XNA 4 3D Game Development by Example：Beginner's Guide

上QQ阅读APP看书，第一时间看更新

Time for action – beginning the Camera class

Add a new class to the Cube Chaser project by right-clicking on the project in Solution Explorer and selecting Add | Class....
Ensure that the Visual C# | Code is selected under Installed Templates and select the Class template.
Enter Camera.cs as the name of the class file.
Add the following using directive to the top of the Camera.cs file:
```
using Microsoft.Xna.Framework;
```

Add the following fields and properties to the Camera class:

#region Fields
private Vector3 position = Vector3.Zero;
private float rotation;
#endregion

#region Properties
public Matrix Projection { get; private set; }
#endregion

Add a constructor for the Camera class:

#region Constructor
public Camera(
    Vector3 position, 
    float rotation, 
    float aspectRatio, 
    float nearClip, 
    float farClip)
{
    Projection = Matrix.CreatePerspectiveFieldOfView(
        MathHelper.PiOver4, 
        aspectRatio, 
        nearClip, 
        farClip);
    MoveTo(position, rotation);
}
#endregion

What just happened?

We have now put together some of the basic information our Camera class will track, including the position of the camera and the angle it is facing.

Tip

What is an FPS (First Person Shooter) camera?

When working with cameras in 3D, there are several different kinds of cameras we might want to deal with. An FPS camera, so named because it is the style of camera used in First Person Shooter games, it is a camera that is placed in the location of the character's eyes, resulting in a first-person view. As the player moves, the camera moves and rotates directly with the player. Other types of cameras include chase cameras, which follow along behind the player, and arc-ball cameras, which circle around a fixed point in 3D space. We will implement an arc-ball camera in Chapter 5, Tank Battles – A War-Torn Land.

Additionally, we have defined a matrix, called Projection, which we will create based on the values passed into the constructor for the Camera class. It is defined as a property that can be obtained from outside our code, but can only be set within the Camera class itself.

Tip

What is a matrix?

The short answer is that a matrix is a two-dimensional array of numbers used to transform points in 3D space. The long answer to this question is presented in Chapter 4, Cube Chaser – Finding Your Way, where we will dive into details about what a matrix is and the "magic" behind how they work. For now, we can define a matrix as a construct that we can use to manipulate points by applying different effects to them.

We have not yet defined the MoveTo() method, which will allow us to specify the camera position and rotation in a single call. We need a few more elements in our class before we can implement MoveTo().

Also, note that we have enclosed sections of our code in #region...#endregion directives. These tell the Visual Studio IDE that these sections of the code can be collapsed as a unit to hide the details while we work on other sections of the code. We will use these regions throughout the book to keep our code organized.