Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Camera
MGCAMERASHADER_LINK
Parameter: Horizontal Scale
MGCAMERASHADER_HSCALE
Parameter: Vertical Scale
MGCAMERASHADER_VSCALE
Parameter: Include Foreground
MGCAMERASHADER_CALC_FG
Parameter: Include Background
MGCAMERASHADER_CALC_BG