Nuke Expression Question

[user_deleted]

Hi!

I got a question concerning a specific 3D compositing issue I want to solve with Nuke expressions.

I created an atmospheric fog effect using several fog layers spread in the whole 3D space. The camera moves slightly through the fog and I want to create a fade-out effect when the camera gets close to a fog layer. So I need to retrieve the current 3D position of any fog layer in order to create that depth-fade effect. So how do I get the current position of a layer without linking the position channels from the downflow TransformGeo node? Something like "getAttr(pos.x)" or anything like that.

Thanks a lot!

Phong

[user_deleted]

I might be wrong but I don't think you can access the transformation matrix like that. You'll have to use node knobs.
I would probably just use the depth channel that comes out of the render node since it hold more accurate information per pixel anyway than reading out a cards distance to camera which only gives you the proper information about the cards center in relation to the camera.

would that be feasible in your situation?

cheers,
frank

[user_deleted]

Hey Frank!

Thanks a lot for your reply. I actually intended to use the depth channel, but since the fog consists of a lot of layers with alpha, the z channel pixel value is not explicitly related to a single card anymore.
Would be great if you had another idea.

Thanks!

Phong

[user_deleted]

maybe you could cheat it by using the card's distance to the camera to feed into a fade node for your texture before it goes into the card. but that would require linking to the respective TransformGeo nodes which you're trying to avoid.