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Creating a Custom Vertex Declaration

Demonstrates how to create a custom vertex declaration and use it to render a 3D object.

Bb976065.graphics_custom_vertex(en-us,XNAGameStudio.41).png

Game Studio includes a few predefined classes for common vertex buffer declarations such as VertexPositionColor and VertexPositionColorTexture. If you need to create a vertex buffer declaration that includes additional user-defined types, create a custom vertex declaration.

The Complete Sample

The code in this topic shows you the technique. You can download a complete code sample for this topic, including full source code and any additional supporting files required by the sample.

Creating a Custom Vertex Declaration

A custom vertex declaration is a class that implements fully customizable per-vertex data. Furthermore, if you derive the class from IVertexType, you will not need to create a vertex declaration when creating your vertex buffer or drawing the geometry.

To create a custom vertex declaration

  1. Declare a structure that derives from IVertexType.

    public struct CustomVertex1 : IVertexType
    
  2. Add members to the struct that describe the per-vertex data.

    This example uses position as a Vector3 Structure type, a texture coordinate using a Vector2 Structure type, and a vertex declaration using the VertexDeclaration type.

    Vector3 vertexPosition;
    Vector2 vertexTextureCoordinate;
    
    public readonly static VertexDeclaration VertexDeclaration = new VertexDeclaration
    (
        new VertexElement(0, VertexElementFormat.Vector3, VertexElementUsage.Position, 0),
        new VertexElement(12, VertexElementFormat.Vector2, VertexElementUsage.TextureCoordinate, 0)
    );
    
  3. Implement a constructor and public accessor methods.

    //The constructor for the custom vertex. This allows similar 
    //initialization of custom vertex arrays as compared to arrays of a 
    //standard vertex type, such as VertexPositionColor.
    public CustomVertex1(Vector3 pos, Vector2 textureCoordinate)
    {
        vertexPosition = pos;
        vertexTextureCoordinate = textureCoordinate;
    }
    
    //Public methods for accessing the components of the custom vertex.
    public Vector3 Position
    {
        get { return vertexPosition; }
        set { vertexPosition = value; }
    }
    
    public Vector2 TextureCoordinate
    {
        get { return vertexTextureCoordinate; }
        set { vertexTextureCoordinate = value; }
    }
    
  4. Implement a nonpublic method for accessing the vertex declaration.

    VertexDeclaration IVertexType.VertexDeclaration
    {
        get { return VertexDeclaration; }
    }
    
  5. Create a built-in effect to render the object with a texture using the BasicEffect class as demonstrated in Creating a Basic Effect.

  6. Create the vertex buffer passing in the typeof(CustomVertex1) instead of a vertex declaration to describe the vertex buffer data.

    vertexBuffer = new VertexBuffer(
        graphics.GraphicsDevice,
        typeof(CustomVertex1),
        number_of_vertices,
        BufferUsage.None
        );
    
  7. Create the per-vertex data; this shows a portion of the code.

    Vector3 LeftTopFront = new Vector3(-1.0f, 1.0f, 1.0f);
    Vector3 LeftBottomFront = new Vector3(-1.0f, -1.0f, 1.0f);
    Vector3 LeftTopBack = new Vector3(-1.0f, 1.0f, -1.0f);
    Vector3 LeftBottomBack = new Vector3(-1.0f, -1.0f, -1.0f);
    
    Vector3 RightTopFront = new Vector3(1.0f, 1.0f, 1.0f);
    Vector3 RightBottomFront = new Vector3(1.0f, -1.0f, 1.0f);
    Vector3 RightTopBack = new Vector3(1.0f, 1.0f, -1.0f);
    Vector3 RightBottomBack = new Vector3(1.0f, -1.0f, -1.0f);
    
    Vector2 textureLeftTop = new Vector2(0.0f, 0.0f);
    Vector2 textureLeftBottom = new Vector2(0.0f, 1.0f);
    Vector2 textureRightTop = new Vector2(1.0f, 0.0f);
    Vector2 textureRightBottom = new Vector2(1.0f, 1.0f);
    
    // Front face.
    cubeVertices[0] = new CustomVertex1(LeftTopFront, textureLeftTop);
    cubeVertices[1] = new CustomVertex1(LeftBottomFront, textureLeftBottom);
    cubeVertices[2] = new CustomVertex1(RightTopFront, textureRightTop);
    cubeVertices[3] = new CustomVertex1(LeftBottomFront, textureLeftBottom);
    cubeVertices[4] = new CustomVertex1(RightBottomFront, textureRightBottom);
    cubeVertices[5] = new CustomVertex1(RightTopFront, textureRightTop);
    

    For a triangle list, you need three vertices for a triangle and two triangles to make the front face of a cube.

  8. Set the data into the vertex buffer data by calling SetData and set the vertex buffer to the device by calling SetVertexBuffer.

    vertexBuffer.SetData<CustomVertex1>(cubeVertices);
    
    graphics.GraphicsDevice.SetVertexBuffer(vertexBuffer);
    
  9. Draw the object by calling DrawPrimitives.

    RasterizerState rasterizerState1 = new RasterizerState();
    rasterizerState1.CullMode = CullMode.None;
    graphics.GraphicsDevice.RasterizerState = rasterizerState1;
    
    foreach (EffectPass pass in basicEffect.CurrentTechnique.Passes)
    {
        pass.Apply();
    
        graphics.GraphicsDevice.DrawPrimitives(
            PrimitiveType.TriangleList,
            0,  // start vertex
            12  // number of primitives to draw
        );
    }
    

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