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Re: rotating an object around the center of a view




On Mar 4, 2007, at 4:27 PM, Ken Tozier wrote:


On Mar 4, 2007, at 7:01 PM, Bob Smith wrote:

You do not have to do all the view drawing in the same coordinate system. Also repeatedly transforming the paths you are drawing does not seem like the best approach. Better to save and restore graphics state to draw the bits in different coordinate systems, so your graphics model objects can be static. Your -drawRect would look conceptually like this:

One thing about your method that's not immediately obvious to me is why it's more efficient to apply all these transforms to the entire coordinate system of a view than just rotate a bezier path within the view. It seems like, at least intuitively, that transforming a small part of a view (the hands) would be much more efficient.

The "entire" coordinate system is simply a drawing context with some state information. One aspect of that context is the current transform. The current transform only really does something when you go to draw. It doesn't change what you may have drawn already, etc.


-Shawn
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References: 
 >Re: rotating an object around the center of a view (From: Erik Buck <email@hidden>)
 >Re: rotating an object around the center of a view (From: Ken Tozier <email@hidden>)
 >Re: rotating an object around the center of a view (From: Bob Smith <email@hidden>)
 >Re: rotating an object around the center of a view (From: Ken Tozier <email@hidden>)



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