maui-linux/Xamarin.Forms.Platform.GTK/Animations/BaseAnimation.cs

using System;
using System.Threading.Tasks;
using System.Timers;

namespace Xamarin.Forms.Platform.GTK.Animations
{
	internal abstract class BaseAnimation
	{
		private const double AnimationInterval = 1000 / 60.0;

		private TimeSpan _totalTime;
		private Task _animTask;
		private Timer _timer;
		private DateTime _startTime;
		private bool _isEased;
		private double _elapsed;
		private double _lerp;

		public BaseAnimation(TimeSpan time, bool isEased)
		{
			_totalTime = time;
			_isEased = isEased;

			_timer = new Timer();
			_timer.Interval = AnimationInterval;
			_timer.Elapsed += OnTimerElapsed;
		}

		protected abstract void AnimationStep(double lerp);

		private void OnTimerElapsed(object sender, ElapsedEventArgs e)
		{
			_elapsed = (e.SignalTime - _startTime).TotalMilliseconds;

			_lerp = _elapsed / _totalTime.TotalMilliseconds;

			if (_isEased)
			{
				_lerp = SmoothLerp(0, 1, (float)_lerp);
			}

			AnimationStep(_lerp);
		}

		protected static float SmoothLerp(float value1, float value2, float amount)
		{
			float num = Clamp(amount, 0f, 1f);

			return Lerp(value1, value2, (num * num) * (3f - (2f * num)));
		}

		protected static float Clamp(float value, float min, float max)
		{
			value = (value > max) ? max : value;
			value = (value < min) ? min : value;

			return value;
		}

		protected static float Lerp(float value1, float value2, float amount)
		{
			return value1 + ((value2 - value1) * amount);
		}

		public async Task Run()
		{
			if (_animTask != null)
			{
				// TODO: Cancel or throw exception
			}

			_startTime = DateTime.Now;
			_timer.Start();
			_animTask = Task.Delay(_totalTime);
			await _animTask;

			if (_animTask.Status == TaskStatus.RanToCompletion)
			{
				_timer.Stop();

				AnimationStep(1);
			}

			_animTask = null;
		}
	}
}