I've done this in stellarium to some degree but i am still not very happy with it because I still can't quite get an accurate estimate without a tremendous amount of manual work, so someone actually actively working on this would be amazing.
A widget version would be nice!
As I said in another comment, a true killer feature would be to image my yard, with all the obstacles blocking the sky, and intersecting the available sky space with the trajectories of those objects, and use that info to actually tell me what I can image.
Instead, you should just figure out what the degrees of the top of your blocking items are and set that as a limit. If the tops of trees mean something needs to be at least 30° above the horizon, then use that value. If your neighbor's house means it needs to be 60°, then use that value. Being allowed to say 30° to the east, 60° to the west, etc would be even better. Imaging your yard and having to decipher all of that would be way overkill and totally unnecessary.