The error here is that when forward referencing a struct/class what matters is whether the entity actually is a struct or a class. For example, this is what the definitions look like if the entity is:
a class: ?Init@SimpleDrawable@Scene@OpenVulkano@@QEAAXPEAVShader@23@PEAVGeometry@23@PEAVMaterial@23@@Z
a struct: ?Init@SimpleDrawable@Scene@OpenVulkano@@QEAAXPEAVShader@23@PEAVGeometry@23@PEAUMaterial@23@@Z
