Emit particles from alpha mapped fbx


I have an fbx with an animated alpha map that slowly reveals the object over time. I’d like to emit particles from the edge of the reveal, similar to the logo reveal here:

I can’t seem to figure out how to set it so that particles only emit from the parts of the object that are visible. I tried setting the “pixel cull mode” to alpha channel and playing with the alpha threshold, but no luck. Any ideas? Also if someone could tell me how to make volume shadow shading work with these particles, I would be so grateful.

Here’s the dfx:

You have to link a Light node to the Volume Shadow Shading, for it to work.
Area lights don’t seem to do it, according to the manual.
And make sure to play around with the position of that Light node, move it quite far away from the particles, for it to register, sometimes it is not that accurate.

You might also wanna use a soft gradient as a texture for the particles, as the shading shows better than using the default square points.

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