Objects: Support for n-gons

[izzylys]

Support n-gons or triangulation of them in mesh conversions on receive using the n as the first item in the polygon index array.

Once we have more complete support across connectors, we can consider using 3/4 indicators for outgoing faces in ToSpeckle conversion. Currently, we are still using 0 and 1 for backwards/cross compatibility.

Support for 3/4 faces

• [X] Revit
• [x] Viewer - see https://github.com/specklesystems/speckle-server/pull/486
• [x] Rhino
• [x] Blender
• [x] Unreal
• [x] Unity
• [x] Sketchup
• [x] AutoCad/Civil3D
• [x] Bentley

Support n-gon ToNative conversion

• [x] Revit - see https://github.com/specklesystems/speckle-sharp/pull/831
• [x] Viewer - see https://github.com/specklesystems/speckle-server/pull/508
• [x] Rhino - see https://github.com/specklesystems/speckle-sharp/pull/818
• [x] Blender - see https://github.com/specklesystems/speckle-blender/pull/66
• [x] Unreal - see https://github.com/specklesystems/speckle-unreal/pull/24
• [x] Unity - see https://github.com/specklesystems/speckle-unity/pull/55
• [x] Sketchup
• [x] AutoCad/Civil3D - see https://github.com/specklesystems/speckle-sharp/pull/949
• [x] Bentley - see https://github.com/specklesystems/speckle-sharp/pull/1082

Documentation

• [ ] Document n-gon support across connectors, and detail limitations/lossy conversions.

[JR-Morgan]

The Viewer, Unity, and AutoCad don't support N-gons/face triangulation natively, and so we would have to triangulate them during ToNative conversion.

I propose creating a triangulation function to be added to the Objects namespace. Then the AutoCad and Unity connectors can both use this function. This function (or a similar one) can be created in JS to be used by the viewer.

Ideally, this function should be able to deal with concave and non-planar faces.