mac 2,9 "Cannot nest wxDCs on the same window"

[Stefan Csomor]

Hi
> On Mon, 01 Oct 2007 09:55:15 -0700 Robin Dunn <robin at alldunn.com> wrote:
>
> RD> Riccardo Cohen wrote:
> RD> > Hi
> RD> > I have a program that works on wxmac2,7 , but with 2,9 it displays the 
> RD> > following assertion : "Cannot nest wxDCs on the same window"
> RD> > 
> RD> > this happens when I do
> RD> > 
> RD> >   wxClientDC      *dc=new wxClientDC(diag);
> RD> >   dc->DrawRectangle(rec);
> RD> >   delete(dc);
> RD> > 
> RD> > inside a timer_wake event.
> RD> > I do not understand exactly what it means.
> RD> 
> RD> You can not have more than one wxDC active at the same time for the same 
> RD> window.  Somewhere you have another DC already using diag when the code 
> RD> above is called.
>
>  This seems like a rather bad restriction. I wonder if we couldn't make
> all wxClientDC instances on the same window use the same underlying
> CGContext somehow. It could still result in problems with changing DC
> attributes but if we restored them carefully, it would allow something
> (common) like this:
>   
I've tried this in earlier times, but I was not successful when another context for another wxWindow on the same toplevel window that was currently drawing was requested, but since now all code is Quartz only, I could try again.

Neverthelesss I really think that every drawing has to be moved to a OnPaint event, and the only reason to use a dc outside is for measuring purposes, which already can be done. It is the way the new drawing systems perform optimally, intermittent drawing leads to synchronization bottlenecks.

Best,

Stefan