Given an array of points, it is easy to draw a line based on these, e.g. using the GraphicsPath class.
For instance, the following array of points...
[0]
This is the function I use to draw a rectangle with rounded corners... from this you may calculate the angle of each line.
Public Sub DrawRoundRect(ByVal g As Graphics, ByVal p As Pen, ByVal x As Single, ByVal y As Single, ByVal width As Single, ByVal height As Single, ByVal radius As Single)
Dim gp As GraphicsPath = New GraphicsPath
gp.AddLine(x + radius, y, x + width - (radius * 2), y)
gp.AddArc(x + width - (radius * 2), y, radius * 2, radius * 2, 270, 90)
gp.AddLine(x + width, y + radius, x + width, y + height - (radius * 2))
gp.AddArc(x + width - (radius * 2), y + height - (radius * 2), radius * 2, radius * 2, 0, 90)
gp.AddLine(x + width - (radius * 2), y + height, x + radius, y + height)
gp.AddArc(x, y + height - (radius * 2), radius * 2, radius * 2, 90, 90)
gp.AddLine(x, y + height - (radius * 2), x, y + radius)
gp.AddArc(x, y, radius * 2, radius * 2, 180, 90)
gp.CloseFigure()
g.DrawPath(p, gp)
gp.Dispose()
End Sub
Hope this help you in the harder part of trigonometry ;)