[Qt-interest] Few questions about drawing text

[Cyril C]

  Le 06/09/2010 08:41, Bo Thorsen a écrit :
> Den 05-09-2010 17:08, Cyril C skrev:
>>   Hi all, I've got simple questions related to text drawing in Qt, for
>> which I can't figure out a proper answer.
>>
>> 1a. Is it legal and portable to draw text in a non-GUI thread onto a
>> QImage using QPainter::drawText? From this nice article by Gunnar (
>> http://labs.trolltech.com/blogs/category/painting ) it seems so, but I
>> am still sceptical..
>
> That should work. QImage is one of the few "gui" classes you can use 
> in other threads, since it's just an internal blob of memory. Be 
> careful when passing it to other threads though.
I think so too but I remember some kind of issue related to a 
text-drawing 3rd party library that may not be reentrant or other 
potential problems...
>
>> 1b. Of course I would prefer drawing to a GLTexture (and not only text)
>> but my understanding is that even in 4.7, drawing to a QGLContexts in
>> separate threads won't be supported, is that right?
>
> That certainly won't work. GL stuff is a hardware thing, not 
> implemented in memory like QImage. AFAIK, you can't even protect all 
> GL access with mutexes (which would anyway completely ruin the idea of 
> threads).
Well officially , OpenGL *is* reentrant but last time I checked (more 
than 1yr ago), *QtOpenGL* is not. If it was, we could use a different 
GLContext in each worker thread, as long as they don't access the same 
objects (FBOs, textures..) at the same time.


Does someone know about my last question ?
2. Does QGraphicsTextItem or QGraphicsSimpleTextItem take advantage of 
QStaticText? I am under the impression that it's not the case, even 
though graphics text items are pretty static in most use cases.

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