Reference for unit 'fpg_extinterpolation'

Extra interpolation filter declarations.

`uses`
`System,`
`Classes,`
`SysUtils,`
`fpg_base;`		The base unit and starting point of fpGUI

Overview

Some more interpolation filters for TfpgCanvasBase.StretchDraw:
Bessel, Gaussian and Sinc are infinite impulse response (IIR), the others are finite impulse response (FIR). The implementation of Bessel and Sinc are windowed with Blackman filter.

This unit was ported from fcl-image which is part of FPC. A few more filters have also been added.