C# 開發 WPF/Silverlight 動畫與遊戲系列教程（二）讓物體動起來 ②（一）—— CompositionTarget 幀動畫實作

CompositionTarget 動畫原理

官方描述：CompositionTarget 依每幀回調創建自訂動畫。實際上基於每次介面重繪觸發，與視窗重繪率同步，頻率固定難人工干預。

完整實作代碼

Rectangle rect;
double speed = 1;
Point moveTo;

public Window1() {
    InitializeComponent();
    rect = new Rectangle();
    rect.Fill = new SolidColorBrush(Colors.Red);
    rect.Width = 50;
    rect.Height = 50;
    rect.RadiusX = 5;
    rect.RadiusY = 5;
    Carrier.Children.Add(rect);
    Canvas.SetLeft(rect, 0);
    Canvas.SetTop(rect, 0);
    CompositionTarget.Rendering += new EventHandler(Timer_Tick);
}

private void Carrier_MouseLeftButtonDown(object sender, MouseButtonEventArgs e) {
    moveTo = e.GetPosition(Carrier);
}

private void Timer_Tick(object sender, EventArgs e) {
    double rect_X = Canvas.GetLeft(rect);
    double rect_Y = Canvas.GetTop(rect);
    Canvas.SetLeft(rect, rect_X + (rect_X < moveTo.X ? speed : -speed));
    Canvas.SetTop(rect, rect_Y + (rect_Y < moveTo.Y ? speed : -speed));
}

註冊事件：CompositionTarget.Rendering += new EventHandler(Timer_Tick);
滑鼠點擊記錄目標點 moveTo，X、Y 速度同設為 speed。
Timer_Tick 為重繪回調，每幀更新位置趨近目標。