Re: Drawing to screen - nothing appears?

[Steven]

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[I just realized that I replied directly instead of the list - sorry]


I meant as in an instance of the class - but for some odd reason 
neither the OS X nor the Linux gcc gave me even a warning about the 
fact that there appears to be no -lockFocus for NSWindow!  I changed 
the application to use drawRect, and all seems well for now.  I'm using 
- - -display instead of -setNeedsDisplay: because I'm running this in a 
tight loop and it needs to be updated inside of it.  Apparently Cocoa 
is a bit more lenient towards sloppy code ;)

Thanks a bunch!

On Nov 20, 2004, at 4:46 AM, Alexander Malmberg wrote:

> Steven Schlansker wrote:
> > I'm trying to port an application that I've developed on Mac OS X to 
> > GNUStep/Linux and GNUStep/Windows.  I'm currently running Gentoo with
> > gnustep-base/gnustep-base-1.10.2_pre20041116 
> > gnustep-base/gnustep-back-xlib-0.9.5_pre20041116 
> > gnustep-base/gnustep-gui-0.9.5_pre20041116
> > I'm using the libart backend, but xlib doesn't work either.
> > The method I use for drawing goes like this:
> > [NSWindow lockFocus]
> > [NSColor set]
> > NSRectFill (to clear the screen)
> > for()
> >    [NSColor set]
> >    NSRectFill (to draw object)
> > [NSWindow unlockFocus]
> > [NSGraphicsContext flushGraphics]
>
> Out of curiosity, could you provide some "real" example code that 
> shows this? I'm not sure how to read the above pseudo-code (e.g. 
> NSWindow has neither a +lockFocus method nor, if you mean an NSWindow 
> instance, a -lockFocus method, so you should simply get an exception 
> for that).
>
> Anyway, the best way of drawing with -gui (as opposed to using the 
> backend interface directly) is to leave all the focus and gstate 
> handing to NSView and NSWindow and draw from -drawRect:, so if it's at 
> all possible, I strongly recommend doing that. If you need to trigger 
> a redraw at some point, you just call -setNeedsDisplay:.
>
> With other methods, you are (more or less) bypassing -gui's drawing 
> infrastructure, and this is risky and prone to weird behavior. 
> However, in practice, I've had few problems with something like:
>
> (theView is a view that covers the area I want to draw. It probably 
> helps if theView is opaque and has an empty -drawRect:.)
>
> [theView lockFocus];
> /* Draw here. */
> [theView unlockFocus];
> [[theView window] flushWindow];
>
> > Usually nothing shows in the window that I've created.  Sometimes a 
> > rectangle appears as it should, but I can't figure out what triggers 
> > this or why, and it disappears on the next refresh.
>
> Most likely, -gui is going through the normal redraw mechanism in 
> response to something, and various -drawRect:s are drawing the window 
> background on top of your view. They expect your view's -drawRect: to 
> redraw your parts, so the fix is to make sure your -drawRect: does 
> that.
>
> (Using an opaque view should help a bit here since it tells -gui that 
> it doesn't _have_ to clear the window behind your view. It doesn't fix 
> the problem, though; -gui might clear the background anyway.)
>
> - Alexander Malmberg
>
>
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