title: Variable size of CGContext
body: <p>I'm currently using a <code>UIGraphicsBeginImageContext(resultingImageSize);</code> to create an image.</p>
  
  <p>But when I call this function, I don't know exactly the width of <code>resultingImageSize</code>.<br>
  Indeed, I developed some kind of video processing which consume lots of memory, and I cannot process first then draw after: I must draw <em>during</em> the video process.</p>
  
  <p>If I set, for example <code>UIGraphicsBeginImageContext(CGSizeMake(300, 400));</code>, the drawn part over 400 is lost.</p>
  
  <p>So is there a solution to set a variable size of CGContext, or resize a CGContext <strong>with very few memory consume</strong>?</p>