Stuart:

Stuart:
Attached is another clouds patch. This does the following:
1) Puts the 3D clouds in a cloud rendering bin, to reduce the transparent edge problem. Viewing 3d clouds against a 2D layer _above_ it now blends correctly. There is still a problem when viewing a layer below the 3d clouds, and I'm not sure if/how I'll manage to solve that. Thanks to Tim for pointing me at the correct code (again).
2) Performance improvement by calculating the Bounding box when the cloud is generated rather than ever time it is requested.