一、什么是Effect

Effect是WPF特效抽象基类，不可实例化。它的下面有几个子类，分别是DropShadowEffect、BlurEffect和ShaderEffect（抽象子类）。

public abstract class Effect : Animatable, IResource
{
    protected Effect();
    public static Brush ImplicitInput { get; }
    protected internal virtual GeneralTransform EffectMapping { get; }
    public Effect Clone();
    public Effect CloneCurrentValue();

}

从上面的定义得知，Effect 的基类是Animatable，而Animatable是提供动画支持的基类。下面我们介绍一下DropShadowEffect子类。

二、DropShadowEffect阴影特效

DropShadowEffect用于给控件添加阴影效果。。它的定义如下所示：

public sealed class DropShadowEffect : Effect
{
    public static readonly DependencyProperty ShadowDepthProperty;
    public static readonly DependencyProperty ColorProperty;
    public static readonly DependencyProperty DirectionProperty;
    public static readonly DependencyProperty OpacityProperty;
    public static readonly DependencyProperty BlurRadiusProperty;
    public static readonly DependencyProperty RenderingBiasProperty;
 
    public DropShadowEffect();
 
    public double ShadowDepth { get; set; }
    public Color Color { get; set; }
    public double Direction { get; set; }
    public double Opacity { get; set; }
    public double BlurRadius { get; set; }
    public RenderingBias RenderingBias { get; set; }
 
    public DropShadowEffect Clone();
    public DropShadowEffect CloneCurrentValue();
    protected override Freezable CreateInstanceCore();
}

下面是它的常用属性说明表

例如，我们给一个按钮设置阴影效果。

<Button Content="进入WPF中文网" Width="100" Height="50">
    <Button.Effect>
        <DropShadowEffect ShadowDepth="10" BlurRadius="20" Color="Gray"/>
    </Button.Effect>
</Button>

<Window x:Class="HelloWorld.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:HelloWorld" 
        xmlns:controls="clr-namespace:HelloWorld.Controls"
        xmlns:helper="clr-namespace:HelloWorld.MVVM"
        mc:Ignorable="d" 
        Title="WPF中文网 - www.wpfsoft.com" Height="350" Width="500">    
    <Window.DataContext>
        <local:MainViewModel/>
    </Window.DataContext>
    <Grid x:Name="grid" Background="Transparent"
          MouseMove="grid_MouseMove">
        <Button x:Name="button" Content="进入WPF中文网" Width="100" Height="50">
            <Button.Effect>
                <DropShadowEffect Direction="-45" 
                                  ShadowDepth="10" 
                                  BlurRadius="25" 
                                  Color="Gray"/>
            </Button.Effect>
        </Button>
    </Grid>
</Window>

然后在Grid控件的鼠标移动事件中执行以下计算：

private void grid_MouseMove(object sender, MouseEventArgs e)
{
    double width = grid.ActualWidth;
    double height = grid.ActualHeight;
    Point centerPoint = new Point(width / 2, height / 2);
    Point mousePoint = e.GetPosition(grid);
 
    //与X轴的夹角
    double angle = Math.Atan2(
        mousePoint.Y - centerPoint.Y, 
        mousePoint.X - centerPoint.X); //弧度
    double theta = angle * 180 / Math.PI;// 角度
    this.Title = $"角度={theta}";
 
    DropShadowEffect dropShadowEffect = button.Effect as DropShadowEffect;            
 
    //计算距离
    var distance = Math.Sqrt(
        (Math.Pow(mousePoint.X - centerPoint.X, 2) 
        + Math.Pow(mousePoint.Y - centerPoint.Y, 2)));
 
    dropShadowEffect.Direction = -theta;//设置阴影角度
    dropShadowEffect.ShadowDepth = distance/10;//设置阴影偏移量
    dropShadowEffect.BlurRadius = distance / 10 * 2;//设置模糊程度
}

通过这个例子，我们可以直观的感受DropShadowEffect 几个属性值变化所带来的效果。当鼠标在窗体内进行上下左右移动时，按钮的阴影的角度、偏移值和模糊程度都会随之而变化。

当前课程源码下载：（注明：本站所有源代码请按标题搜索）
文件名：098-《DropShadowEffect阴影特效》-源代码
链接：https://pan.baidu.com/s/1yu-q4tUtl0poLVgmcMfgBA
提取码：wpff

——重庆教主 2023年11月9日