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

[Riccardo Cohen]

Actually I found an unnecessary wxClientDC creation, I removed it and 
all went all right. I changed my code to call some RefreshRect() instead 
of  drawing directly...
thanks


Riccardo Cohen wrote:
> I agree and admit that it is the safiest way, but it is often easyer to 
> do a "draw now" under certain user action, rather than "change data" 
> then "refresh"...
> 
> For instance when a user select a zone, I have a mouse motion event, and 
> I want to draw a rectangle that follows the mouse to show the zone, I 
> can resize a rectangle object and then refresh, but it is easyer to call 
> drawrectangle() immediatly. The same for timer event : for blinking 
> objects I simpy change the color at each timer event and draw a little 
> point with this color.
> 
> My present problem is that I used this method quite often. Buf if quartz 
> does not allow it, I'll change my code.
> 
> By the way you spoke about measuring, it happens that in the destructor 
> of one of my windows, I have call some cleaning code that create a DC to 
> measure text size. This lead to an exception while in the window 
> destructor. Maybe you've got an idea for that point also.
> 
> 
> Thanks for your great work anyway.
> 
> Stefan Csomor wrote:
>> 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
>>
>>
>>
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> 

-- 
Très cordialement,

Riccardo Cohen
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