incorrect line rendering

[Keith Packard]

On Mon, 2007-10-15 at 15:04 +0200, Matthias Hopf wrote:
> On Oct 14, 07 06:51:52 -0500, Pat Kane wrote:
> > On 10/13/07, Marco <marcodefreitas at gmail.com> wrote:
> >   > I have noticed that arcs and lines in certain angles are rendered
> > ugly in X11.
> > 
> > Attached is a little Xlib program that draws both 0  and 1 width
> > lines.  The 0 width lines look much better on my box with
> > xorg-x11-server 1.3.0.0-22.fc8  and I810 driver.
> > Some of the width 1 lines look very  ugly.
> 
> Unfortunately, >0 width lines are exactly specified in X, and the
> specification is actually broken (WRT quality of lines). We cannot
> change the implementation, because that would violate the specs.

Indeed. There is a long and sordid story about wide lines in X,
involving the original PostScript spec (from which the X spec was
derived, but which no PostScript implementation actually follows), a PhD
student (John Hobby) at Stanford (whose thesis advisor, Lyle Ramshaw,
worked at Digital, along with many of the X11 developers and designers)
and the thesis itself which solves all of these issues nicely (using a
polygonal pen of just the right shape instead of a circular pen).

Just accept that core X has really bad wide primitives and move along to
using a more sensible drawing library, like cairo, which doesn't use any
of the core primitives, and has the ability to drive X, OS X, Windows,
PS and PDF from the same API (which takes the beautiful API design of
PostScript and throws away the dire pixelization rules).

-- 
keith.packard at intel.com
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