# How to: Make a First-Person Camera

XNA Game Studio Express
This example demonstrates how to create a first-person camera.

The example controls the camera by using the method shown in How to: Rotate and Move a Camera, with an additional offset for the camera to place it where the game avatar's head should be. The example assumes a model has been added to the project as described in How to: Render a Model.

### To make a first-person camera

1. Precalculate the camera's offset from the avatar. The offset is used to place the camera roughly where the avatar's head is.

```Vector3 avatarHeadOffset = new Vector3( 0, 10, 0 );
```
2. Track the position and rotation of the avatar during gameplay.
3. Create a rotation Matrix using CreateRotationY and the avatar's current direction.

```Matrix rotationMatrix = Matrix.CreateRotationY( avatarYaw );
```
4. Transform a copy of the camera's head offset using the rotation Matrix and Vector3.Transform.

```// Transform the head offset so the camera is positioned properly relative to the avatar.
Vector3 headOffset = Vector3.Transform( avatarHeadOffset, rotationMatrix );
```
5. Calculate the current position of the camera. The position of the camera will be the position of the avatar plus the avatar's transformed head offset.

```// Calculate the camera's current position.
Vector3 cameraPosition = avatarPosition + headOffset;
```
6. Transform a copy of the camera's reference vector using the rotation Matrix and Vector3.Transform.

```// Create a vector pointing the direction the camera is facing.
Vector3 transformedReference = Vector3.Transform( cameraReference, rotationMatrix );
```
7. Calculate the position the camera is looking at. This "look-at" position will be the camera's position plus the camera's transformed reference vector.

```// Calculate the position the camera is looking at.
Vector3 cameraLookat = transformedReference + cameraPosition;
```
8. Create a new view Matrix. The new Matrix is created by passing the camera position and camera lookat to CreateLookAt. The view Matrix controls how world coordinate values are transformed to camera coordinates.

```view = Matrix.CreateLookAt( cameraPosition, cameraLookat, new Vector3( 0.0f, 1.0f, 0.0f ) );
```
9. Create a new projection Matrix with CreatePerspectiveFieldOfView. The projection Matrix controls how camera coordinate values are transformed to screen coordinates.

```Viewport viewport = graphics.GraphicsDevice.Viewport;
float aspectRatio = (float)viewport.Width / (float)viewport.Height;

proj = Matrix.CreatePerspectiveFieldOfView( viewAngle, aspectRatio, nearClip, farClip );
```
10. Loop through each model in the world drawing it as described in How to: Render a Model using the projection matrix and view matrix created above. For the world matrix, use Matrix.CreateTranslation and the object's current position in the world.

```void DrawBoxes()
{
for (int z = 0; z < 9; z++)
{
for (int x = 0; x < 9; x++)
{
DrawModel( box, Matrix.CreateTranslation( x * 60, 0, z * 60 ), boxTexture );
}
}
}

void DrawModel( Model model, Matrix world, Texture2D texture )
{
foreach (ModelMesh mesh in model.Meshes)
{
foreach (BasicEffect be in mesh.Effects)
{
be.Projection = proj;
be.View = view;
be.World = world;
be.Texture = texture;
be.TextureEnabled = true;
}
mesh.Draw();
}
}
```
```//Game1.cs
using System;
using System.Collections.Generic;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Audio;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
using Microsoft.Xna.Framework.Storage;
using Microsoft.Xna.Framework.Content;

class Game1 : Microsoft.Xna.Framework.Game
{
ContentManager content;
GraphicsDeviceManager graphics;

Matrix view;
Matrix proj;

Model box;
Texture2D boxTexture;
Texture2D avatarTexture;

// Set the avatar position and rotation variables.
Vector3 avatarPosition = new Vector3( 0, 0, -20 );

Vector3 avatarHeadOffset = new Vector3( 0, 10, 0 );

float avatarYaw;

// Set the direction the camera points without rotation.
Vector3 cameraReference = new Vector3( 0, 0, 10 );

Vector3 thirdPersonReference = new Vector3( 0, 500, -500 );

// Set rates in world units per 1/60th second (the default fixed-step interval).
float rotationSpeed = 1f / 60f;
//float forwardSpeed = 500f / 60f;
float forwardSpeed = 50f / 60f;

// Set field of view of the camera in radians (pi/4 is 45 degrees).
static float viewAngle = MathHelper.PiOver4;

// Set distance from the camera of the near and far clipping planes.
//static float nearClip = 5.0f;
static float nearClip = 1.0f;
static float farClip = 2000.0f;

// Set the camera state, avatar's center, first-person, third-person.
int cameraState;
bool cameraStateKeyDown;

public Game1()
{
graphics = new GraphicsDeviceManager( this );
content = new ContentManager( Services );
}

protected override void Initialize()
{
// TODO: Add your initialization logic here.

base.Initialize();
}

protected override void LoadGraphicsContent( bool loadAllContent )
{
{
box = content.Load<Model>( "box" );
boxTexture = content.Load<Texture2D>( "boxtexture" );
avatarTexture = content.Load<Texture2D>( "avatartexture" );
}
}

protected override void UnloadGraphicsContent( bool unloadAllContent )
{
{
}
}

protected override void Update( GameTime gameTime )
{
// Allows the default game to exit on Xbox 360 and Windows.
if (GamePad.GetState( PlayerIndex.One ).Buttons.Back == ButtonState.Pressed)
this.Exit();

GetCurrentCamera();
UpdateAvatarPosition();

base.Update( gameTime );
}

protected override void Draw( GameTime gameTime )
{
graphics.GraphicsDevice.Clear( Color.CornflowerBlue );

switch (cameraState)
{
default:
case 0:
UpdateCamera();
break;
case 1:
UpdateCameraFirstPerson();
break;
case 2:
UpdateCameraThirdPerson();
break;
}
//graphics.GraphicsDevice.RenderState.CullMode = CullMode.None;
DrawBoxes();
Matrix World = Matrix.CreateRotationY( avatarYaw ) * Matrix.CreateTranslation( avatarPosition );
if (cameraState == 2)
{
DrawModel( box, World, avatarTexture );
}

base.Draw( gameTime );
}

// Update the position and direction of the avatar.
void UpdateAvatarPosition()
{
KeyboardState keyboardState = Keyboard.GetState();

if (keyboardState.IsKeyDown( Keys.Left ) || (currentState.DPad.Left == ButtonState.Pressed))
{
// Rotate left.
avatarYaw += rotationSpeed;
}
if (keyboardState.IsKeyDown( Keys.Right ) || (currentState.DPad.Right == ButtonState.Pressed))
{
// Rotate right.
avatarYaw -= rotationSpeed;
}
if (keyboardState.IsKeyDown( Keys.Up ) || (currentState.DPad.Up == ButtonState.Pressed))
{
Matrix forwardMovement = Matrix.CreateRotationY( avatarYaw );
Vector3 v = new Vector3( 0, 0, forwardSpeed );
v = Vector3.Transform( v, forwardMovement );
avatarPosition.Z += v.Z;
avatarPosition.X += v.X;
}
if (keyboardState.IsKeyDown( Keys.Down ) || (currentState.DPad.Down == ButtonState.Pressed))
{
Matrix forwardMovement = Matrix.CreateRotationY( avatarYaw );
Vector3 v = new Vector3( 0, 0, -forwardSpeed );
v = Vector3.Transform( v, forwardMovement );
avatarPosition.Z += v.Z;
avatarPosition.X += v.X;
}
}
void GetCurrentCamera()
{
KeyboardState keyboardState = Keyboard.GetState();

// Toggle the state of the camera.
if (keyboardState.IsKeyDown( Keys.Tab ) || (currentState.Buttons.LeftShoulder == ButtonState.Pressed))
{
cameraStateKeyDown = true;
}
else if (cameraStateKeyDown == true)
{
cameraStateKeyDown = false;
cameraState += 1;
cameraState %= 3;
}
}

void UpdateCamera()
{
// Calculate the camera's current position.
Vector3 cameraPosition = avatarPosition;

Matrix rotationMatrix = Matrix.CreateRotationY( avatarYaw );

// Create a vector pointing the direction the camera is facing.
Vector3 transformedReference = Vector3.Transform( cameraReference, rotationMatrix );

// Calculate the position the camera is looking at.
Vector3 cameraLookat = cameraPosition + transformedReference;

// Set up the view matrix and projection matrix.
view = Matrix.CreateLookAt( cameraPosition, cameraLookat, new Vector3( 0.0f, 1.0f, 0.0f ) );

Viewport viewport = graphics.GraphicsDevice.Viewport;
float aspectRatio = (float)viewport.Width / (float)viewport.Height;

proj = Matrix.CreatePerspectiveFieldOfView( viewAngle, aspectRatio, nearClip, farClip );
}

void UpdateCameraFirstPerson()
{
Matrix rotationMatrix = Matrix.CreateRotationY( avatarYaw );

// Transform the head offset so the camera is positioned properly relative to the avatar.
Vector3 headOffset = Vector3.Transform( avatarHeadOffset, rotationMatrix );

// Calculate the camera's current position.
Vector3 cameraPosition = avatarPosition + headOffset;

// Create a vector pointing the direction the camera is facing.
Vector3 transformedReference = Vector3.Transform( cameraReference, rotationMatrix );

// Calculate the position the camera is looking at.
Vector3 cameraLookat = transformedReference + cameraPosition;

// Set up the view matrix and projection matrix.

view = Matrix.CreateLookAt( cameraPosition, cameraLookat, new Vector3( 0.0f, 1.0f, 0.0f ) );

Viewport viewport = graphics.GraphicsDevice.Viewport;
float aspectRatio = (float)viewport.Width / (float)viewport.Height;

proj = Matrix.CreatePerspectiveFieldOfView( viewAngle, aspectRatio, nearClip, farClip );

}

void UpdateCameraThirdPerson()
{
Matrix rotationMatrix = Matrix.CreateRotationY( avatarYaw );

// Create a vector pointing the direction the camera is facing.
Vector3 transformedReference = Vector3.Transform( thirdPersonReference, rotationMatrix );

// Calculate the position the camera is looking from.
Vector3 cameraPosition = transformedReference + avatarPosition;

// Set up the view matrix and projection matrix.
view = Matrix.CreateLookAt( cameraPosition, avatarPosition, new Vector3( 0.0f, 1.0f, 0.0f ) );

Viewport viewport = graphics.GraphicsDevice.Viewport;
float aspectRatio = (float)viewport.Width / (float)viewport.Height;

proj = Matrix.CreatePerspectiveFieldOfView( viewAngle, aspectRatio, nearClip, farClip );

}

void DrawBoxes()
{
for (int z = 0; z < 9; z++)
{
for (int x = 0; x < 9; x++)
{
DrawModel( box, Matrix.CreateTranslation( x * 60, 0, z * 60 ), boxTexture );
}
}
}

void DrawModel( Model model, Matrix world, Texture2D texture )
{
foreach (ModelMesh mesh in model.Meshes)
{
foreach (BasicEffect be in mesh.Effects)
{
be.Projection = proj;
be.View = view;
be.World = world;
be.Texture = texture;
be.TextureEnabled = true;
}
mesh.Draw();
}
}

}
```