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A colleague of mine, Pierre Fillard, has just integrated multitouch in the next generation of the VTK-based medical imaging software MedINRIA. The nice thing is that it works on an Apple laptop out of the box.
On his blog, he explain how he did this (warning, it involves C++ and VTK programming). He also gives the code for this! Enjoy.
This reminded me of when the Enthought guys had rigged up a large multitouch screen and wired it in Mayavi for 3D plotting, and in chaco for 2D plotting, using only a web-cam, a video projector, and pure Python image-analysis code: