

So now we know what corners to use in the interpolation, but we now
need to implement the actual filtering. Because we want to implement
this in hardware (which has a bilinear interpolation function builtin), we
seek to find a way to express the 1corner, 2corner, 3corner and 4corner
filtering cases all in terms of a bilinear interpolation function.
The four corner case is trivial, because we see that it's already a
standard bilinear interpolation.
