I'm looking for a raster image drawing software with an "infinite" zoom capability like the image viewer SeaDragon(YouTube-link). Or, alternatively, a library (in any language) with which one could build such a drawing software.
I want to draw images without having to think about resolution, being able to add ("infinite") detail wherever I feel like it.
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Take a look at the piccolo project: http://www.piccolo2d.org/ There is a demo app for drawing which might do what you want, but it's quite easy to make your own. Java + C# versions were pretty good last I checked (last used the Java version about 3 years ago).
I think you might be looking for DeepZoom Composer. There are a number of projects starting up at OpenZoom as well. Although this is relatively new, so the quality is still rather rough.