Display rendering with cairo (was Re: Rounded corners)

[Hans Breuer <hans breuer org>]

Am 31.05.2008 04:03, Don Blaheta schrieb:
> Quoth Hans Breuer:
> > Am 30.05.2008 09:51, Don Blaheta schrieb:
> > > Yes!  I didn't realise that JOIN_MITER and so forth were already-available
> > > options, but having a single parameter for all objects-with-corners that
> > > said whether to render it as pointy or round would be pretty much what I
> > > was hoping for before I got carried away with the separate radius stuff.
> > But this still does not solve the problem of small radius not being 
> > rendered well with DiaGdkRenderer. And it is not consistent with what other 
> > renderers currently do. I'm using the cairo renderer as my reference here 
> > because cairos main goal is consistent high quality output for different 
> > output devices. See: http://cairographics.org/
>
> I'd seen a lot of reference to Cairo in the code and ChangeLog, and
> gathered that it was the direction Dia was headed (just for export
> formats, or also for realtime display?)---good to read their homepage
> for their goals and perspectives.
Antialised display rendering with cairo is available for a while, too. To 
not confuse it with the Libart antialiased rendering it is best to switch 
off the Libart plug-in. (See very recent ChangeLog entry.)

> But I don't understand your second sentence here: it looks like Cairo
> has exactly this way of breaking down line joins (into mitre, bevel,
> round).  
Setting linejoin and linecaps is part of the renderer interface since the 
beginning, so basically every renderer should be able to do it. The point I 
was trying to make is: Ideally there is no semantical difference when the 
different renderers. For the rounded corner case we still need to find an 
exact definition of what it is supposed to do. If you switch

> In fact, now that I'm looking for it, I see that most objects
> are already using set_linejoin in a lot of places; is it just not
> working?  I guess I just need to explore the code some more.
Especially with the draw_rounded_* and draw_*_with_arrows facilities there 
were (and probably still are) issues due to the piecewise approach these 
methods are implemented. The sample render-test.dia still has a reference 
to it: "was broken by". Also it gets quite renderer specific depending on a 
dedicated renderer implementing some high-level function (e.g. the cairo 
and wnf renderer do for rounded rect) or if it is using the piecewise 
approximation from lib/diarenderer.c. All renderers except xfig do for 
draw_*_with_arrows().

-------- Hans "at" Breuer "dot" Org -----------
Tell me what you need, and I'll tell you how to
get along without it.                -- Dilbert