Displaying an animated graph (= nodes and edges)
Displaying an animated graph (= nodes and edges)
- Subject: Displaying an animated graph (= nodes and edges)
- From: Kaspar Fischer <email@hidden>
- Date: Sun, 16 Aug 2009 12:43:44 +0200
Dear list,
After some hours of research I realise that I need some advice on how
to tackle this: My goal is to render a graph [1] consisting of at most
100 nodes and 300 edges (most of the time the graph will be much
smaller, though). I have an algorithm to position the nodes and the
algorithm works in iterations so that I can use intermediate positions
to animate the placement of the nodes. Ultimately, I want a scrolling
view that allows the user to view the graph and pinch-zoom or double-
tap zoom into it. When zooming in and when the user scrolls, it's okay
if the parts that become visible are initially blurry and will get
redrawn a little later. I need to be able to catch touch events on the
nodes.
I have played around with a UIScrollView and an associated
UIViewController<UIScrollViewDelegate>; the scroll view contains a
custom view that draws the complete graph in its -(void)drawRect:
(CGRect)rect method. I have two problems with this approach: On the
one hand, when the user zoomed in, even though drawRect: is called
again, it draws a blurry graph [2]. On the other hand, I am not sure
how to animate the graph with this approach: I have no layers so I
basically have to do the animation myself and I fear this does not
leverage any of the iPhone's hardware capabilities (layer composition,
etc).
I plan to have a background thread that runs the algorithm and at the
end of each iteration tells the main (UI) thread the new positions of
the nodes.
The questions I have:
1. Would you implement each graph node as a CALayer so that it can
easily be animated, or will that result in too many layers for the
iPhone's Core Animation framework?
2. Should I use UIScrollView? It already provides the scrollbars, the
zooming and panning but I could not remove the blurriness/unsharpness.
I have also come across CATiledLayer but I am not sure whether they
were intended to have sublayers (representing the nodes and edges).
Thanks in advance for any advice on any of these questions!
Kaspar
--
[1] a drawing as you can see on http://en.wikipedia.org/wiki/Graph_(mathematics)
[2] http://halmueller.wordpress.com/2008/10/08/a-very-simple-uiscrollview-demo/
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