On Monday 04 of November 2019, Thorsten Behrens wrote:
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.
I see. That's really non-obvious (and the usual pathetic style of VCL's
documentation doesn't help either), but it kind of makes sense, so I'll make
Skia do the same and add a note to VCL backendtest pointing to this for
whoever will feel like cleaning that mess up somehow.
--
Luboš Luňák
l.lunak@collabora.com
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