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POFast and Lean PDF Viewer for iPhone / iPad / iOs - tips and hints?
 

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    <p>There has been many Questions recently about drawing PDF's. </p> <p>Yes, you can render PDF's very easily with a <code>UIWebView</code> but this cant give the performance and functionality that you would expect from a good PDF viewer.</p> <p>You can draw a PDF page <a href="http://www.cocoabuilder.com/archive/cocoa/196313-display-pdf-in-calayer.html" rel="noreferrer">to a CALayer</a> or <a href="https://stackoverflow.com/questions/3831304/calayer-and-off-screen-rendering/3853778#3853778"> to a UIImage</a>. Apple even have sample code to show how draw a large PDF <a href="http://developer.apple.com/library/ios/#samplecode/ZoomingPDFViewer/Introduction/Intro.html#//apple_ref/doc/uid/DTS40010281" rel="noreferrer">in a Zoomable UIScrollview</a></p> <p>But the same issues keep cropping up.</p> <p><strong>UIImage Method:</strong></p> <ol> <li>PDF's in a <code>UIImage</code> don't optically scale as well as a Layer approach.</li> <li>The CPU and memory hit on generating the <code>UIImages</code> from a <code>PDFcontext</code> limits/prevents using it to create a real-time render of new zoom-levels.</li> </ol> <p><strong>CATiledLayer Method:</strong></p> <ol start="3"> <li>Theres a significant Overhead (time) drawing a full PDF page to a <code>CALayer</code>: individual tiles can be seen rendering (even with a tileSize tweak)</li> <li><code>CALayers</code> cant be prepared ahead of time (rendered off-screen).</li> </ol> <p>Generally PDF viewers are pretty heavy on memory too. Even monitor the memory usage of apple's zoomable PDF example.</p> <p>In my current project, I'm developing a PDF viewer and am rendering a <code>UIImage</code> of a page in a separate thread (issues here too!) and presenting it while the scale is x1. <code>CATiledLayer</code> 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.</p> <p>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.</p> <p><strong>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?</strong></p> <p><strong><em>EDIT:</em></strong> Some Tips (Credit- Luke Mcneice,VdesmedT,Matt Gallagher,Johann):</p> <ul> <li><p>Save any media to disk when you can.</p></li> <li><p>Use larger tileSizes if rendering on TiledLayers</p></li> <li><p>init frequently used arrays with placeholder objects, alternitively another design approach is <a href="http://cocoawithlove.com/2009/01/multiple-virtual-pages-in-uiscrollview.html" rel="noreferrer">this one</a></p></li> <li><p>Note that images will render faster than a <code>CGPDFPageRef</code></p></li> <li><p>Use <code>NSOperations</code> or GCD &amp; <a href="http://thirdcog.eu/pwcblocks/" rel="noreferrer">Blocks</a> to prepare pages ahead of time.</p></li> <li><p>call <code>CGContextSetInterpolationQuality(ctx, kCGInterpolationHigh); CGContextSetRenderingIntent(ctx, kCGRenderingIntentDefault);</code> before <code>CGContextDrawPDFPage</code> to reduce memory usage while drawing </p></li> <li><p>init'ing your <code>NSOperations</code> with a docRef is a bad idea (memory), wrap the docRef into a singleton.</p></li> <li><p>Cancel needless <code>NSOperations</code> When you can, especially if they will be using memory, beware of leaving contexts open though!</p></li> <li><p>Recycle page objects and destroy unused views</p></li> <li><p>Close any open Contexts as soon as you don't need them</p></li> <li><p>on receiving memory warnings release and reload the DocRef and any page Caches</p></li> </ul> <p><strong>Other PDF Features:</strong></p> <ul> <li><p><a href="https://stackoverflow.com/questions/3257057/iphone-cgpdfdocument-pdf-links">Getting Links inside a PDF</a> (and <a href="https://stackoverflow.com/questions/4080373/get-pdf-hyperlinks-on-ios-with-quartz">here</a> and <a href="http://pastebin.com/69JW1Kkc" rel="noreferrer">here</a>)</p> <ul> <li><p><a href="https://stackoverflow.com/questions/4255298/how-does-an-annot-cgpdfdictionary-rect-translate-to-objective-c-points/4255586#4255586">Understanding the PDF Rect for link positioning</a></p></li> <li><p><a href="https://stackoverflow.com/questions/4303394/converting-adobe-pdf-date-string-to-nsdate">Converting PDF annot datestrings</a></p></li> <li><p><a href="https://stackoverflow.com/questions/4643489/how-do-i-retrieve-a-page-number-or-page-reference-for-an-outline-destination-in-a/4683905#4683905">Getting the target of the link</a> (Getting the page number from the <code>/Dest</code> array)</p></li> </ul></li> <li><p><a href="https://stackoverflow.com/questions/2556344/create-a-table-of-contents-from-a-pdf-file">Getting a table of contents</a></p></li> <li><p><a href="https://stackoverflow.com/questions/5881921/get-cgpdfdocumentref-name-of-document/5912618#5912618">Document title</a> and <a href="http://www.iphonedevsdk.com/forum/iphone-sdk-development/29770-pdf-title-keywords-label.html" rel="noreferrer">Keywords</a></p></li> <li><p><a href="https://stackoverflow.com/questions/2556344/create-a-table-of-contents-from-a-pdf-file/3427596#3427596">Getting Raw Text</a> (and <a href="https://stackoverflow.com/questions/2960195/extracting-pdf-text-in-objective-c">here</a> and <a href="https://stackoverflow.com/questions/3627745">Here</a> and <a href="https://stackoverflow.com/questions/3627745/getting-text-position-while-parsing-pdf-with-quartz-2d">here</a> (positioning focused))</p></li> <li><p><a href="http://blog.random-ideas.net/?p=184" rel="noreferrer">Searching</a>(and <a href="https://stackoverflow.com/questions/4097044/pdf-search-on-the-iphone">here</a>) (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)</p></li> <li><p><a href="https://stackoverflow.com/questions/3831304/calayer-and-off-screen-rendering">CALayer and Off-Screen Rendering</a> - render the next page for fast/smooth display</p></li> </ul> <p><strong>Documentation</strong></p> <ul> <li><a href="http://developer.apple.com/library/mac/#documentation/GraphicsImaging/Reference/CGPDFObject/Reference/reference.html" rel="noreferrer">Quartz PDFObjects</a> (Used for meta info, annotations, thumbs) </li> <li><a href="http://www.adobe.com/devnet/pdf/pdf_reference.html" rel="noreferrer">Abobe PDF Spec</a> </li> </ul> <p><strong>Example projects</strong></p> <ul> <li><a href="http://developer.apple.com/library/ios/#samplecode/ZoomingPDFViewer/Introduction/Intro.html#//apple_ref/doc/uid/DTS40010281" rel="noreferrer">Apple/ ZoomingPDF</a> - zooming, <code>UIScrollView</code>, <code>CATiledLayer</code></li> <li><a href="https://github.com/vfr/Reader" rel="noreferrer">vfr/ reader</a> - zooming, paging, <code>UIScrollView</code>, <code>CATiledView</code></li> <li><a href="https://github.com/brow/leaves" rel="noreferrer">brow/ leaves</a> - paging with nice transitions </li> <li><a href="http://skim-app.sourceforge.net/developers.html" rel="noreferrer">/ skim</a> - everything it seems (PDF reader/editor for OSX)</li> </ul>
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    1. COedited with some basic tips
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    2. COcommenting to ensure peeps get the edit notification
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    3. CO+1 and thanks for adding all this info, wish I had it when I was developing my reader ;) also thanks for adding my question about PDF annotations (it also contains the answers with sample code). a few days ago I opened this: http://stackoverflow.com/questions/4097044/pdf-search-on-the-iphone do you have any tips?
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