Re: Erasing drawn content
Re: Erasing drawn content
- Subject: Re: Erasing drawn content
- From: Matej Bukovinski <email@hidden>
- Date: Wed, 9 Jun 2010 20:06:47 +0200
The clipping path approach doesn't really help. It turns out that you can only intersect the current clipping path (initially the view's bounds) with a new path and the intersected region is the region where drawing is visible. This means that when you're drawing a larger rectangle over a smaller one, you would need to set the clipping path to all areas NOT covered by the smaller rectangle. This is basically the same problem as calculating which parts of the larger rectangle to draw and just drawing there.
The layer approach din't work out as well. I get the same black color problem as with the view.
Overriding drawRect: is problematic for WebViews, as Jens pointed out WebViews do all sorts of drawing voodoo. Believe me, I've tried.
It seems that the only option left manually doing difference operations (or doing an overlay window) on the rectangles and drawing only the uncovered portions. Set operations on NSBezierPath would definitely help. I found a nice category on cocoadev (http://www.cocoadev.com/index.pl?NSBezierPathcombinatorics) but it uses the General Polygon Clipper (which I won't be able to use due to licensing issues). Does perhaps anyone else know of a convenient method (library) to do difference operations on rectangular shapes (i.e., draw a NSRect but not the points that are in an array of other NSRects)?
> If the clipping path method works, and if you can subclass your webview, then you shouldn't need a separate view at all. Just override drawRect: and draw your rectangles after calling super. It sounds almost too easy.
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