Graphics

Searching the forums, it looks like this doesn't work but I'm really hoping I just overlooked a solution.

Pretty basic, I want to use a quad to REVEAL another layer, like an alpha mask in After Effects. Let's say I have a 500x500 quad with a video material and I only want to see the middle 100x100 area. I can easily mask that area out with a 100x100 quad with a mask texture, but I need the opposite: the cropped 100x100 center with the outside masked away. I played around with blending options, mix values, layer objects but never got what I needed. And I need to do this multiple times in one scene so I'd like to keep it to two objects per crop if at all possible. Can this be done?

I believe this feature depends on which version of XPression you're on, but in the quad size settings, you can make your quad 100x100 and check the box for maintaining the aspect ration of the material you add to it. In the dropbox below it, there should be an option called cropped that would then do the effect you're trying to achieve.
#XPression

I have had success with mattes on still images but I haven't tried it with video. I build a new material with a single layer. Then I apply the material of the image I want to mask, then I apply a 2nd shader to that layer with my matte.(matte is white with an alpha channel of the shape of my mask) I used this on head shots to fade the bottom edges using a blurred b/w matte. I see no reason why it wouldn't work with video but I've never used it on video I have also made a "reverse mask" that basically looks like a picture frame that is larger than the quad, and the hole is the size I want to reveal. Use it the regular way in a layer object. Good Luck.

#XPression

I think I figured this out a few days ago.

Set the main material's blending to "alpha mask" like you would a normal mask, and then on the video/texture shader set the alpha blending to "use current stage", and boom you've got an alpha mask with optional animation.
#XPression

so many ways to do things
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Thanks for all the suggestions! The maintain/crop solution was the simplest answer for this situation, but I'm keeping the other solutions in my back pocket for other applications..
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