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Flipped view confusion

Subject: Flipped view confusion
From: Seth Pellegrino <email@hidden>
Date: Tue, 31 Jul 2007 11:55:38 -0400
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Hello list,

I was working on a project involving getting a NSTextFieldCell to use only part of its bounding rect when I noticed some odd behavior. Everything worked perfectly when the text wasn't being selected or edited (i.e. drawWithFrame was called), but every time I caused a call to either selectWithFrame or editWithFrame graphical artifacts appeared.

I eventually tracked the problem down to NSGraphicsContext's - isFlipped method. When -isFlipped was called on the current graphical context, it returned YES in drawWithFrame and NO in both editWithFrame and selectWithFrame. Oddly, calling -isFlipped on the controlView for my cell returned the correct (YES) value in all three. What is causing the current context to lie and say the opposite of the control view? I'm using a 1x1 NSMatrix to contain my cell as it seemed to be a good testbed.

As a simple "Try it at home" example, all it takes is a 1x1 NSMatrix with a custom NSTextFieldCell. If the -drawWithFrame, -editWithFrame, and -selectWithFrame methods are overridden as:

- (void)drawWithFrame:(NSRect)cellFrame inView:(NSView *)controlView { NSLog(@"drawWithFrame: control: %d graphicsContext: %d", [controlView isFlipped], [[NSGraphicsContext currentContext] isFlipped]);

        [super drawWithFrame:cellFrame inView:controlView];
}

-(void)editWithFrame:(NSRect)cellFrame inView:(NSView *)controlView editor:(NSText *)textObj delegate:(id)anObject event:(NSEvent *)theEvent { NSLog(@"editWithFrame: control: %d graphicsContext: %d", [controlView isFlipped], [[NSGraphicsContext currentContext] isFlipped]);

[super editWithFrame:cellFrame inView:controlView editor:textObj delegate:anObject event:theEvent]; } -(void)selectWithFrame:(NSRect)cellFrame inView:(NSView *)controlView editor:(NSText *)textObj delegate:(id)anObject start:(int)selStart length:(int)selLength { NSLog(@"selectWithFrame: control: %d graphicsContext: %d", [controlView isFlipped], [[NSGraphicsContext currentContext] isFlipped]);

[super selectWithFrame:cellFrame inView:controlView editor:textObj delegate:anObject start:selStart length:selLength]; }


you will see output similar to:

TestFlipped[284] selectWithFrame: control: 1 graphicsContext: 0
TestFlipped[284] drawWithFrame: control: 1 graphicsContext: 1
TestFlipped[284] editWithFrame: control: 1 graphicsContext: 0

Any help with understanding what's happing would be greatly appreciated. Also, as a general rule, which isFlipped method would be better to use, as they seem to be non-equivalent?

Thanks,

Seth
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