[cairo] line width questions

[Behdad Esfahbod]

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.


behdad