[Enhancement] DeviceDisplay/DisplayInfo should report refresh rate

[janusw]

Summary

DisplayInfo already contains various information about the display, like width/height, density, orientation, rotation, etc. It should also include the device's screen refresh rate.

API Changes

The DisplayInfo struct should obtain a new property called RefreshRate or similar:

public readonly struct DisplayInfo : IEquatable<DisplayInfo>
{
    [...]
    public double RefreshRate { get; }
    [...]
}

Example usage:

// Get Metrics
var mainDisplayInfo = DeviceDisplay.MainDisplayInfo;

// display refresh rate in Hz (i.e. "frames per second")
var rate = mainDisplayInfo.RefreshRate;

Intended Use Case

The refresh rate can be useful for example in connection with sensor update rates, which are configurable via SensorSpeed (or can be throttled manually). If one knows the screen refresh rate, one can make sharper constraints on the necessary sensor rates. E.g. if my screen updates only with 30 Hz, I probably don't need to sample the OrientationSensor with 50 Hz, because the information can not be displayed that quickly. Or the other way around: If I know that my screen updates with 60 or even 120 Hz, then I might want to increase the sensor updates accordingly, so that I can get a smoother display (e.g. think of an "augmented-reality"-type camera overlay).

Implementation

Some pointers that might be useful for the implementation:

• Android: https://docs.microsoft.com/en-us/dotnet/api/android.views.display.refreshrate
• iOS: https://developer.apple.com/documentation/uikit/uiscreen/2806814-maximumframespersecond

[janusw]

Getting the refresh rate on iOS and Android seems to be straightforward, but I did not find a way to obtain it on MacOS :(

The class AppKit.NSScreen, which is already being used in DeviceDisplay.macos.cs does not seem to provide anything in this direction: https://developer.apple.com/documentation/appkit/nsscreen

In principle there is a CGDisplayMode.refreshRate in Apple's CoreGraphics for MacOS: https://developer.apple.com/documentation/coregraphics/cgdisplaymode/1454661-refreshrate

However, in the .NET APIs for Xamarin.Mac, I only find a CGDisplay class, but no way to get a fresh rate or even just a CGDisplayMode.

[janusw]

In principle there is a CGDisplayMode.refreshRate in Apple's CoreGraphics for MacOS: https://developer.apple.com/documentation/coregraphics/cgdisplaymode/1454661-refreshrate

However, in the .NET APIs for Xamarin.Mac, I only find a CGDisplay class, but no way to get a fresh rate or even just a CGDisplayMode.

Maybe one should open a feature request in https://github.com/xamarin/xamarin-macios (or am I just missing something)?

[janusw]

Maybe one should open a feature request in https://github.com/xamarin/xamarin-macios (or am I just missing something)?

Just did that: xamarin/xamarin-macios#9958

[janusw]

Finally, the following might be relevant for an UWP implementation: https://docs.microsoft.com/en-us/uwp/api/windows.graphics.display.core.hdmidisplaymode.refreshrate

[mattleibow]

Thanks for all the work and research on this one!