User-defined clipping planes

For example, to reveal the interior of a CAD model in a 3D tileset.

Support up to 6 planes so a user can create a cube.

The classic implementation of this is a fragment shader with a 1D alpha texture (or maybe just discard).

Probably expose this for 3D tilesets and glTF models. We can add it to primitives, terrain, etc. if those cases come up.

[nmschulte]

I’m not sure what you mean by having the planes themselves be “shaded”, if you could provide an image similar to what you mean that would be helpful.

After playing with this some more I can clarify now. I’m focusing on clipping the globe, for subterranean concepts, but the idea should generalize. What I had in mind is this: – Where the clipping planes intersect the geometry/mesh, shade the intersection face(s). E.g. when clipping the globe to slice it in half, allow to shade (with a full blown material/shader, or a simpler interface like ARGB color) the resulting ellipse of the intersection.

Bigger picture: I want to provide a better back-drop for entities/primitives/meshes placed inside the clipped region of the globe. If this was done with actual geometry/mesh, this could improve the current default camera behavior too (as it is, it seems one can “pick” a point “inside” the globe as the camera manipulation ref. pt., see the attached animations).

I also want to show the original clipped surface with a different shading (material/shader), much like this “other idea”:

Implement as a material? This would allow modifying the color of the clipped area or just do regular discard.

More than six planes may be handy for more complex geometry carving; the ability to specify an arbitrary geometry would be amazing, but that might be out of scope given the tech in focus here.

Last, if it matters, the ability to clip entities/primitives would be neat. I don’t have a concrete grasp on the technical limitations though; I haven’t yet dug into how this is implemented.

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[lilleyse]

clip-planes-master branch is ready.