PhiziBox is an open-source sandbox physics simulator program (still during development)
and I am sorry you can't change that window size right now but you can edit it from that code but it might also make some bugs
This program is not comlete and there is lots of things that I have to do This program doesn't even have a spawn bodies window(there is one but I am still making it) you can just spawn bodies just by keys on the keyboard now and you can't set their size without editing the code
controls:
press r for a rectangle body
press p for a polygon body(you can edit vertices in the code but it has to be > 2, <= 16)
press c for a circle body(you can change the redies in the code)
press s for small circles(made them just for fun they are really laggy in big numbers)
press n for makeing a new world(resetting the world)
press k for making a kinematic polygon body((you can edit vertices in the code but it has to be >= 3, <= 16)
and you can hold some bodies with mouse left click on the body
you can delete bodies with mouse right click on the body