Feature request: Connected outlines for flat-shaded faces

[mattrossman]

When loading a model with flat-shaded faces, outlines appear disjoint:

This matches the behavior in UniVRM and the Blender VRM add-on, however it's not always desirable for artists.

Blender's glTF exporter (and perhaps other exporters?) exports flat-shaded geometry with non-shared vertices. For example, exporting the default cube (8 vertices) yields a glTF model with 24 vertex position vectors. I'm not sure the exact reason, but I assume it's so that it can include normals data for these verts to ensure they appear flat in other renderers.

I would like the VRM loader to have an option to intelligently recalculate normals for the outline geometry so that these overlapping vertices appear connected.

I think this can be achieved with the help of THREE.BufferGeometryUtils.mergeVertices() and THREE.BufferGeometry.calculate.vertexNormals() inside the VRM loader, and perhaps tweaking the outline shader logic.

[0b5vr]

The behavior is not well-defined on the spec side, and if we try to strictly define the spec this is going to be a spec as-is.
Until we define a platform-independent way to achieve smoother outlines for these cases, you probably should resolve these cases by model side (e.g. inserting a small bevel 😩).