StackOverflow2013

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PODrawrect with CGBitmapContext is too slow
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copied!<p>So I've got a basic drawing app in the process that allows me to draw lines. I draw to an off screen bitmap then present the image in <code>drawRect</code>. It works but its way too slow, updating about half a second after you've drawn it with your finger. I took the code and adapted it from this tutorial, <a href="http://www.youtube.com/watch?v=UfWeMIL-Nu8&feature=relmfu" rel="nofollow">http://www.youtube.com/watch?v=UfWeMIL-Nu8&feature=relmfu</a> , as you can see in the comments people are also saying its too slow but the guy hasn't responded.</p> <p>So how can I speed it up? or is there a better way to do it? any pointers will be appreciated.</p> <p>Heres the code in my <code>DrawView.m</code>. </p> <pre><code>-(id)initWithCoder:(NSCoder *)aDecoder { if ((self=[super initWithCoder:aDecoder])) { [self setUpBuffer]; } return self; } -(void)setUpBuffer { CGContextRelease(offscreenBuffer); CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); offscreenBuffer = CGBitmapContextCreate(NULL, self.bounds.size.width, self.bounds.size.height, 8, self.bounds.size.width*4, colorSpace, kCGImageAlphaPremultipliedLast); CGColorSpaceRelease(colorSpace); CGContextTranslateCTM(offscreenBuffer, 0, self.bounds.size.height); CGContextScaleCTM(offscreenBuffer, 1.0, -1.0); } -(void)drawToBuffer:(CGPoint)coordA :(CGPoint)coordB :(UIColor *)penColor :(int)thickness { CGContextBeginPath(offscreenBuffer); CGContextMoveToPoint(offscreenBuffer, coordA.x,coordA.y); CGContextAddLineToPoint(offscreenBuffer, coordB.x,coordB.y); CGContextSetLineWidth(offscreenBuffer, thickness); CGContextSetLineCap(offscreenBuffer, kCGLineCapRound); CGContextSetStrokeColorWithColor(offscreenBuffer, [penColor CGColor]); CGContextStrokePath(offscreenBuffer); } - (void)drawRect:(CGRect)rect { CGImageRef cgImage = CGBitmapContextCreateImage(offscreenBuffer); UIImage *image =[[UIImage alloc] initWithCGImage:cgImage]; CGImageRelease(cgImage); [image drawInRect:self.bounds]; } </code></pre> <p>Works perfectly on the simulator but not device, I imagine that's something to do with processor speed.</p> <p>I'm using ARC.</p>

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