CATiledLayer blanking tiles before drawing contents

Posted by Greg Plesur on Stack Overflow See other posts from Stack Overflow or by Greg Plesur
Published on 2009-11-10T19:40:34Z Indexed on 2010/05/19 0:30 UTC
Read the original article Hit count: 516

All,

I'm having trouble getting behavior that I want from CATiledLayer. Is there a way that I can trigger the tiles to redraw without having the side-effect that their areas are cleared to white first? I've already subclassed CATiledLayer to set fadeDuration to return 0.

To be more specific, here are the details of what I'm seeing and what I'm trying to achieve:

  • I have a UIScrollView with a big content size...~12000x800. Its content view is a UIView backed by a CATiledLayer.
  • The UIView is rendered with a lot of custom-drawn lines
  • Everything works fine, but the contents of the UIView sometimes change. When that happens, I'd like to redraw the tiles as seamlessly as possible. When I use setNeedsDisplay on the view, the tiles redraw but they are first cleared to white and there's a fraction-of-a-second delay before the new content is drawn. I've already subclassed CATiledLayer so that fadeDuration is set to 0.
  • The behavior that I want seems like it should be possible...when you zoom in on the scrollview and the content gets redrawn at a higher resolution, there's no blanking before the redraw; the new content is drawn right on top of the old one. That's what I'm looking for.

Thanks; I appreciate your ideas.

Update:

Just to follow up - I realized that the tiles weren't being cleared to white before the redraw, they're being taken out entirely; the white that I was seeing is the color of the view that's beneath my CATiledLayer-backed view.

As a quick hack/fix, I put a UIImageView beneath the UIScrollView, and before triggering a redraw of the CATiledLayer-backed view I render its visible section into the UIImageView and let it show. This smooths out the redraw significantly.

If anyone has a better solution, like keeping the redraw-targeted tiles from going away before being redrawn in the first place, I'd still love to hear it.

© Stack Overflow or respective owner

Related posts about iphone

Related posts about iphone-sdk