Function IODisplayGetFloatParameter 

pub unsafe extern "C-unwind" fn IODisplayGetFloatParameter(
    service: io_service_t,
    options: IOOptionBits,
    parameter_name: Option<&CFString>,
    value: *mut c_float,
) -> IOReturn

Available on crate features graphics and libc only.

Safety

• parameter_name might not allow None.
• value must be a valid pointer.