Re: [Gtk2hs-users] PangoLayout experiences in a DrawingArea

[Duncan C. <dun...@wo...>]

Thanks Brett for the notes.

Sounds like your experience with the crashes etc point to some
ref-counting or other memory management bug in the Pango binding code.

If you still have the code for one of the crashing versions and you
don't mind sending it to us that would be much appreciated.

Duncan

On Wed, 2006-06-21 at 12:35 -0600, Brett Giles wrote:
> Hi All
> 
> I'm sure those of using GTK / Gtk2HS for years will be say - of course! to
> this, for newbies though, I hope it is of some help.
> 
> My situation is that I am working on a project that requires me to draw  a
> multi-branched tree in a DrawingArea. The nodes, leaves and the branches
> are each labelled in a variety of ways, requiring me to position the text
> myself, allow for font changes and allow hiding of certain labels.
> 
> Being new, and happy to experiment, I first started off by just creating a
> PangoContext as I needed it, create/set the font and then create the
> layout, then get the size and draw. (actually, I would usually get the
> size on one pass to compute the size of the whole tree, then again when
> doing the actual drawing.)
> 
> Sadly - not so good. Many crashes in Windows and Linux, many missing
> pieces of text in Windows :).
> 
> Next stage was - well, why not create and save the contexts with the
> correct font descriptions and pass them through the drawing functions.
> Then create a new layout each time from the context
> 
> This seemed to work quite well, other than occasionally the
> getPixelExtents functions would return some very strange values. (e.g.
> Rectancle 0 2999908 20 2999935).
> 
> However Windows barfed quite quickly on this - and was still missing some
> text.
> 
> Finally, I created the layouts once at the beginning of the program and
> pass them around.  Now - all is wonderful, everything displays and nothing
> crashes :). I believe I also need to save the FontDescriptions and pass
> them as well, as everything is still drawn as per the last font context I
> set.
> 
> I'll most likely put this up on the Haskell Wiki this weekend - any
> further comments or thoughts will be gratefully added in there.
> 
> Hope this helps others doing DrawingArea stuff.
> 
> 
> Brett Giles
> Grad Student, Formal Methods UofC
> http://pages.cpsc.ucalgary.ca/~gilesb
> 
> 
> All the advantages of Linux Managed Hosting--Without the Cost and Risk!
> Fully trained technicians. The highest number of Red Hat certifications in
> the hosting industry. Fanatical Support. Click to learn more
> http://sel.as-us.falkag.net/sel?cmd=lnk&kid=107521&bid=248729&dat=121642
> _______________________________________________
> Gtk2hs-users mailing list
> Gtk...@li...
> https://lists.sourceforge.net/lists/listinfo/gtk2hs-users