第01个小程序：随鼠标移动而变色的背景（VaryTheBackground.cs）
程序运行时，当鼠标指针靠近窗口中心程度不同，客户区的背景颜色也不同。
using System;
using System.Windows;
using System.Windows.Input;
using System.Windows.Media;
namespace Chapter02
{
public class VaryTheBackground : Window
{
SolidColorBrush brush = new SolidColorBrush(Colors.Black); //创建画刷 。SolidColorBrush是最简单的画刷。
[STAThread]
public static void Main()
{
Application app = new Application();
app.Run(new VaryTheBackground());
}
public VaryTheBackground()
{
Title = "Vary the Background";
Width = 384;
Height = 384;
Background = brush;
}
//鼠标移动事件
protected override void OnMouseMove(MouseEventArgs args)
{
//窗口呈现尺寸-边框和标题栏的尺寸
double width = ActualWidth
- 2 * SystemParameters.ResizeFrameVerticalBorderWidth;
double height = ActualHeight
- 2 * SystemParameters.ResizeFrameHorizontalBorderHeight
- SystemParameters.CaptionHeight;
Point ptMouse = args.GetPosition(this); //获取鼠标位置
Point ptCenter = new Point(width / 2, height / 2); //窗口中心
Vector vectMouse = ptMouse - ptCenter; //向量。向：中心指向鼠标位置；量：鼠标位置与中心距离
double angle = Math.Atan2(vectMouse.Y, vectMouse.X);
Vector vectEllipse = new Vector(width/ 2 * Math.Cos(angle),
height / 2 * Math.Sin(angle));
Byte byLevel = (byte)(255 * (1 - Math.Min(1, vectMouse.Length / vectEllipse.Length)));
Color clr = brush.Color;
clr.R = clr.G = clr.B = byLevel;
brush.Color = clr;
}
}
}
