wgsl ShadowOnlyMaterial

[ryantrem]

Shaders in @babylonjs/materials have not been ported to wgsl. For the Viewer, we now have a dependency on ShadowOnlyMaterial, so it would be good to at least port this one to wgsl for a better Viewer experience.

[sebavan]

Wondering if we could use backgroundMaterial in the viewer for this and maybe the skybox ?

[deltakosh]

Agreed. @ryantrem why using shadowOnly instead of backgroundMaterial?

[deltakosh]

Closing as unneeded for now