Wireframe stencil(?) - terrain editing tool radius in UnrealEd

[halo]

Here's what I want:
http://udn.epicgames.com/Two/EditingTerrainMaps/painting3.jpg

It's a circular wireframe that lies along the terrain as you move the mouse. I could calculate the line intersections myself and build a mesh on-the-fly, but it would be slow as hell. Is there a way to render this?

[mikael_aronsson]

If you want OpenGL to do the hard work you could use the GLU nurb surface tesselator to generate to mesh for you.

Mikael

[Omaha]

Seems to me you could establish the mouse position projected down onto the map, and then while rendering the map render a second pass at that part with the same geometry but no depth writing, some z offset, and an additive/blend/whatever texture.

[halo]

I'll look into the nurbs thing.

I don't want a blended texture, I want a wireframe circle.