Drawing line in UIImageView - ios

Question

I have a UIImageView (wImage) in which I am trying to draw a line. The code runs fine in simulator but when I test it an a device it is super slow and creates a memory warning. Could someone please tell me what the problem is?
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [touches anyObject];
CGPoint thirdPoint = lastPoint;
lastPoint = [touch previousLocationInView:self.view];
CGPoint currentPoint = [touch locationInView:self.view];
CGPoint mid1 = CGPointMake((lastPoint.x+thirdPoint.x)/2, (lastPoint.y+thirdPoint.y)/2);
CGPoint mid2 = CGPointMake((currentPoint.x+lastPoint.x)/2, (currentPoint.y+lastPoint.y)/2);
UIGraphicsBeginImageContext(wImage.frame.size);
CGContextSetAllowsAntialiasing(UIGraphicsGetCurrentContext(), true);
CGContextSetShouldAntialias(UIGraphicsGetCurrentContext(), true);
[wImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), mid1.x, mid1.y);
CGContextAddQuadCurveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y, mid2.x, mid2.y);
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brush );
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, 1);
CGContextSetBlendMode(UIGraphicsGetCurrentContext(),kCGBlendModeNormal);
CGContextStrokePath(UIGraphicsGetCurrentContext());
wImage.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
}

Answer 1

You are having such a performance problem because you are actually doing a ton of work to create a new image every time the user's finger moves. Don't draw directly on the image itself, create a UIView that is responsible for the user's drawing, with a transparend background. There's a good amount you can do with it, and I couldn't possibly put all the code here, but there is a great tutorial, complete with some really cool code to smooth out the line as the user is drawing. It results in a much nicer looking path. Here it is:
http://code.tutsplus.com/tutorials/smooth-freehand-drawing-on-ios--mobile-13164
Go ahead and read through all the sections - it would be good for you to understand what's going on rather than just trying the last implementation.
For your implementation, make sure the view has a transparent background, so you can see the ImageView underneath.