I can't get the Alpha Matte to work

[serendipidousman]

I am trying to use a shape layer to create a matte to reveal a photo underneath a 3D image,  It is a simply wipe transition that isn't working for me. The two layers I am working with aren't 3D images, one is a purple layer with a texture and the other is a shape layer that I am moving to be revealed by the 3D "50". I have the picture layer above my shape layer, but every time I change the shape layer to "Alpha Matte" the whole screen goes blank. Refer to the video. Any help would be very much appreciated.

https://youtu.be/rRZHyrCY108

[Mike_Abbott · Accepted solution]

TBH I'm finding your description a little difficult to follow - but there are a few important things to know that should solve your problem:

1. It looks like your Composition is set to operate with the Cinema 4D renderer. See: Composition > Composition settings > 3D renderer tab. Track mattes are not supported by this renderer.

To work around this: take your 3D layer - I guess your 50 Text layer - with any camera and lights, and pre-compose them. Then make the downstream comp a 'Classic 3D' composition. You can then make your track matte in this downstream Comp.

2. The 'cutter' of the track matte assembly needs to be the top layer of the two.  You select the matte using the TrkMat menu on the layer immediately below.

[Rick Gerard]

It is nearly impossible to see what is going on in your comp. It's probably nothing more than a workflow issue. Post a screenshot with the modified properties of the layers giving you problems revealed (press uu) and make sure we know what layers are what and we should be able to help you. Don't crop the screenshot.