Custom unary point function. \n
* Data will be set only if the returned value is non zero.
* \verbatim func(src_value: number, params1, param2, ..., x: number, y: number, d: number) -> dst_value: number [in Lua 5] \endverbatim
* In Lua, the params table is unpacked.
* And the returned value contains only the target values to update, or nil (also no return value) to leave target intact.
* \ingroup point
Custom unary point function. \n * Data will be set only if the returned value is non zero. * \verbatim func(src_value: number, params1, param2, ..., x: number, y: number, d: number) -> dst_value: number [in Lua 5] \endverbatim * In Lua, the params table is unpacked. * And the returned value contains only the target values to update, or nil (also no return value) to leave target intact. * \ingroup point