作圆问题，求改修，指导
求助各位大神，为何不能准确的拖拽出圆，是算法有问题么？
（需求，按下屏幕时是中心点，拖拽，当松开的时候是第二个点。以中心点到第二个点为半径作圆）
using System;using System.Collections.Generic;using System.Linq;using System.Net;using System.Windows;using System.Windows.Controls;using System.Windows.Documents;using System.Windows.Input;using System.Windows.Media;using System.Windows.Media.Animation;using System.Windows.Shapes;using Microsoft.Phone.Controls;namespace Shape_draw_Circle{ public partial class MainPage : PhoneApplicationPage { // 构造函数 Random rand = new Random(); bool isDrawing, isDragging; Path path; EllipseGeometry ellipseGeo; public MainPage() { InitializeComponent(); } protected override void OnManipulationStarted(ManipulationStartedEventArgs args) { if (isDrawing || isDragging) { return; } if (args.OriginalSource is Path) { ellipseGeo = (args.OriginalSource as Path).Data as EllipseGeometry; isDragging = true; args.ManipulationContainer = ContentPanel; args.Handled = true; } else if (args.OriginalSource == ContentPanel) { ellipseGeo = new EllipseGeometry(); ellipseGeo.Center = args.ManipulationOrigin; path = new Path(); path.Stroke = this.Resources["PhoneForegroundBrush"] as Brush; path.Data = ellipseGeo; ContentPanel.Children.Add(path); isDrawing = true; args.Handled = true; } base.OnManipulationStarted(args); } protected override void OnManipulationDelta(ManipulationDeltaEventArgs args) { if (isDragging) { Point center = ellipseGeo.Center; center.X += args.DeltaManipulation.Translation.X; center.Y += args.DeltaManipulation.Translation.Y; args.Handled = true; } else if (isDrawing) { Point translation = args.CumulativeManipulation.Translation; //double radius = Math.Max(Math.Abs(translation.X), // Math.Abs(translation.Y)); //ellipseGeo.RadiusX = radius; //ellipseGeo.RadiusY = radius; //BY YZX //Math.Sqrt 开根 //Math.Pow 求幂 //radius 求圆的半径 double radius =Math.Sqrt(Math.Pow((translation.X - ellipseGeo.Center.X),2)+Math.Pow((translation.Y - ellipseGeo.Center.Y),2)); ellipseGeo.RadiusX = radius; ellipseGeo.RadiusY = radius; args.Handled = true; } base.OnManipulationDelta(args); } protected override void OnManipulationCompleted(ManipulationCompletedEventArgs args) { if (isDragging) { isDragging = false; args.Handled = true; } else if (isDrawing) { Color clr = Color.FromArgb(255, 0, 0, 0); Color clr2 = Color.FromArgb(255, 5, 5, 5); //path.Fill = new SolidColorBrush(clr); path.Stroke = new SolidColorBrush(clr2); path.StrokeThickness = 10; isDrawing = false; args.Handled = true; } base.OnManipulationCompleted(args); } }}