I'm trying to use GP:DRAW-ARC to render pie charts. I must be
misunderstanding something because I'm not getting the output I was
expecting. This code
(let ((x (contain (make-instance 'output-pane))))
(gp:draw-arc x 0 0 130 130 0 (* 0.5 PI) :filled t))
generates the attached screenshot. I was expecting to see a filled-
in quarter of a circle. Am I misunderstanding what draw-arc is for?
Bill
I think that most draw-arc behaves the way you expect. Try
(let ((x (capi:contain (make-instance 'capi:output-pane))))
(gp:draw-arc x 0 0 130 130 0 (* 1.5 PI) :filled nil))
for instance. I imagine that what you'r'e expecting. It looks like what
is happening is that the *filling* isn't what you'd expect. for instance
(let ((x (capi:contain (make-instance 'capi:output-pane))))
(gp:draw-arc x 0 0 100 100 0 (* 1.5 PI) :filled t)
(gp:draw-arc x 100 100 100 100 0 (* 1.5 PI) :filled nil))
gives the results in the image i've attached. It seems like the arc is being
drawn as a polygon and so the filled region is that inside the polygon
when the two endpoints of the drawn arc are joined. I would have thought
(and I'm guessing this is what you expected) that there might be an extra
vertex at the center of the (implicit) ellipse.
On 10/23/06, Bill Atkins <atkinw@rpi.edu> wrote:
> I'm trying to use GP:DRAW-ARC to render pie charts. I must be
> misunderstanding something because I'm not getting the output I was
> expecting. This code
>
> (let ((x (contain (make-instance 'output-pane))))
> (gp:draw-arc x 0 0 130 130 0 (* 0.5 PI) :filled t))
>
> generates the attached screenshot. I was expecting to see a filled-
> in quarter of a circle. Am I misunderstanding what draw-arc is for?
>
> Bill
>
>
>
>
>
>
>
--
=====================
Joshua Taylor
tayloj@rpi.edu