title: Big slowdown on ios7: CGContextDrawImage or UIView setImage?
body: <p>Ok, I have a serious problem with ios7. I have a code where the user drags a control, and as he drags, the interface is updated with a processed image. This was very fast until iOS 6.1, and now it's very slow.</p>
  
  <p>Here's how my code works:</p>
  
  <pre><code>- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
      //get initial position
  
  - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
      //calculates new position
  
      applyEffects();
  
  - (void)applyEffects {
  
      UIGraphicsBeginImageContext();
      //CGContextTranslateCTM, CGContextScaleCTM, CGContextDrawImage and stuff like that
      UIImage *blendedImage = UIGraphicsGetImageFromCurrentImageContext();
      UIGraphicsEndImageContext();
  
      preview.image = blendedImage; //preview is a UIImageView
  </code></pre>
  
  <p>Now the thing is, after logging, I realized applyEffects is getting called every time I move the finger on screen, but the view is being updated very very few times, and I think that's why it appears so slow.</p>
  
  <p>So, any idea on why "preview.image = blendedImage;" is not updating the view anymore? Am I missing something?</p>
  
  <p>Again, this only happens on iOS 7.</p>
  
  <p>Thank you in advance!</p>