Three.js: Geometry without faces is still rendered in Mesh

[makc]

The idea is that my Geometry always has same vertices, but faces are added optionally. However, it randomly decides to draw stuff regardless. Demo here.

[makc]

An opposite issue here - we don't see faces where they are defined. So maybe this is because Geometry is shared between the Line and Mesh.

[Mugen87]

I've debugged this issue today. Geometry is internally converted to BufferGeometry. The outcome of this conversion depends on the type of object (Mesh, Line, etc.). So in @makc's example, the geometry is converted as the geometry of a Line object. This will create a position and color attribute. When the instance of Mesh is rendered with the same Geometry object, the renderer returns the same cached instance of BufferGeometry.

https://github.com/mrdoob/three.js/blob/ec67749b0767e2727deebd52da2dbd3a4e7ab6a2/src/renderers/webgl/WebGLGeometries.js#L63-L65

This is the reason why you see these green triangles in the demo. Mesh and Line share the same internal BufferGeometry and interpret it differently. I think we can solve this problem if we try to respect the type of object when caching the BufferGeometry.

Or we just recommend to use BufferGeometry in the first place :sweat_smile:

[Mugen87]

@mrdoob I suggest to introduce a new label Wont't fix, assign it to the issue and close it. I don't think it makes sense to add a fix to the renderer if the project is going to stop rendering Geometry anyway. The solution for this issue is the usage of BufferGeometry.