Hide area of an SCNMaterial

Question

I'm using SceneKit and ARKit 1.5, once a surface has been mapped I apply a material to it.

I would like to only show what's under the camera in a certain radius with an alpha effect. I want to keep the material static meaning that it does not move when the camera moves, only the radius shape will move.

What kind of technique could I use for this ?

ArCore by Google does this perfectly.

Actual rendering:

Desired Rendering:

ARCore example: (click to see GIF)

Thank you!

Answer 1

I would use a shader modifier to achieve that.

Using the .surface entry point you could set _surface.transparent to a value that depends on the distance between the shaded point and the point of view:

_surface.transparent = attenuation(length(_surface.position));