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

there has been many questions drawing pdf's.

yes, can render pdf's uiwebview cant give performance , functionality expect pdf viewer.

you can draw pdf page to calayer or uiimage. apple have sample code show how draw large pdf in zoomable uiscrollview

but same issues keep cropping up.

uiimage method:

1. pdf's in uiimage don't optically scale layer approach.
2. the cpu , memory hit on generating uiimages pdfcontext limits/prevents using create real-time render of new zoom-levels.

catiledlayer method:

3. theres significant overhead (time) drawing full pdf page calayer: individual tiles can seen rendering (even tilesize tweak)
4. calayers cant prepared ahead of time (rendered off-screen).

generally pdf viewers pretty heavy on memory too. monitor memory usage of apple's zoomable pdf example.

in current project, i'm developing pdf viewer , rendering uiimage of page in separate thread (issues here too!) , presenting while scale x1. catiledlayer rendering kicks in once scale >1. ibooks takes similar double take approach if scroll pages can see lower res version of page less second before crisp version appears.

im rendering 2 pages each side of page in focus pdf image ready mask layer before starts drawing.pages destroyed again when +2 pages away focused page.

does have insights, no matter how small or obvious improve performance/ memory handling of drawing pdf's? or other issues discussed here?

edit: tips (credit- luke mcneice,vdesmedt,matt gallagher,johann):

• save media disk when can.

• use larger tilesizes if rendering on tiledlayers

• init used arrays placeholder objects, alternitively design approach this one

• note images render faster cgpdfpageref

• use nsoperations or gcd & blocks prepare pages ahead of time.

• call cgcontextsetinterpolationquality(ctx, kcginterpolationhigh); cgcontextsetrenderingintent(ctx, kcgrenderingintentdefault); before cgcontextdrawpdfpage reduce memory usage while drawing

• init'ing nsoperations docref bad idea (memory), wrap docref singleton.

• cancel needless nsoperations when can, if using memory, beware of leaving contexts open though!

• recycle page objects , destroy unused views

• close open contexts don't need them

• on receiving memory warnings release , reload docref , page caches

other pdf features:

• getting links inside pdf (and here , here)

  • understanding pdf rect link positioning

  • converting pdf annot datestrings

  • getting target of link (getting page number /dest array)

• getting table of contents

• document title , keywords

• getting raw text (and here , here , here (positioning focused))

• searching(and here) (doesn't work pdfs (some show weird characters, guess it's encoding issue i'm not sure) -credit brainfeeder)

• calayer , off-screen rendering - render next page fast/smooth display

documentation

• quartz pdfobjects (used meta info, annotations, thumbs)
• abobe pdf spec

example projects

• apple/ zoomingpdf - zooming, uiscrollview, catiledlayer
• vfr/ reader - zooming, paging, uiscrollview, catiledview
• brow/ leaves - paging nice transitions
• / skim - seems (pdf reader/editor osx)

i have build such kind of application using approximatively same approach except :

• i cache generated image on disk , generate 2 3 images in advance in separate thread.
• i don't overlay uiimage instead draw image in layer when zooming 1. tiles released automatically when memory warnings issued.

whenever user start zooming, acquire cgpdfpage , render using appropriate ctm. code in - (void)drawlayer: (calayer*)layer incontext: (cgcontextref) context :

cgaffinetransform currentctm = cgcontextgetctm(context);     if (currentctm.a == 1.0 && baseimage) {     //calculate ideal scale     cgfloat scaleforwidth = baseimage.size.width/self.bounds.size.width;     cgfloat scaleforheight = baseimage.size.height/self.bounds.size.height;      cgfloat imagescalefactor = max(scaleforwidth, scaleforheight);      cgsize imagesize = cgsizemake(baseimage.size.width/imagescalefactor, baseimage.size.height/imagescalefactor);     cgrect imagerect = cgrectmake((self.bounds.size.width-imagesize.width)/2, (self.bounds.size.height-imagesize.height)/2, imagesize.width, imagesize.height);     cgcontextdrawimage(context, imagerect, [baseimage cgimage]); } else {     @synchronized(issue) {          cgpdfpageref pdfpage = cgpdfdocumentgetpage(issue.pdfdoc, pageindex+1);         pdftopagetransform = cgpdfpagegetdrawingtransform(pdfpage, kcgpdfmediabox, layer.bounds, 0, true);         cgcontextconcatctm(context, pdftopagetransform);             cgcontextdrawpdfpage(context, pdfpage);     } } 

issue object containg cgpdfdocumentref. synchronize part access pdfdoc property because release , recreate when receiving memorywarnings. seems cgpdfdocumentref object internal caching did not find how rid of.