONLY particles and FX-Link 2nd particle to second object type (they all go through each other without bouncing).

Thanks,

John

[toby]

100 million?! :eek:
In that case, you'd be better off rendering in groups based on distance from the camera. Render all the types of objects together, the first group starting with the closest objects going back as far as the poly count allows - it's about 4 million max in my experience - then do the next group back and so on.

Actually, you should never need to render 100 million polys, that's many times more than can be displayed! Even at feature film res you'd have to make an effort to make good use of that many. Your first group render should be sufficient to copy and put in the background in AFX. You could render at double-size and then it will scale down all the way to the back and still fit in the view.

[sidewing]

Thanks Toby. I will do that. Indeed, it is a lot. Fortunately that is through the whole animation.

I just wished that you could render a z-buffer and put it in AFX such that it knows who goes on top of whom...

That case I could have rendered per object type.

Thanks

[toby]

There is a format that stores an object ID for use in AFX, I think it's the .RLA format. I've seen a tutorial, I'll see if I can find it.

[toby]

Well this is where it used to be, but it's down
http://www.dougplanet.com/tut-rla-fun.html

And this one only shows how to export from LW:
http://www.creativemac.com/2004/01_jan/tutorials/lw2ae1.htm

[sidewing]

That is an interesting tutorial Toby! Thanks.

I'm only afraid that it is based on DOF and that AFX is not smart enough to truly know placements of objects (and obstructs them) based on Z-depth.

I know that Timothy Alby once wrote in his book about z-depth and Digital Fusion. That program is really known for its integration with 3D.

Do you think that AFX is able to do what I want though?

Thanks

[toby]

I think so, but I don't really know for sure. I saw that tutorial, and it showed how each object in the render could be manipulated individually, although it was a dof tutorial, it looked like you could put something in front or behind other things. But thinking about it, it probably wouldn't do it automatically.

[sidewing]

Thanks.

I bought 2 extra gigs of memory and also ordered the HD Instance.

Early Christmas...

Thanks for all your help!

John

[lardbros]

I saw a tutorial somewhere, where they used object ID's within AFX and they could turn them off by just checking a checkbox for that object. It looked like it worked very well too.

[sidewing]

I will try object id as well... Indeed, I have heard about that one as well and have heard that LW 8.5 is stronger in that direction.

Thanks everyone.

I just bought HD-Instance and will ask a question in new thread. This was a plug that one of you suggested. I just bought it.

Thanks,

John