利用helixtoolkit实现鼠标拖拽模型（不附加操作器）

思路&步骤

大致思想就是利用viewport场景中，相机的方向与模型所在点确定模型的移动平面。再将鼠标在屏幕上的2d坐标转换成viewport中的3d坐标，确定模型新的位置。

1. 鼠标按下时，先拿到模型visual
2. 鼠标移动时，将鼠标的二维坐标转换成viewport场景中的射线
3. 得到射线与移动平面的交点，并以该交点作为模型的新位置
4. 使用Transform更新模型位置

代码实现

前台：

 1 <Window
 2     x:Class="MouseDrag.MainWindow"
 3     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
 4     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
 5     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
 6     xmlns:helix="http://helix-toolkit.org/wpf"
 7     xmlns:local="clr-namespace:MouseDrag"
 8     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
 9     Title="MainWindow"
10     Width="800"
11     Height="450"
12     mc:Ignorable="d">
13     <Grid>
14         <helix:HelixViewport3D
15             x:Name="view"
16             Background="LightGray"
17             Camera="{helix:PerspectiveCamera 43.11,
18                                              -74.67,
19                                              49.78}"
20             MouseDown="view_MouseDown"
21             MouseMove="view_MouseMove"
22             ShowCameraInfo="True"
23             ShowCoordinateSystem="True">
24             <helix:GridLinesVisual3D />
25             <helix:DefaultLights />
26             <helix:CubeVisual3D x:Name="cube" SideLength="10" />
27         </helix:HelixViewport3D>
28     </Grid>
29 </Window>

后台：

 1 using HelixToolkit.Wpf;
 2 using System.Windows;
 3 using System.Windows.Input;
 4 using System.Windows.Media.Media3D;
 5 
 6 namespace MouseDrag
 7 {
 8     /// <summary>
 9     /// MainWindow.xaml 的交互逻辑
10     /// </summary>
11     public partial class MainWindow : Window
12     {
13         CubeVisual3D selectCube = new CubeVisual3D();
14 
15         public MainWindow()
16         {
17             InitializeComponent();
18                         cube2.Transform = new TranslateTransform3D(20, 0, 0);
19         }
20 
21         private void view_MouseDown(object sender, MouseButtonEventArgs e)
22         {
23             Visual3D visual = view.FindNearestVisual(e.GetPosition(view));
24             if(visual != null && visual is CubeVisual3D)
25             {
26                 selectCube = visual as CubeVisual3D;//捕获按下的visual
27             }
28         }
29         private void view_MouseMove(object sender, MouseEventArgs e)
30         {
31             if (e.LeftButton == MouseButtonState.Pressed)
32             {
33                 Matrix3D mat = cube.Transform.Value;//模型的变换矩阵
34                 Vector3D lookdirction = view.Camera.LookDirection;//相机方向
35                 Point3D dot = new Point3D(mat.OffsetX, mat.OffsetY, mat.OffsetZ);//模型位置
36 
37                 Ray3D ray = Viewport3DHelper.Point2DtoRay3D(view.Viewport, e.GetPosition(view));//射线类
38                 var point = ray.PlaneIntersection(dot, lookdirction);//移动平面上的交点
39 
40                 mat.OffsetX = ((Point3D)point).X;
41                 mat.OffsetY = ((Point3D)point).Y;
42                 mat.OffsetZ = ((Point3D)point).Z;
43 
44                 Transform3D trans = new MatrixTransform3D(mat);
45                 cube.Transform = trans;
46             }
47         }
48     }
49 }

效果