[Lazarus] IDE Editor incredibly slow on newer GTK2

Bernd Kreuss prof7bit at googlemail.com
Sat Mar 24 21:02:39 CET 2012

I recently updated my ancient Ubuntu Hardy to Oneiric which has
GTK-2.24.6. Now I noticed that the SynEdit in the Lazarus IDE feels
painfully sluggish. If I press a key there is a 0.2 seconds delay until
it updates the screen. If I keep the key pressed (auto-repeat) then xorg
will burn 60% and kernel (IO or something) the remaining 40% of my CPU.
It gets worse the bigger the editor window is (maximize window for
maximum pain).

Although one could argue that a Pentium-M (1 core at 1.3GHz) is not the
fastest CPU I am not yet willing to throw away my good old thinkpad T40
which has served me so well for such a long time.

It does not happen if I use the Qt widgetset (but I rather do not want
to use Qt but if this can't be fixed then I will have to, otherwise it
is completely unusable, currently it feels like I'm sitting in front a
66MHz 386 from 1990).

I can NOT reproduce it if I create a minimal application with a synedit
and Pascal highlighter on it. I'm unable to reproduce this, no matter
what options I set in my synedit or what highlighter I use and on the
other hand I cannot find any editor option in the IDE to disable to make
it run as fast as the synedit in my own application. I also went back a
few thousand SVN Revisions until I could not compile with fpc2.6 anymore
but could not find any revision that wont have (or trigger) this bug.

The IDE seems to do something with the synedit that (judging from the
massive xorg and kernel usage and the dependency on the window size)
must have something to do with the rendering of the control. And it also
seems to do this only in certain GTK2 versions and not in Qt. What could
it be? Where should I start looking for the cause of this?


PS: I have no problems with any other GTK2 Application, no problems with
slow rendering. Accelerated rendering/compositing is working, Firefox,
Flash-Videos, OpenGL-Applications, everything working exactly as good
(and some things even better) as in my old Hardy install. Only the
Lazarus source editor has become slower by a factor of 20 at least.
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