I am facing the following problem: I have several objects/layers that I want to cast a shadow. Initially, some are hidden behind others but later on I am revealing them, e.g., by sliding them to a new position or fading the layer on top to transparent. Now, when I apply drop shadows to all of the objects those shadows will add up (or rather multiply for the default blend mode) and make the overall shadow darker while the objects are still positioned in the same spot.
What I want, though, is a constant apparent shadow strength, i.e. what you would get when casting the drop shadows onto the background and then combining them by taking the minimum per pixel. I had hoped that the "Darker Color" blend mode would achieve this but it seems to interfere with the opacity of the shadows.
I assume that I could work around this by either using 3D shadows (never used this feature before) or by carefully animating the opacity of hidden objects but I would prefer a more efficient solution. So, is there a way to achieve this differently?