yes, you can, i'm not pro on otclient sources and can't help you on how to do it but:
the square is a sqm delimiter of a 32x32 pixel.. if you want a circle you will have an tangent circle of the 32x32 square.. and for all other geo forms you'll act like this.. get the square function and use a simple math transform to make it a circle, hexagon or whatever form you need..
remembering, if you need a circle drawing you'll use a circle with 16 pixels of radius..
hoping to help..
if you find the drawing function i'll try to code it, if you can't...