WPF与缓动(二) 正弦与余弦缓动

                                                                           WPF与缓动(二) 正弦与余弦缓动
                                                                                                          周银辉

如果要比二次缓动(请参见WPF与缓动(一) N次缓动)更平缓, 可以使用正弦或余弦缓动.

如果我们用曲线上点的斜率表示速度,可以发现,由0到PI/2,速度逐渐减小,从PI/2到PI速度逐渐增加.
我们可以总结出如下公式

其中位置的改变量相当于Animation中的To与From的差值, t/t(总)相当于animationClock.CurrentProgress.Value, b实际就是From值

参考如下代码:

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Media.Animation;
using System.Windows;

namespace EaseMoveDemo
{
    public class EaseMoveAnimation : DoubleAnimationBase
    {

        public static readonly DependencyProperty FromProperty = DependencyProperty.Register(
            "From", typeof(double?), typeof(EaseMoveAnimation), new PropertyMetadata(null));

        public static readonly DependencyProperty ToProperty = DependencyProperty.Register(
            "To", typeof(double?), typeof(EaseMoveAnimation), new PropertyMetadata(null));

        public double? From
        {
            get
            {
                return (double?)this.GetValue(EaseMoveAnimation.FromProperty);
            }
            set
            {
                this.SetValue(EaseMoveAnimation.FromProperty, value);
            }
        }

        public double? To
        {
            get
            {
                return (double?)this.GetValue(EaseMoveAnimation.ToProperty);
            }
            set
            {
                this.SetValue(EaseMoveAnimation.ToProperty, value);
            }
        }

        //正余弦缓动
        protected override double GetCurrentValueCore(double defaultOriginValue, double defaultDestinationValue, AnimationClock animationClock)
        {
            double from = (this.From==null?defaultDestinationValue:(double)this.From);
            double to = (this.To==null?defaultOriginValue:(double)this.To);
            double delta = to - from;

            //加速
            //return delta * (1 - Math.Cos(Math.PI / 2 * animationClock.CurrentProgress.Value)) + from;

            //减速
            //return delta * Math.Sin(Math.PI / 2 * animationClock.CurrentProgress.Value) + from;

            //先加速,后减速
            return delta/2 * (1 - Math.Cos(Math.PI * animationClock.CurrentProgress.Value)) + from;
            
        }


        protected override System.Windows.Freezable CreateInstanceCore()
        {
            return new EaseMoveAnimation();
        }
    }
}

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