Replace the placeholder temporal blend in the interpolation shader with a
motion-compensated algorithm. This is finally the point where we are actually
using the optical flow information.
For each output pixel the source position on the f0 and f1 grids is recovered
by fixed-point Picard iteration before the samples are blended. The number of
iterations and the relaxation factor are established through empirical testing
on a couple of ad-hoc samples, representing highly uniform and non-uniform
motion respectively.
The approach here is hardly profound, and not meant to be. There are for sure
many more advanced algorithms for doing motion interpolation from optical flow,
and we can happily replace it with, or add, something more advanced once all
the machinery is in place.
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