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Re: Scrolling Text Algorithm for a Screen Saver
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Re: Scrolling Text Algorithm for a Screen Saver


  • Subject: Re: Scrolling Text Algorithm for a Screen Saver
  • From: Ricky Sharp <email@hidden>
  • Date: Mon, 30 Oct 2006 07:44:08 -0600


On Oct 30, 2006, at 6:26 AM, Alastair Houghton wrote:

On 30 Oct 2006, at 09:34, Doug Fort wrote:

I'm working on a screen saver. It involves scrolling text across the
screen. I'm using the simplest algorithm I could think of: calls to
NSString drawAtPoint:withAttributes: with the point moving a fixed
offset at each call to animateOneFrame. This works Ok at low scrolling
speeds, but at higher speeds (i.e. a larger offset), the motion
appears jerky.


I'm working on improving my code to minimize the amount of computation
in animateOneFrame. However, if anyone can suggest a better algorithm
for scrolling text, I'd appreciate it.

Using NSString's drawing methods will be inefficient because it will re-do the text layout every time. You should probably look at using the Cocoa Text system's NSLayoutManager object to do the layout once and then you can render the string over and over again with much lower overhead.


An alternative to that might be to render it once into a bitmap, and scroll the bitmap across the display instead. That approach would also mean you could use OpenGL if you wanted rather than Quartz.

And you can get really fancy by adding in motion blur (depending upon the speed of the scrolling). I haven't done this myself, but I believe this is doable via CoreImage.


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Ricky A. Sharp         mailto:email@hidden
Instant Interactive(tm)   http://www.instantinteractive.com

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References: 
 >Scrolling Text Algorithm for a Screen Saver (From: "Doug Fort" <email@hidden>)
 >Re: Scrolling Text Algorithm for a Screen Saver (From: Alastair Houghton <email@hidden>)

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