Compiling using
/ $ cd godot-cpp/
/godot-cpp/ $ scons platform=linux
/godot-cpp/ $ cd ../
/ $ scons platfor=linux
I used an Area as the holder of the script that had a mesh and a Collision Shape object. The circle class used the area_entered signal to notify the circle when it collides with either the wall or another ball. When this happens it then gets the walls normal and uses Vector3:Bounce to calculate the reflected vector.
Link here here