Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Gradient
XTMASK_GRADIENTParameter: Enable Altitude Masking
XTMASK_ALTITUDE_ENABLEParameter: Min Altitude
XTMASK_ALTITUDE_MINParameter: Max Altitude
XTMASK_ALTITUDE_MAXParameter: Soften Min
XTMASK_ALTITUDE_SOFTEN_MINParameter: Soften Max
XTMASK_ALTITUDE_SOFTEN_MAXParameter: Noise Height
XTMASK_ALTITUDE_NOISE_HEIGHTParameter: Scale
XTMASK_ALTITUDE_NOISE_SCALEParameter: Enable Slope Masking
XTMASK_SLOPE_ENABLEParameter: Min Slope
XTMASK_SLOPE_MINParameter: Max Slope
XTMASK_SLOPE_MAXParameter: Soften Min
XTMASK_SLOPE_SOFTEN_MINParameter: Soften Max
XTMASK_SLOPE_SOFTEN_MAXParameter: Use Bump
XTMASK_SLOPE_USEBUMPParameter: Direction
XTMASK_SLOPE_DIRECTIONParameter: Custom Direction
XTMASK_SLOPE_DIRECTION_CUSTOMParameter: Alternative Blending
XTMASK_SLOPE_ALTERNATIVEBLENDINGParameter: Hardness
XTMASK_SLOPE_ALTERNATIVEBLENDING_HARDNESSParameter: Use Global Coordinates
XTMASK_GLOBALParameter: Invert
XTMASK_INVERT