From Xojo Documentation
Used for drawing arcs in a vector graphics environment.
A StartAngle of 0 means due east, i.e., a positive X value with Y = 0. Positive angles are clockwise, just as with Object2D rotation. The value of ArcAngle can be positive or negative, extending from the starting angle. If the angle is filled, it produces a wedge; this may be useful for making pie charts, for example.
The radius of the arc is determined by its Width and Height properties. These are inherited from RectShape. The default values of Width and Height are 100 pixels. This means that the default value of the radius is 100/2 = 50 pixels.
a.ArcAngle = 1.57
a.StartAngle = -1.57
a.FillColor = RGB(255, 0, 127)
g.DrawObject(a, 100, 100)