Create a new project, name it chapter 2.
Project Files: save and import to game..
[save as bullet]
[save as plane]
[save as enemy]
Before we proceed, let's set up the game..
let's say the plane can only fire 1 bullet at a time..
int noOfbullet =1;
Declare the speed,texture,velocity and position variables for the game objects..
Texture2D bullet, plane;
Vector2 bulletPosition, planePosition;
float bulletSpeed = 5f;
//Declare Keyboardstates for input handling
KeyboardState currentKeyboardState,oldKeyboardState;
bool bulletIsAlive = false;
At loadContent
bullet = Content.Load<Texture2D>("bullet");
plane = Content.Load<Texture2D>("plane");
planePosition = new Vector2(GraphicsDevice.Viewport.Width /2 - plane.Width /2, GraphicsDevice.Viewport.Height - 50- plane.Height);
Set the plane position at the lower middle part of the screen.
At the Update Method
set up the input handler
currentKeyboardState = Keyboard.GetState();
if (currentKeyboardState.IsKeyDown(Keys.Right) && oldKeyboardState.IsKeyDown(Keys.Right))
{
planePosition .X += 10;
}
if (currentKeyboardState.IsKeyDown(Keys.Left) && oldKeyboardState.IsKeyDown(Keys.Left))
{
planePosition .X -= 10;
}
oldKeyboardState = currentKeyboardState;
At the Draw Method, draw the plane..
spriteBatch.Begin();
spriteBatch.Draw(plane,planePosition,Color.White);
spriteBatch.End();
RUN THE GAME
Create a method for bulletUpdate..
public void updateBullet()
{
//IF THE BULLET IS ALIVE UPDATE IT AND DRAW IT
if (bulletIsAlive)
{
bulletVelocity = new Vector2(0, bulletSpeed);
bulletPosition.Y -= bulletVelocity.Y;
spriteBatch.Draw(bullet, bulletPosition, Color.White);
//IF THE BULLET IS LESS THAN TO ZERO OR OUT OF BOUNDS KILL THE BULLET SO IT WONT UPDATE
if (bulletPosition.Y < 0)
{
bulletIsAlive = false;
noOfbullet++;
}
}
}
public void fireBullet()
{
// IF THE NUMBER OF BULLET IS EQUAL OR GREATER THAN 1 , FIRE THE BULLET
if (noOfbullet >= 1)
{
bulletIsAlive = true; //MAKE IT ALIVE SO IT WILL UPDATE
noOfbullet--; //SUBTRACT THE 1 from the no of Bullet
bulletPosition = new Vector2(planePosition.X + plane.Width / 2 - bullet.Width / 2,
planePosition.Y); //SET THE POSITION OF THE BULLER ON FIRE
}
}
ADD the updateBullet method in the draw method..
spriteBatch.Begin();
spriteBatch.Draw(plane, planePosition, Color.White);
updateBullet();
spriteBatch.End();
ADD the fireBullet to the update method..
if (currentKeyboardState.IsKeyDown(Keys.Space) && oldKeyboardState.IsKeyDown(Keys.Space))
{
fireBullet(); // IF SPACE IS PRESSED FIRE A BULLET
}
[RUN THE GAME AND FIRE A BULLET]
Now we're going to set up the enemy..
At the bottom of your public Game1 class, create a new class.
class enemy{
public Vector2 position;
public bool alive;
public Texture2D texture;
public enemy()
{
}
}
This will hold the values of enemies..
Then after your game1 class, where you declare variables. Declare a new list of enemies and the enemy number..
List<enemy> enemyList = new List<enemy>();
const int enemyNumber = 5;
At your load content , set up the enemy and add it to the enemy list depending on its number..
for (int x = 0; x <= enemyNumber; x++)
{
int y = 0; //set the y position
enemy n = new enemy(); //create a new enemy
n.texture = Content.Load<Texture2D>("enemy"); // set the current texture of enemy
n.alive = true; //set the enemy alive
n.position = new Vector2(x* 120 , y); //set the position of the enemy
enemyList.Add(n); //add the new enemy to the list of enemies
}
On your Draw Method...
Add the following lines..
foreach (enemy enemy in enemyList) //FOREACH ENEMY IN THE ENEMELIST
{
if (enemy.alive) //IF THE ENEMY IS ALIVE DRAW IT
{
spriteBatch.Draw(enemy.texture, enemy.position, Color.White);
}
}
[NOW RUN THE GAME]
Next create a collision detection...
The method will check 1 enemy..
private void updateEnemies(enemy enemy)
{
if (enemy.alive) //IF THE ENEMY IS ALIVE CHECK THE POSITION OF BULLET AND ENEMY
{
if (bulletPosition.X >= enemy.position.X
&& bulletPosition.X <= enemy.position.X + enemy.texture.Width
&& bulletPosition .Y > enemy .position .Y
&& bulletPosition.Y < enemy.position.Y + enemy.texture.Height)
//CHECK THE BOUNDS OF ENEMY AND BULLET
{
enemy.alive = false; //IF THE BULLET HITS THE ENEMY KILL ENEMY
bulletIsAlive = false; //KILL THE BULLET
noOfbullet++; //ADD 1 BULLET
}
}
}
Now we have the updateEnemies method, we need to place a foreach loop in the Update method that will loop all the enemies in the enemylist and update it by using updateEnemiesforeach (enemy enemy in enemyList)
{
updateEnemies(enemy); //pass the enemy into the updateEnemy Method
}
We're almost done, feel free to edit the source code whatever event you want to take place at the end of the game..
[Challenge : create a method that will update the position or behavior of the enemies..]
SOURCE CODE
using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Audio;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.GamerServices;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
using Microsoft.Xna.Framework.Media;
namespace chapter2
{
public class Game1 : Microsoft.Xna.Framework.Game
{
GraphicsDeviceManager graphics;
SpriteBatch spriteBatch;
Texture2D bullet, plane;
Vector2 bulletPosition, planePosition;
float bulletSpeed = 5f;
int noOfbullet = 1;
KeyboardState currentKeyboardState, oldKeyboardState;
bool bulletIsAlive = false;
Vector2 bulletVelocity = Vector2.Zero;
List enemyList = new List();
const int enemyNumber = 5;
public Game1()
{
graphics = new GraphicsDeviceManager(this);
Content.RootDirectory = "Content";
}
protected override void Initialize()
{
base.Initialize();
}
protected override void LoadContent()
{
spriteBatch = new SpriteBatch(GraphicsDevice);
bullet = Content.Load("bullet");
plane = Content.Load("plane");
planePosition = new Vector2(GraphicsDevice.Viewport.Width / 2 - plane.Width / 2, GraphicsDevice.Viewport.Height - 50 -plane.Height);
for (int x = 0; x <= enemyNumber; x++)
{
int y = 0;
enemy n = new enemy();
n.texture = Content.Load("enemy");
n.alive = true;
n.position = new Vector2(x* 120 , y);
enemyList.Add(n);
}
}
protected override void UnloadContent()
{
}
protected override void Update(GameTime gameTime)
{
currentKeyboardState = Keyboard.GetState();
if (currentKeyboardState.IsKeyDown(Keys.Right) && oldKeyboardState.IsKeyDown(Keys.Right))
{
planePosition.X += 10;
}
if (currentKeyboardState.IsKeyDown(Keys.Left) && oldKeyboardState.IsKeyDown(Keys.Left))
{
planePosition.X -= 10;
}
if (currentKeyboardState.IsKeyDown(Keys.Space) && oldKeyboardState.IsKeyDown(Keys.Space))
{
fireBullet();
}
foreach (enemy enemy in enemyList)
{
updateEnemies(enemy);
}
oldKeyboardState = currentKeyboardState;
base.Update(gameTime);
}
public void updateBullet()
{
if (bulletIsAlive)
{
bulletVelocity = new Vector2(0, bulletSpeed);
bulletPosition.Y -= bulletVelocity.Y;
spriteBatch.Draw(bullet, bulletPosition, Color.White);
if (bulletPosition.Y < 0)
{
bulletIsAlive = false;
noOfbullet++;
}
}
}
public void fireBullet()
{
if (noOfbullet >= 1)
{
bulletIsAlive = true;
noOfbullet--;
bulletPosition = new Vector2(planePosition.X + plane.Width / 2 - bullet.Width / 2,
planePosition.Y);
}
}
private void updateEnemies(enemy enemy)
{
if (enemy.alive)
{
if (bulletPosition.X >= enemy.position.X
&& bulletPosition.X <= enemy.position.X + enemy.texture.Width
&& bulletPosition .Y > enemy .position .Y
&& bulletPosition.Y < enemy.position.Y + enemy.texture.Height)
{
enemy.alive = false;
bulletIsAlive = false;
noOfbullet++;
}
}
}
protected override void Draw(GameTime gameTime)
{
GraphicsDevice.Clear(Color.CornflowerBlue);
spriteBatch.Begin();
spriteBatch.Draw(plane, planePosition, Color.White);
foreach (enemy enemy in enemyList)
{
if (enemy.alive)
{
spriteBatch.Draw(enemy.texture, enemy.position, Color.White);
}
}
updateBullet();
spriteBatch.End();
base.Draw(gameTime);
}
}
class enemy{
public Vector2 position;
public bool alive;
public Texture2D texture;
public enemy()
{
}
}
}
