Re: How wide can a widget get ?

[Paul Pogonyshev <pogonyshev gmx net>]

John Cupitt wrote:
> On Thu, 9 Dec 2004 03:58:37 +0200, Paul Pogonyshev <pogonyshev gmx net> wrote:
> > > > What's the maximum width I can set a widget to ? I end up attempting
> > > > to set the width of one of my drawing area widgets to 66327, and it
> > > > doesn't seem to want to go that wide. Is there an inherent limit to
> > > > the width of a widget ?
> > >
> > > There was in gtk+-1.2, but gtk2 (pretty much) removed this. I have
> > > drawing areas in my app which go up to several million pixels in each
> > > axis and gtk scrolls them fine. Memory isn't allocated for invisible
> > > pixels, so there's no limit there either.
> > >
> > > You can have problems with a 16 bit coordinate limit on drawing
> > > operations on very large drawing areas: you may need to do some
> > > clipping yourself.
> >
> > Can you please explain this further?  (Sample code would be especially
> > helpful.)  Here is one particular example that causes problems:
> >
> >         gdk_draw_line (window, gc, 20, 20, 20, 40000);
> >
> > Instead of going downwards, the line goes upwards (seems like X
> > considers 40000 to be a negative 16-bit number.)
>
> Yes, you've hit the 16 bit coordinate limit (+/- 32k). This will
> limitation will vanish at some point in the beautiful cairo future (I
> think), but it's very annoying until then.
>
> The solution is to do some clipping yourself before issuing the draw
> command. You know the position and size of the viewport, so you need
> to draw just the bit of the line that intersects that area.
>
> AFAIK, the 16 bit limit is for the length of the line rather than the
> absolute position (thanks to the magic of gdk2 scrolling), so
>
>     gdk_draw_line (window, gc, 20, 35000, 20, 40000);
>
> should work ok (provided your viewport is positioned at 35000 or lower).

It seems that you are right.  At least after I implemented clipping which
limited line length to be not much larger than view port's width/height,
all drawing glitches seem to have disappeared, even in the "sign flip
zone."

Thanks for the help!

Paul