VCL drawPolygon() off-by-one without line color

Thorsten Behrens thb at
Mon Nov 4 16:34:21 UTC 2019

(re-sent due to odd fdo bounces)

Hey Luboš,

Luboš Luňák wrote:
> Is this some kind of a strange rule that I'm not aware of? Does
> somebody know a good reason why all graphics libraries would do
> this?
Yes, essentially all graphics systems fill polygons like that
(including 3D ones). The reason is that otherwise you cannot render
pixel-perfect adjacent polygons without occasional overlap (especially
for non-straight connecting lines).

So really drawRect() is the odd one out, as Caolan suggested.

...and now you know why the code is so littered with this +1/-1
corrections for rectangles. The (now gone) software renderer in
basebmp had some comments about those subtleties, and some explicit
adjustments in the svp backend layer above.


-- Thorsten
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