Comments on: iOS 4, Why You So Slow?

By: Andy

Andy — Wed, 05 Oct 2011 00:26:17 +0000

This is _the_ fix for the poor 2D drawing performance in my iPad app. I can’t take advantage of this excellent advice without thanking you. Please keep up the good work.

I find it alarming that such an inferior approach as using CGContextDrawImage is not only part of the standard API, but is even recommended by authors of textbooks on the subject.

By: Aubada

Aubada — Wed, 10 Nov 2010 20:42:31 +0000

Thank you so much for sharing this solution, I had this problem and I am using drawText:InRect: in NSString, I’ll try this solution and give a feedback if anything happens…

Many thanks again…

By: mundue

mundue — Fri, 24 Sep 2010 01:12:42 +0000

@Dave,

In my view’s drawView method there’s a one-time init call, like this:

-(void)drawView:(QuartzView*)view inContext:(CGContextRef)context bounds:(CGRect)bounds
{
if ( !layersSetup )
[self setupLayersForView:(QuartzView*)view bounds:(CGRect)bounds];
…
}

An the setupSubLayersForView method a) populates a 2D array of layers and b) adds each one to the view’s layer. Looks like this, but many lines of code redacted:

- (void) setupLayersForView:(QuartzView*)view bounds:(CGRect)bounds {
…
for ( row = 0; row < numRows; row++ ) {
for ( column = 0; column < numColumns; column++ ) {
CALayer* layer = [CALayer layer];
layer.position = CGPointMake(x,y);
layer.bounds = CGRectMake(0.0, 0.0, width, height);
layer.contentsGravity = kCAGravityResize;
[[view layer] addSublayer:layer];
layers[row][column] = layer;
}
}
…
layersSetup = YES;
}

By: Dave

Dave — Mon, 20 Sep 2010 10:47:00 +0000

Great! But … How do you have initialized your CALayer? How have you linked it to your UIView?

By: Andrew

Andrew — Tue, 24 Aug 2010 00:47:18 +0000

Sadly I’m experiencing very similar problems when using UIImage drawInRect even on newer devices (read iPhone 4).

Performance is so bad that I’ve had to remove one of my apps from sale until I can get a fix from apple.

Logged Problem ID: 8291881 at bugreports.apple.com so I’ll post back if I hear anything further.

Thanks for all the info!

By: Tim

Tim — Sat, 31 Jul 2010 04:14:26 +0000

To answer my own question, after trying many things, I found what worked was to create a new CGImage each time the underlying data changed. When using the original CGContextDrawImage method, my data provider got called on each redraw so I did not need to recreate the CGImage. Still, this is a LOT faster!! Thanks.

By: Tim

Tim — Thu, 29 Jul 2010 23:53:14 +0000

Thanks, this seems to be exactly what I need. My problem is similar, except my CGImage data comes from a bitmap whose contents are created by a video decoder. Following your example works when the image first appears, but then how do I tell it when the contents of the CGImage have changed? I tried CALayer:setNeedsDisplay but then it stopped working at all. I already doing UIView:setNeedsDisplay. Thanks for any help; I am totally new to Core Animation.

By: mundue

mundue — Sun, 11 Jul 2010 19:25:35 +0000

Yes, in fact there is a radar bug, http://openradar.appspot.com/8134592. Several folks in the Dev Forums have reported similar slowness as well. Hopefully it will be fixed in the 4.0.1 update, or whatever is next.

By: bunnyhero

bunnyhero — Sun, 11 Jul 2010 02:58:03 +0000

fascinating. did you file a bug report? it would be nice if apple could fix this in future updates.

thanks for finding this out!