Vertex Cube旋转中心

Question

如何找到使用顶点缓冲区制作的立方体的旋转中心？ 立方体当前正在一个顶点上旋转，我整个星期都在试图弄清楚如何将它调整到中心。

这里是我的渲染立方体代码：

class RenderCube 
{ 

    KeyboardState currentKeys; 
    GamePadState currentGamepad; 

    //Transform later to have static v and i buffers. 
    private VertexBuffer vBuffer; 
    public VertexBuffer VBuffer 
    { get { return vBuffer; } set { vBuffer = value; } } 

    private IndexBuffer iBuffer; 
    public IndexBuffer IBuffer 
    { get { return iBuffer; } set { iBuffer = value; } } 

    private BasicEffect bEffect; 
    public BasicEffect BEffect 
    { get { return bEffect; } set { bEffect = value; } } 

    private Matrix world; 
    public Matrix World 
    { get { return world; } set { world = value; } } 

    private Matrix view; 
    public Matrix View 
    { get { return view; } set { view = value; } } 

    private Matrix projection; 
    private Matrix Projection 
    { get { return projection; } set { projection = value; } } 

    private Color color; 
    public Color Color 
    { get { return color; } set { color = value; } } 

    private Vector3 position; 
    public Vector3 Position 
    { get { return position; } set { position = value; } } 

    //Need to change this eventually to use textures. 
    private VertexPositionColor[] vertices; 
    short[] indices; 


    private GraphicsDevice device; 
    //constructors! 
    public RenderCube(Color col, Vector3 pos, GraphicsDevice dev) 
    { 
     device = dev; 

     this.color = col; 
     this.position = pos; 
     SetUpVertices(); 
     SetUpIndices(); 

     world = Matrix.CreateTranslation(position); 
     //world = Matrix.CreateTranslation(0, 0, 0); 
     bEffect = new BasicEffect(device); 
     bEffect.World = world; 
     bEffect.VertexColorEnabled = true; 
     //bEffect.EnableDefaultLighting(); 
    } 

    public void Render(Camera cam) 
    { 
     bEffect.View = cam.view; 
     bEffect.Projection = cam.projection; 
     bEffect.World *= cam.rotX; 
     bEffect.World *= cam.rotY; 
     bEffect.World *= cam.rotZ; 

     var rotationCenter = new Vector3(0.5f, 0.5f, 0.5f); 

     device.SetVertexBuffer(vBuffer); 
     device.Indices = IBuffer; 

     foreach (EffectPass pass in bEffect.CurrentTechnique.Passes) 
     { 
      pass.Apply(); 
      device.DrawIndexedPrimitives(PrimitiveType.TriangleList, 0, 0, 8, 0, 12); 
     } 
    } 

    /// <summary> 
    /// Sets up the vertices for a cube using 8 unique vertices. 
    /// Build order is front to back, left to up to right to down. 
    /// </summary> 
    private void SetUpVertices() 
    { 
     vertices = new VertexPositionColor[8]; 

     //front left bottom corner 
     vertices[0] = new VertexPositionColor(new Vector3(0, 0, 0), color); 
     //front left upper corner 
     vertices[1] = new VertexPositionColor(new Vector3(0, 100, 0), color); 
     //front right upper corner 
     vertices[2] = new VertexPositionColor(new Vector3(100, 100, 0), color); 
     //front lower right corner 
     vertices[3] = new VertexPositionColor(new Vector3(100, 0, 0), color); 
     //back left lower corner 
     vertices[4] = new VertexPositionColor(new Vector3(0, 0, -100), color); 
     //back left upper corner 
     vertices[5] = new VertexPositionColor(new Vector3(0, 100, -100), color); 
     //back right upper corner 
     vertices[6] = new VertexPositionColor(new Vector3(100, 100, -100), color); 
     //back right lower corner 
     vertices[7] = new VertexPositionColor(new Vector3(100, 0, -100), color); 

     vBuffer = new VertexBuffer(device, typeof(VertexPositionColor), 8, BufferUsage.WriteOnly); 
     vBuffer.SetData<VertexPositionColor>(vertices); 
    } 

    /// <summary> 
    /// Sets up the indices for a cube. Has 36 positions that match up 
    /// to the element numbers of the vertices created earlier. 
    /// Valid range is 0-7 for each value. 
    /// </summary> 
    private void SetUpIndices() 
    { 
     indices = new short[36]; 

     //Front face 
     //bottom right triangle 
     indices[0] = 0; 
     indices[1] = 3; 
     indices[2] = 2; 
     //top left triangle 
     indices[3] = 2; 
     indices[4] = 1; 
     indices[5] = 0; 
     //back face 
     //bottom right triangle 
     indices[6] = 4; 
     indices[7] = 7; 
     indices[8] = 6; 
     //top left triangle 
     indices[9] = 6; 
     indices[10] = 5; 
     indices[11] = 4; 
     //Top face 
     //bottom right triangle 
     indices[12] = 1; 
     indices[13] = 2; 
     indices[14] = 6; 
     //top left triangle 
     indices[15] = 6; 
     indices[16] = 5; 
     indices[17] = 1; 
     //bottom face 
     //bottom right triangle 
     indices[18] = 4; 
     indices[19] = 7; 
     indices[20] = 3; 
     //top left triangle 
     indices[21] = 3; 
     indices[22] = 0; 
     indices[23] = 4; 
     //left face 
     //bottom right triangle 
     indices[24] = 4; 
     indices[25] = 0; 
     indices[26] = 1; 
     //top left triangle 
     indices[27] = 1; 
     indices[28] = 5; 
     indices[29] = 4; 
     //right face 
     //bottom right triangle 
     indices[30] = 3; 
     indices[31] = 7; 
     indices[32] = 6; 
     //top left triangle 
     indices[33] = 6; 
     indices[34] = 2; 
     indices[35] = 3; 

     iBuffer = new IndexBuffer(device, IndexElementSize.SixteenBits, sizeof(short) * indices.Length, BufferUsage.WriteOnly); 
     iBuffer.SetData(indices); 
    } 
} 

Answer 1

的基本思路是引入推动立方体原点的平移矩阵，进行旋转和撤消转换：

public void Render(Camera cam) 
{ 
    //... 
    //push the cube to the origin 
    bEffect.World *= Matrix.CreateTranslation(-50, -50, 50); 
    //perform the rotation 
    bEffect.World *= cam.rotX; 
    bEffect.World *= cam.rotY; 
    bEffect.World *= cam.rotZ; 
    //undo the translation 
    bEffect.World *= Matrix.CreateTranslation(50, 50, -50); 
    //...