Step 6: Consequences

Now we'll make the bullets lethal.

• First let's create a title screen that we can start on and return to after death.
  • Create a TitleStage.cs file:

using System.Collections;
using System.Collections.Generic;

using GameAPI;
using GameAPI.BudgetBoy;

namespace Games.TestGame
{
    public class TitleStage : Stage
    {
        public new Main Game { get { return (Main) base.Game; } }

        // called when this stage is created
        public TitleStage(Main game) : base(game)
        {

        }

        // called when this stage is entered
        protected override void OnEnter()
        {
            Graphics.SetClearColor(Game.Swatches.ClearColor); // set the background color

            // get the bitmap font resource
            Image font = Graphics.GetImage("Resources", "font");
            int TEXT_DEPTH = 0;

            // create and add text to the stage for the game's title
            Text titleText = Add(new Text(font, Game.Swatches.White), TEXT_DEPTH);
            titleText.Value = "TEST GAME";
            titleText.Position = Graphics.Size / 2 + new Vector2i(-titleText.Width / 2, 30);

            // create and add text to the stage for the game's instructions
            Text instructionText = Add(new Text(font, Game.Swatches.White), TEXT_DEPTH);
            instructionText.Value = "press A to start";
            instructionText.Position = Graphics.Size / 2 + new Vector2i(-instructionText.Width / 2, -30);
        }

        // called each tick
        protected override void OnUpdate()
        {
            base.OnUpdate();

            // start the game when the A button is pressed (not actually the "A" key on the keyboard, defaults to Z)
            if(Controls.A.JustPressed)
                Game.SetStage(new GameStage(Game));
        }

        // called when this stage is rendered
        protected override void OnRender()
        {
            base.OnRender();

        }
    }
}

• To use the Text class, we'll need a 16x16 (character, not pixel) bitmap font image. In this case it's the font.png file in the Resources folder.

In TitleStage's OnEnter method, we're creating some Text objects and adding them to the stage.

In TitleStage's OnUpdate method, we're checking to see if the A button (by default the Z key) has been pressed this frame. If so, we're creating a new instance of GameStage and switching to that stage.

• In GameStage.cs, we'll create a new member variable (a List that can hold Bullets):

List<Bullet> _bullets = new List<Bullet>();

• When we create a new bullet, we need to keep track of it by adding it to this list.
• When we want to destroy a bullet, we have to remember to remove it from this list.

void AddBullet(Vector2f pos, bool movingDownward)
{
    Bullet bullet = Add(new Bullet(movingDownward), 1);
    bullet.Position = pos;

    // save the bullet to our list so we can keep track of it
    _bullets.Add(bullet);
}

public void RemoveBullet(Bullet bullet)
{
    // remove the bullet from our list (we no longer want to keep track of it)
    _bullets.Remove(bullet);

    // remove the bullet from the stage (this destroys it)
    Remove(bullet);
}

• The bullet class now needs to call ((GameStage)Stage).RemoveBullet(this) instead of just Stage.Remove(this).

  ---

• Let's also keep track of the player by adding a _player member variable to GameStage.cs.
• Now that we have a reference to everything we need to access, we can check collision between the player and the bullets.
  • In GameStage's OnUpdate method, check the distance (or distance squared, because it's faster) from each bullet to the player. If the distance is too low, then they're touching, and the player's dead.

protected override void OnUpdate()
{
    base.OnUpdate();

    // check collision between player and bullets
    foreach(Bullet bullet in _bullets)
    {
        // check distance from each bullet to the player
        float distSqr = (bullet.Position - _player.Position).LengthSquared;
        if(distSqr < 150.0f)
        {
            // player's dead, restart game
            Game.SetStage(new TitleStage(Game));
        }
    }
}

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