Java2D best way to pick various image with Alpha background overlapped?

Question

I am developing an isometric game in Java2D. I.e, note that I do not have direct access to hardware pixel shaders (real-time software pixel shaders aren't practical. I can do a single pass on every entity texture without a noticeable hit on performance)

I know the typical method would be to somehow encode the depth of the individual pixels into a depth buffer and look that up. However, I don't know how I can do that efficiently in Java2D. How would I store the depth buffer? How would I filter out the alpha in an image? Etc.

Up until now I have just been reversing the projection matrix I use to calculate the tile-coordinates. However, that doesn't work well when you have entities that render outside of those tile's bounds.

Another method I considered was using a color-map, however I have the same problems with this as I do with the depth buffer (and if I can get the depth buffer working I'd much rather use that.)

Here is a picture of what I am working with:

Answer 1

I've resolved this quite nicely. The solution is actually very simple, just unconventional.

The graphics are depth sorted via a TreeMap, and then rendered to the screen. One can simply traverse this TreeMap in reverse (and keep it until the next render cycle) to translate the cursor location to the proper image it falls over (by testing the pixels [in reverse render order] and checking if they are transparent.)

The solution is in the open-source project, under the io.github.jevaengine.world.World class, pick method. https://github.com/JeremyWildsmith/JevaEngine/blob/master/jevaengine/src/main/java/io/github/jevaengine/world/World.java