Re: drawing to NSImage off display

[Scott Christley]

Hello Fred,

I've filed bug # 26535 for this issue and attached a test app  
illustrating the problems.  There is an issue with threads as the app  
illustrates but there is also an issue with scaling.

https://savannah.gnu.org/bugs/?func=detailitem&item_id=26535

thanks
Scott


On May 11, 2009, at 12:14 PM, Scott Christley wrote:

> Hello Fred,
>
> I think I'm mistaken about it working before, well my program was  
> working before but the drawing code was architected differently.  I  
> coded it to be more efficient, but this was done on Mac.  I thought  
> that it worked with the stock GNUstep that you get on Debian, but I  
> tried that over the weekend and no go, that actually crashes when it  
> tries to draw in the NSImage.  So I don't think I ever got the new  
> code working with GNUstep yet.
>
> Anyways, I did discover a few things.  There seems to be a  
> combination of issues.
>
> * It is *not* an issue with images loaded from files; those seem to  
> work fine in all cases, so it seems to be primarily related to  
> allocated images that you then attempt to draw within and then  
> display.
>
> * Scaling is not working for allocated images.  However if I don't  
> scale the image, then I can get it to display (under the right  
> conditions).
>
> * Doesn't seem to be an issue with threads.  Have the same problem  
> both in the main and secondary threads, though this is confounded by  
> the next issue.
>
> * A key issue is that drawing into the image does not appear to work  
> unless I do it within the context of NSView's -drawRect: method.  So  
> if I draw into the image in a target-action method (say) from a  
> button click, then try to compose that image into a view, it doesn't  
> work.  If I draw into the image during drawRect: then it appears to  
> work, but I have the scaling issue mentioned above when composing.
>
>
> I will work on a constructing a small test application that shows  
> these different combinations.
>
> cheers
> Scott
>
>
> On May 9, 2009, at 7:38 AM, Fred Kiefer wrote:
>
> > Hi Scott,
> >
> > when you are saying that it worked before, at what time was that? A  
> > few days ago, weeks, months? As far as I know, drawing in a  
> > separate thread should have produced an error up until two months  
> > ago.
> >
> > Is your code working when executed in the main thread? If not we  
> > should try to get it working there first.
> >
> > Is there already anything in that image you are drawing on?
> >
> > It would be helpful if you could send full working code to  
> > reproduce the problem, then sonebody could look at your code  
> > directly and also test whether it works on his machine. That  
> > somebody couldn't be me at the moment, as I am travelling, but as  
> > soon as I am back I would test your code.
> >
> > Fred
> >
> > PS: There was a similar bug report some time ago, but this is fixd  
> > and closed now. Perhaps you could have a look at that.
> >
> > -------- Original-Nachricht --------
> > > Datum: Fri, 08 May 2009 18:45:00 -0700
> > > Von: Scott Christley <schristley@mac.com>
> > > An: gnustep <discuss-gnustep@gnu.org>
> > > Betreff: drawing to NSImage off display
> >
> > > Hello,
> > >
> > > Some code which use to work is no longer working and I'm not sure  
> > > why.
> > >
> > > I use some worker threads to do computation, then they draw into  
> > > their
> > > own personal NSImage objects, which are then passed over to the main
> > > GUI thread to be displayed.  It seems that the drawing into the
> > > NSImage is not working properly.  The method for each worker thread
> > > looks somewhat like this:
> > >
> > >
> > > - doWork
> > > {
> > >         // do some stuff
> > >
> > >         [image lockFocus];
> > >
> > >         [[NSColor greenColor] set];
> > >         NSRectFill(aRect);
> > >
> > >         // do some more drawing
> > >
> > >         [image unlockFocus];
> > > }
> > >
> > >
> > > Is there any reason why drawing into NSImage, either off display  
> > > or in
> > > worker threads, should not work?
> > >
> > > I verified that nothing is wrong with the rest of my code, because I
> > > can change that -doWork method to just load an image from a file,  
> > > like
> > > this, and the image displays just fine:
> > >
> > > image = [[NSImage alloc] initWithContentsOfFile: file];
> > >
> > >
> > > On a secondary note, I tried saving the image to a file, after I -
> > > unlockFocus, but it produces a corrupt file.
> > >
> > > [[image TIFFRepresentation] writeToFile: file atomically: NO];
> > >
> > >
> > > I'm using GNUstep from SVN, on Debian with the art backend.
> > >
> > > thanks
> > > Scott
> > >
> > >
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> >
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