Rotating around created vertices - xna

Question

i recently learn xna and is trying to create a room using vertices. I went and try out Riemeres XNA tutorial and learn alot but i can't seem to make my camera work well, every time i move left or right some of my image or textured seems to disappear and reappear. Please Help.
Here is my code.
public struct MyOwnVertexFormat
{
public Vector3 position;
private Vector2 texCoord;
public MyOwnVertexFormat(Vector3 position, Vector2 texCoord)
{
this.position = position;
this.texCoord = texCoord;
}
public readonly static VertexDeclaration VertexDeclaration = new VertexDeclaration
(
new VertexElement(0, VertexElementFormat.Vector3, VertexElementUsage.Position, 0),
new VertexElement(sizeof(float) * 3, VertexElementFormat.Vector2, VertexElementUsage.TextureCoordinate, 0)
);
}
public class Game1 : Microsoft.Xna.Framework.Game
{
GraphicsDeviceManager graphics;
GraphicsDevice device;
Effect effect;
Matrix viewMatrix;
Matrix projectionMatrix;
VertexBuffer vertexBuffer;
Vector3 cameraPos;
Texture2D streetTexture;
private Vector3 Position = Vector3.One;
private float Zoom = 2500;
private float RotationY = 0.0f;
private float RotationX = 0.0f;
private Matrix gameWorldRotation;
public Game1()
{
graphics = new GraphicsDeviceManager(this);
Content.RootDirectory = "Content";
}
protected override void Initialize()
{
graphics.PreferredBackBufferWidth =1024;
graphics.PreferredBackBufferHeight = 768;
graphics.IsFullScreen = false;
graphics.ApplyChanges();
base.Initialize();
}
protected override void LoadContent()
{
device = GraphicsDevice;
effect = Content.Load<Effect>("OurHLSLfile"); SetUpVertices();
SetUpCamera();
streetTexture = Content.Load<Texture2D>("streettexture");
}
private void UpdateKeyboard()
{
if (Keyboard.GetState().IsKeyDown(Keys.Escape))
Exit();
if (Keyboard.GetState().IsKeyDown(Keys.Up))
RotationX += 1.0f;
if (Keyboard.GetState().IsKeyDown(Keys.Down))
RotationX -= 1.0f;
if (Keyboard.GetState().IsKeyDown(Keys.Left))
RotationY += 1.0f;
if (Keyboard.GetState().IsKeyDown(Keys.Right))
RotationY -= 1.0f;
gameWorldRotation =
Matrix.CreateRotationX(MathHelper.ToRadians(RotationX)) *
Matrix.CreateRotationY(MathHelper.ToRadians(RotationY));
}
private void SetUpVertices()
{
MyOwnVertexFormat[] vertices = new MyOwnVertexFormat[12];
vertices[0] = new MyOwnVertexFormat(new Vector3(-20, 0, 10), new Vector2(-0.25f, 25.0f));
vertices[1] = new MyOwnVertexFormat(new Vector3(-20, 0, -100), new Vector2(-0.25f, 0.0f));
vertices[2] = new MyOwnVertexFormat(new Vector3(2, 0, 10), new Vector2(0.25f, 25.0f));
vertices[3] = new MyOwnVertexFormat(new Vector3(2, 0, -100), new Vector2(0.25f, 0.0f));
vertices[4] = new MyOwnVertexFormat(new Vector3(2, 1, 10), new Vector2(0.375f, 25.0f));
vertices[5] = new MyOwnVertexFormat(new Vector3(2, 1, -100), new Vector2(0.375f, 0.0f));
vertices[6] = new MyOwnVertexFormat(new Vector3(3, 1, 10), new Vector2(0.5f, 25.0f));
vertices[7] = new MyOwnVertexFormat(new Vector3(3, 1, -100), new Vector2(0.5f, 0.0f));
vertices[8] = new MyOwnVertexFormat(new Vector3(-13, 1, 10), new Vector2(0.75f, 25.0f));
vertices[9] = new MyOwnVertexFormat(new Vector3(-13, 1, -100), new Vector2(0.75f, 0.0f));
vertices[10] = new MyOwnVertexFormat(new Vector3(-13, 21, 10), new Vector2(1.25f, 25.0f));
vertices[11] = new MyOwnVertexFormat(new Vector3(-13, 21, -100), new Vector2(1.25f, 0.0f));
vertexBuffer = new VertexBuffer(device, MyOwnVertexFormat.VertexDeclaration, vertices.Length, BufferUsage.WriteOnly);
vertexBuffer.SetData(vertices);
}
private void SetUpCamera()
{
cameraPos = new Vector3(-25, 13, 75);
viewMatrix = Matrix.CreateLookAt(cameraPos, new Vector3(0, 2, -12), new Vector3(0, 1, 0));
projectionMatrix = Matrix.CreatePerspectiveFieldOfView(MathHelper.PiOver4, device.Viewport.AspectRatio, 1.0f, 5000.0f);
}
protected override void UnloadContent()
{
}
protected override void Update(GameTime gameTime)
{
if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
this.Exit();
UpdateKeyboard();
base.Update(gameTime);
}
protected override void Draw(GameTime gameTime)
{
device.Clear(ClearOptions.Target | ClearOptions.DepthBuffer, Color.DarkSlateBlue, 1.0f, 0);
effect.CurrentTechnique = effect.Techniques["Simplest"];
effect.Parameters["xViewProjection"].SetValue(viewMatrix * projectionMatrix * gameWorldRotation);
effect.Parameters["xTexture"].SetValue(streetTexture);
foreach (EffectPass pass in effect.CurrentTechnique.Passes)
{
pass.Apply();
device.SetVertexBuffer(vertexBuffer);
device.DrawPrimitives(PrimitiveType.TriangleStrip, 0, 10);
}
base.Draw(gameTime);
}
}

Answer 1

I assume it's a projection issue. This line, taken from your code, strengthens my assumption:
viewMatrix * projectionMatrix * gameWorldRotation
tl;dr, the correct order is:
gameWorldRotation * viewMatrix * projectionMatrix
Please remember that order matters when multiplying matrices. In mathematical terms:
Matrix multiplication is not commutative!
Those three matrices map a vector to three different coordinate systems, the world, view and projection space. Usually vertices are defined in object space. Multiplying a vector with the world (view, projection) matrix brings your vector to world (view, projection) space:
object space => world space => view space => projection space
XNA uses a row vector layout (as opposed to column vectors). That means a vector is declared horizontally (x, y, z). Skipping the dry interesting details, it means that when transforming a vector (multiplying the vector with a matrix), the vector is the left operand, while the matrix is the right operand:
A := [3x3 Matrix]
(x, y, z) * A = (x', y', z') // The result is another 3D vector
Now in order to apply all three matrices we simply use the result of the previous transformation as input for the next transform:
W .... world matrix
V .... view matrix
W .... projection matrix
x .... vector
x' ... transformed vector
x' = ((x * W) * V) * P
Finally, matrix multiplication is associative (braces don't matter). And that's why we can combine the world, view and projection matrix into a single matrix before sending it to the device:
x' = ((x * W) * V) * P = x * W * V * P = x * (W * V * P)
World * View * Projection. That's all you need. (And maybe some basic matrix math for your future work.)