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//! Handling of global timestamps.
#[repr(C)]
#[derive(Debug)]
struct MachTimebaseInfo {
numerator: u32,
denominator: u32,
}
extern "C" {
fn mach_timebase_info(out: *mut MachTimebaseInfo) -> u32;
fn mach_absolute_time() -> u64;
}
/// A timer which uses mach_absolute_time to get its time. This is what the metal callbacks use.
#[derive(Debug)]
pub struct PresentationTimer {
scale: MachTimebaseInfo,
}
impl PresentationTimer {
/// Generates a new timer.
pub fn new() -> Self {
// Default to 1 / 1 in case the call to timebase_info fails.
let mut scale = MachTimebaseInfo {
numerator: 1,
denominator: 1,
};
unsafe { mach_timebase_info(&mut scale) };
Self { scale }
}
/// Gets the current time in nanoseconds.
pub fn get_timestamp_ns(&self) -> u128 {
let time = unsafe { mach_absolute_time() };
(time as u128 * self.scale.numerator as u128) / self.scale.denominator as u128
}
}