Re: scrolling an NSImageView leaves tracks

FROM : John Pannell
DATE : Sat Apr 09 23:50:40 2005

Hi Geoff-

I have successfully used the following technique to eliminate tearing 
artifacts when scrolling a matrix of images; I imagine it should work 
with a single image as well.

1.  Tell the NSScrollView's NSClipView to post notifications when its 
bounds change.
2.  Tell your controller object to observe such notifications.

[[[aScrollView subviews] objectAtIndex:0] 
setPostsBoundsChangedNotifications:YES];
[[NSNotificationCenter defaultCenter] addObserver:self 
selector:@selector(scrollChanged:) name:nil object:[[aScrollView 
subviews] objectAtIndex:0]];

3.  In your controller's observer method, tell the NSImageView it needs 
display.

[anImageView setNeedsDisplay:YES];

With any luck, this will result in "clean up" after the scrolling 
movement to eliminate the artifacts.  Hope this helps!

John

John Pannell
Positive Spin Media
http://www.positivespinmedia.com

On Apr 9, 2005, at 1:53 PM, Geoff Levner wrote:

> I have an NSImageView in an NSScrollView. I can zoom in and out, 
> scroll, load new images, and everything is fine.
>
> Except for one thing. Sometimes, when a newly loaded image is 
> initially framed so that it is clipped by the scroll view, scrolling 
> leaves tracks (grey vertical or horizontal lines) where previously 
> clipped portions of the image become visible.  Zooming in or out once 
> makes them go away.  Calling the NSClipView's setCopiesOnScroll method 
> with NO also makes the problem go away, but then, of course, scrolling 
> is much slower.
>
> Has anybody out there ever encountered this sort of behavior?
>
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