Thanks for your quick reply! :)
Ahhh, I see. Performance wise, is it an issue to create a group per sprite shadow/object to have individual depth values per shadow?
Can we access the buffer/surface the sprite shadows are drawn on and render them individually?
Also, ist it possible to find out whether and where an object is collides with a (sprite) shadow? This would be interesting because - if there is access to the sprite shadow buffer(s) - the shadow could be distorted by other objects behind the one that casts the shadow to mimic a more three dimensional shadow.
Vertex shaders look really cool, but they act more like occluders, right? Or are the mesh shadows able to cast shadows similar to sprite shadows where there is a certain shape to them?