Custom multiple point function. \n
* Source values are copies, so they can be changed inside the function without affecting the original image. \n
* Data will be set only if the returned value is non zero.
* \verbatim func(src_value1: number, src_value2: number, ... , params1, param2, ..., x: number, y: number, d: number) -> dst_value: number [in Lua 5] \endverbatim
* In Lua, the source images data and the params table are 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 multiple point function. \n * Source values are copies, so they can be changed inside the function without affecting the original image. \n * Data will be set only if the returned value is non zero. * \verbatim func(src_value1: number, src_value2: number, ... , params1, param2, ..., x: number, y: number, d: number) -> dst_value: number [in Lua 5] \endverbatim * In Lua, the source images data and the params table are unpacked. * And the returned value contains only the target values to update, or nil (also no return value) to leave target intact. * \ingroup point