如何在silverlight 5 3D中绘制透明立方体？

Question

我使用以下代码生成我的3D立方体，但它不会产生透明的立方体。任何帮助都将受到赞赏。

VertexBuffer CreateCube(GraphicsDevice device)
{
    var vertexCollection = new VertexPositionColor[36];

    // Front coordinates
    Vector3 cubeA = new Vector3(-0.75f, 0.75f, 0.75f);
    Vector3 cubeB = new Vector3(0.75f, 0.75f, 0.75f);
    Vector3 cubeC = new Vector3(-0.75f, -0.75f, 0.75f);
    Vector3 cubeD = new Vector3(0.75f, -0.75f, 0.75f);

    // Back coordinates
    Vector3 cubeE = new Vector3(-0.75f, 0.75f, -0.75f);
    Vector3 cubeF = new Vector3(0.75f, 0.75f, -0.75f);
    Vector3 cubeG = new Vector3(-0.75f, -0.75f, -0.75f);
    Vector3 cubeH = new Vector3(0.75f, -0.75f, -0.75f);

    // Colors
    Color cRed = Color.FromNonPremultiplied(255, 0, 0, 156);
    //Color cred = new Color(new Vector4(255,0,0,150));

    Color cGreen = Color.FromNonPremultiplied(0, 255, 0, 156);
    Color cBlue = Color.FromNonPremultiplied(0, 0, 255, 156);
    Color cYellow = Color.FromNonPremultiplied(255, 255, 0, 156);
    Color cBlack = Color.FromNonPremultiplied(0, 0, 0, 156);
    Color cWhite = Color.FromNonPremultiplied(255, 255, 255, 156);

    // Front
    vertexCollection[0] = new VertexPositionColor(cubeA, cGreen);
    vertexCollection[1] = new VertexPositionColor(cubeB, cGreen);
    vertexCollection[2] = new VertexPositionColor(cubeC, cGreen);
    vertexCollection[3] = new VertexPositionColor(cubeB, cBlue);
    vertexCollection[4] = new VertexPositionColor(cubeD, cBlue);
    vertexCollection[5] = new VertexPositionColor(cubeC, cBlue);

    // Back 
    vertexCollection[6] = new VertexPositionColor(cubeG, cBlue);
    vertexCollection[7] = new VertexPositionColor(cubeF, cBlue);
    vertexCollection[8] = new VertexPositionColor(cubeE, cBlue);
    vertexCollection[9] = new VertexPositionColor(cubeH, cGreen);
    vertexCollection[10] = new VertexPositionColor(cubeF, cGreen);
    vertexCollection[11] = new VertexPositionColor(cubeG, cGreen);

    // Top
    vertexCollection[12] = new VertexPositionColor(cubeE, cRed);
    vertexCollection[13] = new VertexPositionColor(cubeF, cRed);
    vertexCollection[14] = new VertexPositionColor(cubeA, cRed);
    vertexCollection[15] = new VertexPositionColor(cubeF, cYellow);
    vertexCollection[16] = new VertexPositionColor(cubeB, cYellow);
    vertexCollection[17] = new VertexPositionColor(cubeA, cYellow);

    // Bottom 
    vertexCollection[18] = new VertexPositionColor(cubeH, cRed);
    vertexCollection[19] = new VertexPositionColor(cubeG, cRed);
    vertexCollection[20] = new VertexPositionColor(cubeC, cRed);
    vertexCollection[21] = new VertexPositionColor(cubeD, cYellow);
    vertexCollection[22] = new VertexPositionColor(cubeH, cYellow);
    vertexCollection[23] = new VertexPositionColor(cubeC, cYellow);

    // Left
    vertexCollection[24] = new VertexPositionColor(cubeC, cBlack);
    vertexCollection[25] = new VertexPositionColor(cubeG, cBlack);
    vertexCollection[26] = new VertexPositionColor(cubeA, cBlack);
    vertexCollection[27] = new VertexPositionColor(cubeA, cWhite);
    vertexCollection[28] = new VertexPositionColor(cubeG, cWhite);
    vertexCollection[29] = new VertexPositionColor(cubeE, cWhite);

    // Right 
    vertexCollection[30] = new VertexPositionColor(cubeH, cWhite);
    vertexCollection[31] = new VertexPositionColor(cubeD, cWhite);
    vertexCollection[32] = new VertexPositionColor(cubeB, cWhite);
    vertexCollection[33] = new VertexPositionColor(cubeH, cBlack);
    vertexCollection[34] = new VertexPositionColor(cubeB, cBlack);
    vertexCollection[35] = new VertexPositionColor(cubeF, cBlack);

    var vb = new VertexBuffer(device,
        VertexPositionColor.VertexDeclaration,
        vertexCollection.Length, BufferUsage.WriteOnly);
    vb.SetData(0, vertexCollection, 0, vertexCollection.Length, 0);

    return vb;
}