silverlight图片局部放大效果

很多购物平台中(比如京东购物)，浏览产品详情时都有这种效果，前几天看到有朋友问SL能不能实现，当然可以

界面:

1.左侧小图片(用一个矩形Fill一张图片即可)
2.左侧半透明矩形
3.右侧大图片(用一个Canvas设置Clip裁剪可视区域作为蒙板，图片放置在Canvas中即可)

原理：

获取左侧半透明矩形的相对位置，然后动态调整右侧大图的Canvas.Left与Canvas.Top

需要知道以下技术点:
1.Clip的应用
2.如何拖动对象
3.拖动时的边界检测
4.动态调整对象的Canvas.Left与Canvas.Top属性

尺寸要点:

1.右侧大图可视区域与左侧半透明矩形的“长宽比例”应该相同
2.“图片原始尺寸长度比” 应该 “与左侧小图片长度比”相同
3.图片原始大小/左侧小图大小 = 右侧可视区域大小/半透明矩形大小

关键代码：

代码:by 菩提树下的杨过 http://www.cnblogs.com/yjmyzz

using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;

namespace PartMagnifier
{
     public partial class MainPage : UserControl
    {
         bool trackingMouseMove = false ;
        Point mousePosition;

         public MainPage()
        {
             // 为初始化变量所必需
            InitializeComponent();

        }

         private void LayoutRoot_Loaded( object sender, System.Windows.RoutedEventArgs e)
        {
            Adjust();
        }

         private void Rectangle_MouseLeftButtonDown( object sender, MouseButtonEventArgs e)
        {
            FrameworkElement element = sender as FrameworkElement;
            mousePosition = e.GetPosition(element);
            trackingMouseMove = true ;
             if ( null != element)
            {
                element.CaptureMouse();
                element.Cursor = Cursors.Hand;
            }
            Adjust();
            Debug();
            sb.Begin(); // 标题动画，可去掉
        }

         private void Rectangle_MouseMove( object sender, MouseEventArgs e)
        {
            FrameworkElement element = sender as FrameworkElement;
             if (trackingMouseMove)
            {
                 double deltaV = e.GetPosition(element).Y - mousePosition.Y;
                 double deltaH = e.GetPosition(element).X - mousePosition.X;
                 double newTop = deltaV + ( double )element.GetValue(Canvas.TopProperty);
                 double newLeft = deltaH + ( double )element.GetValue(Canvas.LeftProperty);
                 if (newLeft <= 10 )
                {
                    newLeft = 10 ;
                }
                 if (newLeft >= 130 )
                {
                    newLeft = 130 ;
                }
                 if (newTop <= 10 ) { newTop = 10 ; }
                 if (newTop >= 85 ) { newTop = 85 ; }
                element.SetValue(Canvas.TopProperty, newTop);
                element.SetValue(Canvas.LeftProperty, newLeft);
                mousePosition = e.GetPosition(element);
                Adjust();
                 if (mousePosition.X <= 0 || mousePosition.Y <= 0 ) { return ; }
                Debug();
            }
        }

         private void Rectangle_MouseLeftButtonUp( object sender, MouseButtonEventArgs e)
        {
            FrameworkElement element = sender as FrameworkElement;
            trackingMouseMove = false ;
            element.ReleaseMouseCapture();
            mousePosition.X = mousePosition.Y = 0 ;
            element.Cursor = null ;
        }

         /// <summary>
         /// 调试信息
         /// </summary>
         void Debug()
        {
            txtResult.Text = " 鼠标相对坐标： " + mousePosition.ToString() + " \n小框left： " + rect.GetValue(Canvas.LeftProperty) + " ,小框top： " + rect.GetValue(Canvas.TopProperty) + " \n大图left： " + (( double )img.GetValue(Canvas.LeftProperty)).ToString( " F0 " ) + " ,大图right： " + (( double )img.GetValue(Canvas.TopProperty)).ToString( " F0 " );
        }

         /// <summary>
         /// 调整右侧大图的位置
         /// </summary>
         void Adjust()
        {

             double n = cBig.Width / rect.Width;
             double left = ( double )rect.GetValue(Canvas.LeftProperty) - 10 ;
             double top = ( double )rect.GetValue(Canvas.TopProperty) - 10 ;
             double newLeft = - left * n;
             double newTop = - top * n;
            img.SetValue(Canvas.LeftProperty, newLeft);
            img.SetValue(Canvas.TopProperty, newTop);
        }

    }
}

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silverlight图片局部放大效果

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