Looking at the QuartzDemo sample application, I love the speed of the PDF rending using quartz alone (that is, without using uiwebview). However, when I'm zooming in the PDF it doesn't seem to become more clear like it does in PDF view.
The simplest way to do achieve this is to implement a CATiledLayer based View and add it as subview of a UIScrollView.
Set the levelsOfDetail to 3 and levelsOfDetailBias to 2 for example (one zoom out level and two zoom in level).
The UIScrollView and CATiledLayer classes will do all the job for you :-)
It's actually just zooming in on a pre-rendered image of the PDF, so it's akin to scaling up a png or similar. To actually zoom the PDF you need to re-render the pdf at a larger scale factor and display only the rect that should be visible.
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I have a big UIimage (2000x2000). Image drawed every time on app start, and copied to CALayer.
On Current time i put UIScrollView on main view, and make CALayer with drawn image.
Scrolling on small zoom looks fine. But on min zooming , when whole image visible, image scroll slowed, it becomes not quick responsible on move touch.
So, the question. What can I do, to increase scrolling performance?
The approach I would take is to use a lower resolution version of your image at lower zoom levels (lower = zoomed out).
First, see this post for resizing UIImages.
Respond to the scrollViewDidEndZooming:withView:atScale: method in UIScrollViewDelegate, and switch the images when a certain zoom level is reached. This will take some trial and error to find the correct balance. You may even want to render your image at several different resolutions. Be sure to generate the different sized UIImages in advance so there is no delay while zooming.
I'm developing an app that must show one of three shapes(UIImageViews) depending on which button the user taps. I'm achieving this by creating different UIImageViews with three UIImages. I was wondering, is it more efficient if I draw the shapes directly from code??
BTW, the images have transparency and are 342 px x 388 px. Thanks!
It depends on the shapes. I suggest using PNG image files unless you are having particular speed issues. This lets the designers/artists customize the look easily rather than making the programmers do it in code, which is more tedious to modify.
We have some nice gradients and shadows in our application and drawing them using Quartz was pretty slow -- fine for a single screen, but too slow when animated or scrolled.
I'm trying to understand Apple's example code for the ZoomingPDFViewer. Here are some questions that I have in my understanding of how it works in my mind. I'm not really sure if I understand it correctly. The link for their code is at: http://developer.apple.com/library/ios/#samplecode/ZoomingPDFViewer/Introduction/Intro.html
(1) CATiledLayer is used to represent the PDF at different zoom levels. I'm assuming that's what this class is used for looking at the Class Reference. Would you ever use something else besides this class for a zooming function?
(2) in the initWithFrame for TiledPDFView, they do: tiledLayer.tileSize = CGSizeMake(512.0, 512.0); Is the tileSize the tiles that make up for the whole image? If so, why such a large size?
(3) How does the oldPDFView and pdfView work? Like which one is in front at the different stages of zoom, and when do they get swapped out. I'm having a hard time understanding the flow of the logic. Thanks.
(1) If you don't require the level of detail to vary for different zoom levels, or if the PDF loads fast enough to not warrant drawing a couple of tiles at a time, a regular UIView with a regular CALayer will work fine. For instance, if you were displaying an image instead of a PDF, and the image loads fast enough to not cause a performance snag, you would not need the asynchronous loading that CATiledLayer provides. The PhotoScroller sample uses both the tiled and non-tiled approaches if you want to compare them.
(2) The tileSize attribute changes the size of the blocks the layer should be split into. You can set this to whatever you want. 512x512 really isn't all that large, especially if your PDF dimensions are big. The default is 256x256.
(3) Anytime you start to zoom, oldPDFView is removed and released. Then pdfView is assigned to oldPDFView. When the zooming ends, a new pdfView is created with the change in scale and added on top of the old one. If the new scale is an increase, the new pdfView will be drawn with a higher level of detail. This makes it so you can zoom deeper and deeper into the PDF. The maximumZoomScale and minimumZoomScale only restrict how much you can zoom with an individual gesture.
Case: I have a simple piece of code for displaying/zooming/scrolling a large image in an UIImageView->UIScrollView. In this UIScrollView content I want to place buttons to create clickable areas.
Issue: When I zoom in the quality remains proper but, when I zoom out to the highest posible level than the image is getting dotted and some lines aren't visible anymore.
Tried: I tried to regenerate the UIImage with Interpolation Quality on kCGInterpolationHigh and tried to change the size of the image after every zoom change. As you might aspect, no results jet.
I suggest you use a CATiledLayer as the backing layer, as demonstrated by Apple's PhotoScroller sample app. This allows you to prebuild the scaled versions, meaning you can precisely control the interpolation quality with Photoshop/ImageMagick/GIMP etc, rather than relying on UIScrollView's built-in scaling.
I have been trying to render PDF documents into a CATiledLayer, but this appears to be slowing down the rendering process on the iPad.
I've also tried using a normal layer, but I've not seen an improvement.
Is there any alternative to using a CATiledLayer for rendering a PDF?
CATiledLayer is necessary either by itself or as a backing layer for a UIView when you are attempting to display a view or layer that exceeds the maximum texture size supported by the GPU. Apple lists this as 1024x1024 for the iPhone, but in my experience I've been able to go up to 2048x2048 on even the first-generation iPhone.
If you are able to render to a view or layer that is smaller in both width and height than those dimensions, you don't need to use a CATiledLayer and can get away with a standard layer. The tiling process does slow rendering a bit as it brings in the appropriate tiles, so you could gain some performance that way.
For a discussion on general PDF rendering performance, I direct you to this question:
Fast and Lean PDF Viewer for iPhone / iPad / iOs - tips and hints?