From Xojo Documentation
Draws a rounded rectangle filled with the current color. The current color is set with the DrawingColor property.
x and y are the coordinates of the top-left corner. width and height specify the size of the round rectangle. arcWidth and arcHeight control the shape of the corners in the horizontal and vertical axes, respectively. They are the distance (in points) from the corner at which the arc begins. Setting them to zero results in a rectangle with sharp corners.
g.FillRoundRectangle(10, 10, 100, 60, 30, 30)