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// Copyright 2018, The Gtk-rs Project Developers.
// See the COPYRIGHT file at the top-level directory of this distribution.
// Licensed under the MIT license, see the LICENSE file or <http://opensource.org/licenses/MIT>

use gdk_sys;
use glib::translate::*;
use std::num::NonZeroU64;
use FrameTimings;

impl FrameTimings {
    /// Gets the predicted time at which this frame will be displayed. Although
    /// no predicted time may be available, if one is available, it will
    /// be available while the frame is being generated, in contrast to
    /// `FrameTimings::get_presentation_time`, which is only available
    /// after the frame has been presented. In general, if you are simply
    /// animating, you should use `FrameClock::get_frame_time` rather
    /// than this function, but this function is useful for applications
    /// that want exact control over latency. For example, a movie player
    /// may want this information for Audio/Video synchronization.
    ///
    /// # Returns
    ///
    /// The predicted time at which the frame will be presented,
    ///  in the timescale of `g_get_monotonic_time`, or 0 if no predicted
    ///  presentation time is available.
    pub fn get_predicted_presentation_time(&self) -> Option<NonZeroU64> {
        let predicted_presentation_time = unsafe {
            gdk_sys::gdk_frame_timings_get_predicted_presentation_time(self.to_glib_none().0)
        };
        // assuming presentation time is always positive
        assert!(predicted_presentation_time >= 0);
        // `0` means the value is not available
        NonZeroU64::new(predicted_presentation_time as u64)
    }

    /// Reurns the presentation time. This is the time at which the frame
    /// became visible to the user.
    ///
    /// # Returns
    ///
    /// the time the frame was displayed to the user, in the
    ///  timescale of `g_get_monotonic_time`, or 0 if no presentation
    ///  time is available. See `FrameTimings::get_complete`
    pub fn get_presentation_time(&self) -> Option<NonZeroU64> {
        let presentation_time =
            unsafe { gdk_sys::gdk_frame_timings_get_presentation_time(self.to_glib_none().0) };
        // assuming presentation time is always positive
        assert!(presentation_time >= 0);
        // `0` means the value is not available
        NonZeroU64::new(presentation_time as u64)
    }

    /// Gets the natural interval between presentation times for
    /// the display that this frame was displayed on. Frame presentation
    /// usually happens during the “vertical blanking interval”.
    ///
    /// # Returns
    ///
    /// the refresh interval of the display, in microseconds,
    ///  or 0 if the refresh interval is not available.
    ///  See `FrameTimings::get_complete`.
    pub fn get_refresh_interval(&self) -> Option<NonZeroU64> {
        let refresh_interval =
            unsafe { gdk_sys::gdk_frame_timings_get_refresh_interval(self.to_glib_none().0) };
        // assuming refresh interval is always positive
        assert!(refresh_interval >= 0);
        // `0` means the value is not available
        NonZeroU64::new(refresh_interval as u64)
    }
}