use a map.
The actual button would be square or rect, when clicking on it, check the x,y coord, compare it with a map (for example an image of a white filled circle on a black background), if the result of the comparison is white, then you clicked on the circle.
The actual button would be square or rect, when clicking on it, check the x,y coord, compare it with a map (for example an image of a white filled circle on a black background), if the result of the comparison is white, then you clicked on the circle.