Re: Changes to graphic context handling

[Mark Tracy]

Fred,
The change you made has broken one of my programs. I am printing from  
a windowless custom view because I want to lay out the report for  
paper not the screen. Maybe not a wise strategy, but certainly not an  
illegal one. This works fine for Cocoa and for previous editions of  
GNUstep.

In  svn 24892, NSView.m line 1900, there is:
- (void) lockFocusInRect: (NSRect)rect
{
    [self _lockFocusInContext: [_window graphicsContext] inRrect: rect]
}

In my program, since the view is not associated with a window, nil is  
passed, and I get a segfault trying to read the context.

I changed it to read:
- (void) lockFocusInRect: (NSRect)rect
{
    NSGraphicsContext *ctxt =
      (_window ? [_window graphicsContext] : GSCurrentContext() );
    [self _lockFocusInContext: ctxt inRect: rect];
}

This appears to solve my problem, but it should be reviewed by  
someone who has a deeper knowledge.

Cheers,
Mark Tracy

> Message: 4
> Date: Wed, 28 Feb 2007 12:20:45 +0100
> From: Fred Kiefer <address@hidden>
> Subject: Changes to graphic context handling
> To: GNUstep Developer <address@hidden>
> Message-ID: <address@hidden>
> Content-Type: text/plain; charset=ISO-8859-15
>
> I am planing to implement some serious changes to NSGraphicsContext  
> and
> the way this class interacts with the rest of GNUstep and wanted to
> publish this plans first, so you may comment on them.
>
> Currently GNUstep uses mostly just one graphics context, the one  
> set up
> in NSApplication. Only for printing other graphics contexts get  
> created.
> The idea now is to let each window have its own graphics context.  
> There
> still would be the default graphics context owned by the NSApplication
> and the ones for printing. In addition, we may even have graphics
> contexts to draw into memory space.
>
> Why do this? One reason is of course to follow the change that  
> Apple has
> done for OS 10.4. With our current setup we could not implement  
> many of
> the methods on the class NSGraphicsContext nor some on NSView. Another
> reason is to get rid of the strange way we currently set up the gstate
> of a window, but this is a rather private reason. :-)
>
> The graphics context will be selected when ever a view does a lock
> focus. When this has happened everything will be as before, the  
> context
> returned by GSCurrentContext() will be the one for the active window.
> The difference will only be when no view has locked focus. Then a
> default context will be returned by this function. This context will
> mostly be used by events. Drawing on the default context should be
> regarded as an error. This may be a difference to the current state,
> where this drawing is silently ignored.
>
> Now, what is the real benefit of this change? It will allow us to
> implement drawing for PS, PDF and bitmap output more easily. Our  
> current
> PS solution works to a certain degree, but it is incompatible to  
> MacOSX.
>
> If nobody opposes this change, I will go ahead with it.
>
> Cheers,
> Fred