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POQuartz2D and Clipping - Optimize this drawing routine?
 

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    <p>I'm new to Quartz2d so I hope this is an easy question to answer. </p> <p>I have a scrollview whose content frame is 1024x768. Within this I push a custom view (with frame 1024x768) that uses Quartz2d to do some drawing. The idea is, I have a large area that the user can scroll around to see different parts.</p> <p>The problem I'm having is, when I scroll on the device I get memory warning errors or terrible scrolling performance. This is no doubt because I am re-drawing the entire 1024x768 field. I thought that setting the clipping path to the UIScrollView offset would help.. and it does.. until i scroll.. in which case the view does not redraw until scrolling stops. telling the view to draw during scrollViewDidScroll also results in bad performance</p> <p>can anyone tell me how i can optimize my drawing routine?</p> <p>i have two images.. one of which is getting masked, and both being painted to the screen (one on top of the other)</p> <p><code> - (void)drawRect:(CGRect)dirtyRect {</p> <pre><code>CGContextRef myContext = UIGraphicsGetCurrentContext(); // get our offset (where we've scrolled to) CGPoint offset = scrollView.contentOffset; // clip to our offset.. uncomment for good performance but terrible scrolling //CGContextClipToRect(myContext, CGRectMake(offset.x, offset.y, 480, 320)); // make an image from the mask context CGImageRef aMaskImage = CGBitmapContextCreateImage (myMaskContext); // mask the first image CGImageRef aImage = CGImageCreateWithMask(myImageRef1, aMaskImage); CGContextDrawImage(myContext, CGRectMake(0, 0, self.frame.size.width, self.frame.size.height), myImageRef1); CGContextDrawImage(myContext, CGRectMake(0, 0, self.frame.size.width, self.frame.size.height), aImage); CGImageRelease(aImage); CGImageRelease(aMaskImage); </code></pre> <p>}</p> <p></code></p> <p>thanks in advance for any help you can provide!</p>
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