delphi - 在 GLScene 中抓取鼠标位置下的顶点

Question

我正在使用 GLScene 编写一个 3D 建模应用程序，因此我需要通过抓取顶点将鼠标位置下的一些顶点移动到新位置。首先，我加载一个球体并用鼠标拾取一个顶点，然后尝试拖动它，但我意识到该顶点没有在鼠标插入符下正确移动。

    unit Unit1;

    interface

    uses
      Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
      Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Math,
      //GLScene
      GLWin32Viewer, GLCrossPlatform, GLBaseClasses, GLScene, GLColor, GLCanvas,
      GLVectorFileObjects, GLObjects,GLVectorTypes,
      GLCoordinates, GLFileObj, GLVectorGeometry;

    type
      TForm1 = class(TForm)
        GLSceneViewer: TGLSceneViewer;
        GLScene1: TGLScene;
        GLLightSource1: TGLLightSource;
        GLCamera: TGLCamera;
        GLDummyCube1: TGLDummyCube;
        FreeForm: TGLFreeForm;
        GLLightSource2: TGLLightSource;
        procedure FormCreate(Sender: TObject);
        procedure GLSceneViewerMouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
        procedure GLSceneViewerMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
        procedure GLSceneViewerMouseUp(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
        procedure GLSceneViewerPostRender(Sender: TObject);
      private
        { Private declarations }
        IsVertexDragging: Boolean;

        MouseX, MouseY : Integer;
        VertexIndexToDrag: Integer;
        CenterPosition, LastPosition: TVector3f;
        function FindClosestPointIndex(Point: TVector3f): Integer;

      public
        { Public declarations }
      end;

    var
      Form1: TForm1;

    implementation

    {$R *.dfm}

    procedure TForm1.FormCreate(Sender: TObject);
    begin
      FreeForm.LoadFromFile('E:\test2\Sphere.obj');
    end;

    function TForm1.FindClosestPointIndex( Point: TVector3f ): Integer;
    var
      i: Integer;
      NewPoint : TVector3f;
      BestDistance,
      TempDistance: Single;
    begin
      // Search the nearest point between  all vertices in the sphere.
      BestDistance := 100000000000000;
      for i:=0 to FreeForm.MeshObjects[0].Vertices.Count-1 do
      begin

          NewPoint := FreeForm.MeshObjects[0].Vertices[i];
          TempDistance := VectorDistance( Point, NewPoint );

          if TempDistance <= BestDistance  then
          begin
            BestDistance := TempDistance;
            Result := i;
          end;
      end;

    end;

    procedure TForm1.GLSceneViewerMouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
    var
      Vertex: TVector3f;
    begin

      MouseX := X;
      MouseY := Y;

      if (ssLeft in Shift) and not (ssCtrl in Shift) then
      begin
        IsVertexDragging := True;

        Vertex := GLSceneViewer.Buffer.PixelRayToWorld( X, Y );
        Vertex := FreeForm.AbsoluteToLocal(Vertex);

        // Find closest point to the mouse click position
        VertexIndexToDrag := FindClosestPointIndex( Vertex );
        //start of dragging position.
        CenterPosition := GLSceneViewer.Buffer.ScreenToWorld(X,Y);

      end;
    end;

    procedure TForm1.GLSceneViewerMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
    var
      delta: TVector3f;
      i: Integer;
    begin
      if (ssLeft in Shift) and (ssCtrl in Shift) then // Rotating camera
        GLCamera.MoveAroundTarget(0.5*(MouseY-Y), 0.5*(MouseX-X) )
      else
      if (ssLeft in Shift) and not (ssCtrl in Shift) and IsVertexDragging then
      begin // Dragging vertex

        LastPosition := GLSceneViewer.Buffer.ScreenToWorld(X,Y);

        delta.X := RoundTo( LastPosition.X - CenterPosition.X, -5 );
        delta.Y := RoundTo( LastPosition.Y - CenterPosition.Y, -5 );
        delta.Z := RoundTo( LastPosition.Z - CenterPosition.Z, -5 );

        Caption := delta.Z.ToString;
        CenterPosition := LastPosition;

        FreeForm.MeshObjects[0].Vertices.TranslateItem( VertexIndexToDrag , Delta );

        FreeForm.TransformationChanged;
      end;

      MouseX := X;
      MouseY := Y;

    end;

    procedure TForm1.GLSceneViewerMouseUp(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    begin
      IsVertexDragging := False;
    end;

    procedure TForm1.GLSceneViewerPostRender(Sender: TObject);
    var
      glc: TGLCanvas;
    begin
      // Show a circle with mouse position
      if IsVertexDragging then
      begin
        glc := TGLCanvas.Create( GLSceneViewer.Width, GLSceneViewer.Height );
        glc.PenWidth := 2;
        glc.PenColor := clLime;
        glc.Ellipse( MouseX, MouseY, 5, 5 );
        glc.Free;
      end;
      GLSceneViewer.Invalidate;

    end;

    end.

我这是怎么了？我想写一个类似 stephaneginier.com/sculptgl 的工具

Answer 1

解决这个问题的一种方法是解决以下问题 line-plane intersection :

沿着l、d的距离可以这样找到:

交点为

您现在需要的只是输入。我从未使用过 GLScene，所以这只是为您指明正确的方向:

• 正常的n是camera's forward direction, GLCamera.Direction .

• 平面上的点，p_0 是 LocalToAbsolute(Vertex)

• 光线起点 l_0 可以是相机的位置 GLCamera.Position 或近平面上的点 GLSceneViewer.Buffer。 ScreenToWorld(x, y).

• 光线方向，l，是投影的鼠标方向，GLSceneViewer.Buffer.ScreenToVector(x, y)

最后，您需要使用 AbsoluteToLocal 将交点放回对象空间。

看起来这个相交测试可能有捷径(例如使用来自PixelRayToWorld的光线)，但就像我说的我不知道GLScene。