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Re: fast blitting with Quartz
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Re: fast blitting with Quartz


  • Subject: Re: fast blitting with Quartz
  • From: Greg Titus <email@hidden>
  • Date: Fri, 28 Sep 2007 09:38:35 -0700

Hey Kenny,

(Long time no see!)

If you are using NSScrollView and NSClipView for your scrolling, then this is all built in for you. (See -setCopiesOnScroll: in NSClipView, which defaults to YES.) The clip view will do the blitting of your view content that was already on screen, and the rectangle passed into your view's -drawRect: method will just consist of the 1% of new data. So all you need to do to be efficient is to just make sure that you pay attention to the rectangle argument passed in to your - drawRect: and only draw that rectangle.

Hope this helps,
	- Greg

On Sep 28, 2007, at 9:28 AM, Kenny Leung wrote:

Hi All.

Part of this is more curiosity than anything, but I hope you will indulge me.

The situation is this: I would like to have very fast on-screen blitting to support a scrolling-chart like drawing.

In the old NeXTstep days of pswraps, there was this cool PostScript operator called "composite" that would blit bits in the current graphics context. So if you were doing a scrolling chart, you would just have to composite the 99% of stuff you already had on-screen, and draw the 1% of new data.

Question 1: Does anybody know of the current Quartz equivalent for doing this? I image that the NSScrollView/NSClipView combination knows how to do this, but I have not been able to find the function to do it.

Question 2: If you can no longer do this, what would be an efficient strategy to do this? Seems like the same could be achieved using 2 NSImages - composite 99% from one to the other, draw the 1%, composite on-screen, flip, rinse, lather, repeat. But that seems high on both memory usage, and takes one more composite than the optimal version.

Thanks for any insight into this!

-Kenny

P.S. If any of you remember my NeXTstep program KPerfmon, it used this trick.

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