[cairo] line width questions
behdad at behdad.org
Mon Aug 18 16:00:05 PDT 2008
Bill Spitzak wrote:
> Also OpenGL, Windows GDI, GDI+, PDF, AGG, SVG, DirectX, SilverLight, and
> a whole lot of others use "zero line width" to mean a special line
> drawing algorithim. In fact it has been in *every single graphics api* I
> have ever seen that has an ability to set the line width, except for Cairo.
> I have said this quite a few times on this mailing list but there seems
> to be no interest in replicating it in Cairo, and have pretty much given
> up as I don't want to make myself too much of an a**hole about it.
There's just not been a decent API for this proposed (abusing 0 is a
non-starter). After it's proposed and discussed, a patch is welcome.
> The best definition of zero line width is that you get the smallest
> integer number of device pixels that is larger than a fixed distance,
> such as 1/300 of an inch (this would match what PostScript did on the
> first printers that used it).
So what does it get you for on-screen? 1px wide? What about when we get
350dpi displays? We already see 280dpi ones.
> In addition the line ends are adjusted so that horizontal and vertical
> lines are aligned with pixel boundaries so that the line thickness looks
> the same no matter where it is drawn.
This is where it becomes impossible to implement. No matter which side you
round, it's going to make someone unhappy.
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