This patch implements the Movie Distortion node for the realtime
compositor. The distorted coordinates are computed and cached for a
particular tracking camera distortion parameters. So for expensive
distortion models, the first run will take some time to compute, but
subsequent runs will be fast.
An alternative implementation would be to implement each of the
distortion modes in the shader, but that was decided against for a few
reasons:
1. We want to hide the implementation details of the distortion models,
since it is provided through an external library (Libmv).
2. Some distortion models are expensive to solve accurately, and can be
quite slow to solve each time the shader runs.
3. The typical usage of the node does not involve interactive editing of
the distortion parameters, rather, the parameters are computed during
camera calibration, so caching seems most fitting in that case.
Omar Emara