iPhone/iPad draw pdf like iBooks?

Does anyone know how to use core graphics to draw a pdf like in iBooks. I can already draw a pdf page using core graphics but was curious how iBooks shows a lower quality view of each page so it loads fast and then when you stay on a page longer it renders it a full开发者_StackOverflow社区 quality. This makes it able to open the pdf without having to make the user wait like most magazine apps you see on ipad. Any ideas would help!

Apple have some "ZoomingPDFViewer" sample code:

http://developer.apple.com/library/ios/#samplecode/ZoomingPDFViewer/Introduction/Intro.html#//apple_ref/doc/uid/DTS40010281

I suspect that might give you some good ideas :-)

I assume they use multiple layers, the first layer loads the pdf in low resolution and the better resolution is prepared in the background. When ready these layers are swapped.

Have a look at CGPDFDocumentRef and CATiledLayer in the documentation.