There has been many Questions recently about drawing PDF's.
Yes, you can render PDF's very easily with a
UIWebView but this cant give the performance and functionality that you would expect from a good PDF viewer.
You can draw a PDF page to a CALayer or to a UIImage. Apple even have sample code to show how draw a large PDF in a Zoomable UIScrollview
But the same issues keep cropping up.
- PDF's in a
UIImagedon't optically scale as well as a Layer approach.
- The CPU and memory hit on generating
PDFcontextlimits/prevents using it to create a real-time render of new zoom-levels.
- Theres a significant Overhead (time)
drawing a full PDF page to a
CALayer: individual tiles can be seen rendering (even with a tileSize tweak)
CALayerscant be prepared ahead of time (rendered off-screen).
Generally PDF viewers are pretty heavy on memory too. Even monitor the memory usage of apple's zoomable PDF example.
In my current project, I'm developing a PDF viewer and am rendering a
UIImage of a page in a separate thread (issues here too!) and presenting it while the scale is x1.
CATiledLayer rendering kicks in once the scale is >1. iBooks takes a similar double take approach as if you scroll the pages you can see a lower res version of the page for just less than a second before a crisp version appears.
Im rendering 2 pages each side of the page in focus so that the PDF image is ready to mask the layer before it starts drawing.Pages are destroyed again when they are +2 pages away from the focused page.
Does anyone have any insights, no matter how small or obvious to improve the performance/ memory handling of Drawing PDF's? or any other issues discussed here?
EDIT: Some Tips (Credit- Luke Mcneice,VdesmedT,Matt Gallagher,Johann):
Save any media to disk when you can.
Use larger tileSizes if rendering on TiledLayers
init frequently used arrays with placeholder objects, alternitively another design approach is this one
Note that images will render faster than a
NSOperationsor GCD & Blocks to prepare pages ahead of time.
CGContextSetInterpolationQuality(ctx, kCGInterpolationHigh); CGContextSetRenderingIntent(ctx, kCGRenderingIntentDefault);before
CGContextDrawPDFPageto reduce memory usage while drawing
NSOperationswith a docRef is a bad idea (memory), wrap the docRef into a singleton.
NSOperationsWhen you can, especially if they will be using memory, beware of leaving contexts open though!
Recycle page objects and destroy unused views
Close any open Contexts as soon as you don't need them
on receiving memory warnings release and reload the DocRef and any page Caches
Other PDF Features:
Getting Links inside a PDF (and here and here)
Getting the target of the link (Getting the page number from the
Getting Raw Text (and here and Here and here (positioning focused))
Searching(and here) (doesn't work with all PDFs (some just show weird characters, I guess it's an encoding issue but I'm not sure) -Credit BrainFeeder)
CALayer and Off-Screen Rendering - render the next page for fast/smooth display
- Quartz PDFObjects (Used for meta info, annotations, thumbs)
- Abobe PDF Spec
- Apple/ ZoomingPDF - zooming,
- vfr/ reader - zooming, paging,
- brow/ leaves - paging with nice transitions
- / skim - everything it seems (PDF reader/editor for OSX)
PSPDFKit, it is not cheap, but worth: pspdfkit.com – János