Arbitrary texture mapping (Patreon)

The current version of SpaceSim can add a texture which is mapped to the surface of a sphere. This works well for sphere-like objects, but creates visible distortions when the shape is significantly different from the sphere.

I'm adding additional options for texture mapping, including support for texturing coordinates loaded from user-provided mesh objects, such as .obj or .gltf files. This way, it's possible to load not just the shape but also the materials from the mesh files.