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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 11:35:29 -0700


On Sep 28, 2007, at 11:27 AM, Scott Thompson wrote:


On Sep 28, 2007, at 12:53 PM, Wade Tregaskis wrote:

I suppose should be no problem to letting the size of the view grow to infinity - as long as I'm not drawing any more of it. I guess I just have to get over the mental hurdle.

Note that there is a practical limit to the size of an NSView, beyond which all sorts of funkiness occurs (visible as drawing artefacts) as a consequence of CoreGraphics using floats, and thus having very much finite precision. It depends on your particular code as to when exactly you'll see problems, but I wouldn't let any view (inside a scrollview) get more than 10,000,000 pixels in any dimension.


(I know that sounds huge, but it's pretty easy to naively hit if you're not careful)

Are you sure about the magnitude of your dimension there? I was under the impression (potentially mistaken) that the problems started around 10,000 (ten thousand) instead of 10,000,000 (10 million).

Nope, it's somewhat less than 10 million but much much larger than 10 thousand. That's about the point where the "float" type no longer has enough precision to represent individual pixels.


An IEEE binary float has 1 bit of sign, 8 bits of exponent, and 23 bits of fractional value. Which means you should be able to exactly represent pixel values between +8,388,608 and -8,388,608. (2^23)

	- Greg
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  • Follow-Ups:
    • Re: fast blitting with Quartz
      • From: Greg Titus <email@hidden>
    • Re: fast blitting with Quartz
      • From: Scott Thompson <email@hidden>
References: 
 >fast blitting with Quartz (From: Kenny Leung <email@hidden>)
 >Re: fast blitting with Quartz (From: Greg Titus <email@hidden>)
 >Re: fast blitting with Quartz (From: Kenny Leung <email@hidden>)
 >Re: fast blitting with Quartz (From: Wade Tregaskis <email@hidden>)
 >Re: fast blitting with Quartz (From: Scott Thompson <email@hidden>)

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