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Compositing: Advanced compositing at a smaller scale Added on: Sat Dec 14 2002 |
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 Matte/Shadow material: This is probably what you'll want to use most of the time, it's a material which makes the object invisible but kind of works as a 3D luminesence mask ie. any objects that goes behind it won't be seen since it protects that area and uses the background.
Primarily it's like the screen mapping technique with 100% illumination on, but the advantage is that you have a few basic options such as whether you want to receive objects, and whether you want the object to show up in the alpha channel. A very useful option since otherwise you may create a box as a matte object and have characters walk behind it but when it comes to comping the box will show up in the alpha, not a good thing. Matte/Shadow is the material you'll want to use most of the time since it's designed specically to do one thing and it does it well.
A few final tricks
Screen mapping objects: One feature that can come in handy at times is the fact that screen mapping picks up light as I mentioned. So you can create objects intentionally that don't fit into the enviroment perfectly, such as below I have created some text sitting on the ground using screen mapping. It uses the screens texture but gives it lighting, shadow and depth so it really looks as if it's part of the scene.
This can be handy for some things you may want to do like a crack in the ground, or something coming out of the ground, pillars growing out ect. Who knows, it's up to you.
Mask screen mapping: This is a technique I developed/discovered when I first got into compositing, long before I found out about the camera mapping modifier (which I cover below) which is great technique to put into your tools set. Being able to make a mask for your scene for a specific object, and set it up so that if the object leaves that screen mapped mask it turns into a different texture.
Observe: Below I have created a mask for the pillar plate, which is a mask of the concrete block inbetween the two pillars (available in the pillars.zip file). Now fast forward a bit, I've set up particles to represent the stone block, which I'm going to explode. If you click on the  pillarexplo.avi video, you can watch how it works, although you will notice that the rock once it blows up is still there! Carry on and down the page I'll show you a way around this!
  
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