Cannot get this triangle to display

Question

I'm following the XNA 3.0 Game Studio Unleashed Book by Chad Carter.

I'm on chapter 4 and the following listing should render a textured triangle onto the game window but for the life of me I cannot figure out why it's not. I just get the plain cornflower blue screen.

I'm using Visual Studio 2008 with XNA 3.1

Those who have the book, I'm up to the top of page 66 where I apply a texture to the triangle.

Any help much appreciated.

namespace XNADemo
{
/// 
/// This is the main type for your game
/// 
public class Game1 : Microsoft.Xna.Framework.Game
{
    GraphicsDeviceManager graphics;
    SpriteBatch spriteBatch;

    private Matrix projection;
    private Matrix view;
    private Matrix world;

    private Vector3 cameraPosition = new Vector3(0.0f, 0.0f, 3.0f);
    private Vector3 cameraTarget = Vector3.Zero;
    private Vector3 cameraUpVector = Vector3.Up;

    private VertexPositionNormalTexture[] vertices;
    private Texture2D texture;
    private BasicEffect effect;

    public Game1()
    {
        graphics = new GraphicsDeviceManager(this);
        Content.RootDirectory = "Content";
    }

    /// 
    /// Allows the game to perform any initialization it needs to before starting to run.
    /// This is where it can query for any required services and load any non-graphic
    /// related content.  Calling base.Initialize will enumerate through any components
    /// and initialize them as well.
    /// 
    protected override void Initialize()
    {
        // TODO: Add your initialization logic here
        InitializeCamera();
        InitializeVertices();            
        base.Initialize();
    }

    /// 
    /// LoadContent will be called once per game and is the place to load
    /// all of your content.
    /// 
    protected override void LoadContent()
    {
        // Create a new SpriteBatch, which can be used to draw textures.
        spriteBatch = new SpriteBatch(GraphicsDevice);

        texture = Content.Load("texture");
        effect = new BasicEffect(graphics.GraphicsDevice, null);



    }

    /// 
    /// UnloadContent will be called once per game and is the place to unload
    /// all content.
    /// 
    protected override void UnloadContent()
    {
        // TODO: Unload any non ContentManager content here
    }

    /// 
    /// Allows the game to run logic such as updating the world,
    /// checking for collisions, gathering input, and playing audio.
    /// 
    /// Provides a snapshot of timing values.
    protected override void Update(GameTime gameTime)
    {
        // Allows the game to exit
        if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
            this.Exit();

        // TODO: Add your update logic here

        base.Update(gameTime);
    }

    /// 
    /// This is called when the game should draw itself.
    /// 
    /// Provides a snapshot of timing values.
    protected override void Draw(GameTime gameTime)
    {
        GraphicsDevice.Clear(Color.CornflowerBlue);
        world = Matrix.Identity;

        graphics.GraphicsDevice.VertexDeclaration = new VertexDeclaration
            (graphics.GraphicsDevice, VertexPositionNormalTexture.VertexElements);


        effect.Projection = projection;
        effect.View = view;

        effect.EnableDefaultLighting();


        effect.World = world;
        effect.TextureEnabled = true;
        effect.Texture = texture;
        effect.Begin();

        foreach (EffectPass pass in effect.CurrentTechnique.Passes)
        {
            pass.Begin();
            graphics.GraphicsDevice.DrawUserPrimitives
                (PrimitiveType.TriangleList, vertices, 0, vertices.Length / 3);
            pass.End();
        }

        effect.End();

        base.Draw(gameTime);
    }


    private void InitializeCamera()
    {
        float aspectRatio = (float)graphics.GraphicsDevice.Viewport.Width /
                            (float)graphics.GraphicsDevice.Viewport.Height;
        Matrix.CreatePerspectiveFieldOfView(MathHelper.PiOver4, aspectRatio, 0.0001f, 1000.0f, out projection);

        Matrix.CreateLookAt(ref cameraPosition, ref cameraTarget, ref cameraUpVector, out view);


    }

    private void InitializeVertices()
    {
        Vector3 position;
        Vector2 textureCoordinates;

        vertices = new VertexPositionNormalTexture[3];

        //top left
        position = new Vector3(-1, 1, 0);
        textureCoordinates = new Vector2(0, 0);
        vertices[0] = new VertexPositionNormalTexture(position, Vector3.Forward, textureCoordinates);

        //bottom right
        position = new Vector3(1, -1, 0);
        textureCoordinates = new Vector2(1, 1);
        vertices[1] = new VertexPositionNormalTexture(position, Vector3.Forward, textureCoordinates);

        //bottom left
        position = new Vector3(-1, -1, 0);
        textureCoordinates = new Vector2(0, 1);
        vertices[1] = new VertexPositionNormalTexture(position, Vector3.Forward, textureCoordinates);  

    }
}

}

user164771 · Accepted Answer

I belive that the index of vertices for the bottom left vertex should be 2 rather than 1

    //bottom right
    position = new Vector3(1, -1, 0);
    textureCoordinates = new Vector2(1, 1);
    vertices[1] = new VertexPositionNormalTexture(position,
    Vector3.Forward, textureCoordinates);

    //bottom left
    position = new Vector3(-1, -1, 0);
    textureCoordinates = new Vector2(0, 1);
    //vertices[1] = new VertexPositionNormalTexture(position,
    vertices[2] = new VertexPositionNormalTexture(position,
    Vector3.Forward, textureCoordinates);

The other possibility which comes to me is the cullmode which is set and the order which vertices are defined. You may be looking at what is deemed the back of the triangle and thus not rendered.

Cannot get this triangle to display

Answers (2)

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