title: Drawing image with CoreGraphics on Retina iPad is slow
body: <p>In my iPad app, I am rendering to an offscreen bitmap, and then drawing the bitmap to the screen. (This is because I want to re-use existing bitmap rendering code.) On the iPad 2, this works like a charm, but on the new iPad with Retina display, drawing the bitmap is really slow, even though its resolution is still the same.</p>
  
  <p>To draw the bitmap, we use the regular Quartz 2D functions: <code>CGImageCreate</code> with a data provider created by <code>CGDataProviderCreateWithData</code>, 32-bit RGBA format with <code>kCGImageAlphaNoneSkipLast</code>. In the <code>UIView</code> that displays the bitmap, in <code>drawRect:</code>, we use <code>CGContextDrawImage</code> to draw it to the context returned by <code>UIGraphicsGetCurrentContext</code>.</p>
  
  <p>Note that I'm not even trying to draw at double resolution: for now I'm fine with the same resolution as I was using on the iPad 2. It looks like CoreGraphics is internally doubling the pixels, and then sending that to the GPU, even though the <code>CGImage</code> that I'm making should be fine for passing to the GPU directly. Any ideas?</p>