Player Behavior

Introduction

At this point we have a ship which is visible on Screen, but it doesn't do anything. This tutorial will add behavior to our Player Entity so that it can move, turn, and shoot.

Adding Variables

For this game, the Player will continuously move forward at a constant speed. The Player object will be turned left and right with the keyboard or Xbox gamepad. Before we begin writing any code we'll add two variables to Player: MovementSpeed and TurningSpeed. To do this:

  1. Select the Player entity in Glue

  2. Select the Variables tab

  3. Click the Add New Variable button

  4. Leave the defaults Create a new variable option and float type

  5. Enter the name MovementSpeed

  6. Click OK

Repeat the steps above to also add a TurningSpeed variable.

Next let's give the variables some default values:

  1. Enter a value of 100 for MovementSpeed. This is the number of pixels the Player will travel in one second.

  2. Enter a value of 3.14 for TurningSpeed. This is the maximum number of radians the Player will rotate in one second.

Applying Movement

To apply movement we will need to write some C# code. To do this:

  1. Open the project in Visual Studio (or switch to Visual Studio if you already have it open)

  2. Open Player.cs. This will be in the Entities folder in the Solution Explorer.

  3. Scroll to the CustomActivity method in Player.cs

Modify CustomActivity as shown in the following snippet:

void CustomActivity()
{
   this.Velocity = this.RotationMatrix.Up * this.MovementSpeed;
}

If you now run the game you will see the ship move upward, then eventually move off-screen.

What is "RotationMatrix.Up"?: If you are unfamiliar with the RotationMatrix property, or with matrices in general then you may be wondering about the RotationMatrix.Up variable, and why we're using it. The RotationMatrix property contains information about how an Entity, Sprite, or any other PositionedObject is rotated. The Up property indicates you which way is "up" for the object given its current rotation. This value is in "object space" meaning that if the object rotates, then this value will rotate along with the object. This is especially convenient for this tutorial because this game will have the ships always moving forward. The code above will work regardless of which way the Player is rotated - something which we'll see in the coming sections.

Assigning Input

The next step is to assign input logic so the Player can turn. We will add an object to our Player representing the input device. This could be a gampad, keyboard, or any other object. By using the I1DInput interface, we can write the code the same regardless of the actual hardware used to control the Player. Modify Player.cs as shown in the following snippet:

public I1DInput TurningInput { get; set; }

private void CustomInitialize()
{
 // we'll default to using the gamepad if one is
 // plugged in. Otherwise, we'll use the keyboard
 if(InputManager.Xbox360GamePads[0].IsConnected)
 {
  TurningInput = 
    InputManager.Xbox360GamePads[0].LeftStick.Horizontal;
 }
 else
 {
  TurningInput = InputManager.Keyboard.Get1DInput(
    Microsoft.Xna.Framework.Input.Keys.Left, 
    Microsoft.Xna.Framework.Input.Keys.Right);
 }
}

private void CustomActivity()
{
 this.RotationZVelocity =
 // Negative value is needed so that holding "left" turns to the left
   -TurningInput.Value * this.TurningSpeed;
   this.Velocity = this.RotationMatrix.Up * this.MovementSpeed;
}

Note that all of the code we have written uses coefficients (MovementSpeed and TurningSpeed) defined in Glue. This means that you can modify these values in the Player Entity at any time if you want to tune how the game feels. For example, if you want the ship to turn faster, increase TurningSpeed to a larger value.

Adding Bullet Sprite

Next we will give the Bullet a PNG file and a Sprite to use. This process is essentially the same as when we added PNG files and a Sprite to our Player Entity so you may find these steps familiar. To add the PNG:

  1. Expand the Bullet entity in Glue

  2. Drag+drop Bullet1.png onto the Files folder in the Bullet

To add a Sprite to the Bullet entity:

  1. Select the Bullet entity in Glue

  2. Click the Quick Actions tab

  3. Click the Add Object to Bullet button

  4. Select the Sprite type

  5. Click OK

Now we can set the Sprite's Texture:

  1. Expand the Bullet Entity's Object folder

  2. Select the newly-created SpriteInstance

  3. Select the Variables tab

  4. Set the Texture drop-down to Bullet1

Shooting

The next step is to add firing bullets. We'll be using the BulletFactory which we created in an earlier tutorial to create a new bullet and automatically add it to the GameScreen's BulletList. For more information on factories, see the tutorial on this topic. Next we will need to define a bullet speed. To do this:

  1. Click the Bullet entity in Glue

  2. Click the Variables tab

  3. Click the Add New Variable button

  4. Leave the defaults

  5. Set the variable name to MovementSpeed

  6. Set MovementSpeed to 300

Now we can use BulletFactory to create bullets when the player shoots. To do this:

  1. Go to Player.cs in Visual Studio

  2. Modify the Player.cs code so that it contains the following code:

public I1DInput TurningInput { get; set; }
public IPressableInput ShootingInput { get; set; }

private void CustomInitialize()
{
 // we'll default to using the gamepad if one is
 // plugged in. Otherwise, we'll use the keyboard
 if(InputManager.Xbox360GamePads[0].IsConnected)
 {
  TurningInput = 
   InputManager.Xbox360GamePads[0].LeftStick.Horizontal;
  ShootingInput = InputManager.Xbox360GamePads[0].GetButton(
   Xbox360GamePad.Button.A);
 }
 else
 {
  TurningInput = InputManager.Keyboard.Get1DInput(
   Microsoft.Xna.Framework.Input.Keys.Left, 
   Microsoft.Xna.Framework.Input.Keys.Right);
  ShootingInput = InputManager.Keyboard.GetKey(
   Microsoft.Xna.Framework.Input.Keys.Space);
 }
}

private void CustomActivity()
{
 this.RotationZVelocity =
  // Negative value is needed so that holding "left" turns to the left
  -TurningInput.Value * this.TurningSpeed;
 this.Velocity = this.RotationMatrix.Up * this.MovementSpeed;

 if (ShootingInput.WasJustPressed)
 {
  // We'll create 2 bullets because it looks much cooler than 1
  Bullet firstBullet = Factories.BulletFactory.CreateNew();
  firstBullet.Position = this.Position;
  firstBullet.Position += this.RotationMatrix.Up * 12;
  // This is the bullet on the right side when the ship is facing up.
  // Adding along the Right vector will move it to the right relative to the ship
  firstBullet.Position += this.RotationMatrix.Right * 6;
  firstBullet.RotationZ =