Implementation of FIR filters (for scanline effect)

[Dave18]

Hi

I'm trying to use the hardware filter to create a scanline effect in FBA.  I don't really know what I'm doing but through luck rather than judgement I've got it working for 2x scaling using the following.

Simple Scanlines
#up_h
  0   0 128   0   0
  0   0 128   0   0
  0   0 128   0   0
  0   0 128   0   0
  0   0 128   0   0
  0   0 128   0   0
  0   0 128   0   0
  0   0 128   0   0
#up_v3
  0   0 128   0   0
  0   0   0   0   0
  0   0   0   0   0
  0   0   0   0   0
  0   0   0   0   0
  0   0   0   0   0
  0   0   0   0   0
  0   0   0   0   0
#up_v5
  0   0 128   0   0
  0   0 128   0   0
  0   0 128   0   0
  0   0 128   0   0
  0   0 128   0   0
  0   0 128   0   0
  0   0 128   0   0
  0   0 128   0   0
 

Unfortunately tis doesn't work for scaling down or non-2x. Is it possible to write a filter that works on both scaling up and down including non-integer scaling?

Thanks

Dave