Re: [Plplot-general] Polygons get clipped by removing the vertices

[Maurice L. <mj...@ga...>]

Arjen Markus writes:
 > I have built a small function to plot (filled) circles via polygons and 
 > I have noticed that the polygons are clipped by removing vertices that
 > fall
 > outside the viewport. The consequence is that large circles are no
 > longer 
 > recognisable as circles. 
 > 
 > Is there a way out of this? The polygons should - in my opinion - be
 > drawn from all the vertices and the clipping should occur on the polygon
 > as a whole.

Polygon clipping is fairly complex.  The issue really raised its head when I
implemented zooming in the plplot TK interface and started doing a lot of
shade plotting, way back in '94 or so.  I worked on it for a while before
giving up due to lack of progress even though there were still a lot of
problems with it.  As an example, run "x16c -dev tk", zoom in on a section and
then pan around.

Anyway I decided to take another look at the code and noticed right away
problems with the existing approach.  Emboldened, I set about to improve it
and now am happy to say it works much better than before.  Grab the latest
src/plline.c from cvs HEAD and see if the new code fixes your problem.

Note it still does not work perfectly -- at a sufficiently high level of
zooming we start to get clipping problems again.  These I suspect are due to a
fidelity problem, either in clipline() or somewhere else.  Anyway no more time
to work on it for now.

-- 
Maurice LeBrun
Lightspeed Semiconductor Corp