P3: Somewhat important Description
The BillboardItem3D is currently pretty useless because it can not be scaled or rotated in any way.
I know that the reason for this is that the billboard transformation is applied at the very end of the transformation pipeline, which removes all rotation and scale from the object.
But just a simple example: I'm having a quad and I want it face the camera. But the quad is lying in the xz plane. The camera will never see this quad and I can not change this in any way. Or I am having some particle effects, then I need control of the scale of these particles. It is no use if every particle would have the same size. The only way to alter size and rotation of a mesh used in the BillboardItem3D is in the model editor, before the mesh is loaded and that is pretty inconvenient.
My proposal is to use the pretransform property to apply transformations after the billboard transformation has been applied. Otherwise I think this item should be removed from the API.