radius property
The radius of the circle which defines the inner rounding arc of the corner.
A value of 0 indicates that the corner is sharp, or completely unrounded. A positive value is the requested size of the radius.
This is an absolute size that should relate to the overall size of the shape. If the shape is in screen coordinates, the radius should be sized accordingly; if the shape is in a canonical form, such as the bounds of (-1, -1) to (1, 1) that RoundedPolygon.new produces by default, the radius should be relative to that size. The radius is scaled when the shape itself is transformed, since it produces curves which round the corner and so are transformed along with the overall shape.
Must be greater than or equal to zero.