Creating a look through mask

Hi guys,

I’ve been looking for a way to do this for a while but keep drawing blanks so thought I’d try the forums. Hope I can explain this well enough! I want to create a portal effect very cheaply for use in VR. Because it’s stereo VR the “render to texture” option is too expensive so what I’m hoping for is something along the following lines.

I have a sphere with the normals flipped and a space texture applied so you can look in to it and see stars etc. I want to put a planar piece of geometry in front of this so that only the parts of the sphere seen through this are actually visible. so the effect is like looking through a door in to space. The sphere must only be visible through the planar “Door” so that if you walk around the door there’s nothing behind it!

I’ve tried the Sphere Mask approach but this relies on the sphere intersecting with the mesh where as I need a look through mask effect. The player pawn will never actually enter the portal but NPC’s will get pulled in to it (and disappear with it).

Any ideas on this? any help would be very, very welcomed!



46 View and no answers… So this is impossible?

Not sure if I understand, but correct material with radial mask should do the job? I don’t see problem there. Also you can hide the world entering inperfection for NPCs with some particle effects. Bellow link for more advanced approach…


Example of effect

Thanks for that, Sorry if I seem a bit thick but I come from an animation background so doing this in realtime is completely different to how I’d do it in Maya, after Effects etc…
The radial mask would reveal parts of the mesh but would be a texture applied to the mesh. What I need is a mask applied to one piece of geometry that reveals only the parts of a second piece of geometry, the parts that are seen through the first piece of geometry…

See the example below which I hope makes things clear…

Thanks for any help you can give with this guys… The Epic Forum and community are fantastic for those of us taking our first steps in to realtime 3D!

The sphere is not needed. All you need is a plane with a cubemap using the cameravector as UVW input.

So the texture is offset in relation to the camera position giving the illusion of depth? You sir are a bloody legend! thank you!
(Sorry I described the goal so poorly at the start as well)!

Thanks again


Look at how to author and apply cubemaps, rest should be easy as pie.