and 3D CPU particles. The new emitter is called "ring"
and it can emit either in a ring or cylinder fashion.
This adds the following properties for the emitter:
1. emission_ring_axis: the axis along which the ring/cylinder
will be constructed
2. emission_ring_radius: outer radius of the ring/cylinder
3. emission_ring_inner_radius: inner radius of the cylinder.
when set to zero, particles will emit in the full volume.
4. emission_ring_height: height of the ring/cylinder emitter.
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