Visualizations with Flare/Prefuse

Recently we were in need of visualizing lots of data in networks. We started with a Javascript based version using RaphaelJS. RaphaelJS uses SVG/VML as the underlying graphics API. Drawing lots of nodes and edges in different shapes and colors worked like a breeze. But we quickly got performance problems when animating the transitions between different states of the network. So we had to look to an alternative technology which is performant enough and pragmatic to use. Reading a lot about Flex and its promising animation capabilities we gave it a try.
Shortly after we stumbled upon Flare/Prefuse and the stunning demos convinced us. It is very easy to use and gives remarkable results in a short time. We integrated it into our web app but suddenly the visualizations weren’t drawn upon startup. Everything went fine when the visualization was ready before the Flex app was fully completed but when the data was visualized after that the edges and nodes weren’t shown. Debugging our app and reading the Flex Sprite API wasn’t much helpful. But one comment in a superclass of all the Flare sprites solved out problem:

Internally, the DirtySprite class maintains a static list of all "dirty" sprites, and redraws each sprite in the list when a Event.RENDER event is issued. Typically, this process is performed automatically. In a few cases, erratic behavior has been observed due to a Flash Player bug that results in RENDER events not being properly issued. As a fallback, the static renderDirty() method can be invoked to manually force each dirty sprite to be redrawn.

These few cases were the default behaviour of our app, so invoking renderDirty solved all our drawing issues. I found no blog entry or hint in the docs and the demos run perfectly since all data is there before the app is shown. So the lesson here is:

  • retest your assumptions (we thought the Flare sprites were all DataSprites and the next superclass is the Flex API Sprite and forgot about the DirtySprite)
  • besides the demos and tutorials/docs read the API docs carefully, often there are implementation/technology specific hints

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