Riemers2DXNA10smoketrail
This chapter will be pretty straightforward if you’ve been following allow the way, so it makes a nice exercise to practice a bit. The idea is simple enough: for each position of the rocket, we will add a small smoke image.
Start by importing the smoke.png image into your content project and then add a new variable into the Properties section of our code to store the Texture data:
private Texture2D _smokeTexture;And initialize it in our LoadContent method:
_smokeTexture = Content.Load<Texture2D>("smoke");There is one thing that makes the next task a bit difficult, we don’t know exactly how many smoke particles we will need, so we don’t know how many positions we need to store. But that is easily solved by using a default .NET feature, the List. A list is a collection that you do not need to specify its size, just add or remove items to/from it when you want.
The List is provided by a different part of the .NET Framework, so we need to add a new using to the top of the file, so add the following:
using System.Collections.Generic;Next, add the following to the Properties section our code:
private List<Vector2> _smokeList = new List<Vector2> ();
private Random _randomizer = new Random();We declare the List that will be used to store Vector2 objects and we initialize it as an empty List so it is ready to use. The second variable we are adding is very useful in game programming, it will generate random numbers whenever we ask it to. We will use some random numbers in this chapter as we will add a small amount of random deviation to the position of the smoke particles.
Next, we can update our UpdateRocket method to store the smoke position in our List, add this code to the end of the if-block in the UpdateRocket method:
Vector2 smokePos = _rocketPosition;
smokePos.X += _randomizer.Next(10) - 5;
smokePos.Y += _randomizer.Next(10) - 5;
_smokeList.Add(smokePos);This retrieves the current position of the rocket and adds a random component to both the X and Y coordinates. The randomizer is asked for a random number between 0 and 10, from which we subtract 5 resulting in a random number between -5 and 5. The resulting position is stored in our smokeList!
All we need to do now is draw the smoke image at each position stored in the smokeList. To this end, we will code a new DrawSmoke method:
private void DrawSmoke()
{
for (int i = 0; i < _smokeList.Count; i++)
{
_spriteBatch.Draw(_smokeTexture, _smokeList[i], null, Color.White, 0, new Vector2(40, 35), 0.2f, SpriteEffects.None, 1);
}
}For each position stored in the smokeList we draw a smokeTexture. Since we’re not adjusting any of the stuff inside the List, as this is in an Update loop, we still use a for-loop for performance.
Don’t forget to call this method from inside our Draw method:
DrawSmoke();Now try to run this code! When you fire a rocket, you should see a fine trail of smoke behind our rocket. We want some more smoke, so instead of adding just one particle at a time we will add 5 in our UpdateRocket method:
for (int i = 0; i < 5; i++)
{
Vector2 smokePos = _rocketPosition;
smokePos.X += _randomizer.Next(10) - 5;
smokePos.Y += _randomizer.Next(10) - 5;
_smokeList.Add(smokePos);
}That’s it for this chapter!
You can try these exercises to practice what you have learned:
- Try changing the frequency and number of smoke particles
- See if you can clear the smoke particle list once the rocket leaves the screen
using System;
using System.Collections.Generic;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
namespace Series2D1
{
public struct PlayerData
{
public Vector2 Position;
public bool IsAlive;
public Color Color;
public float Angle;
public float Power;
}
public class Game1 : Game
{
//Properties
private GraphicsDeviceManager _graphics;
private SpriteBatch _spriteBatch;
private GraphicsDevice _device;
private Texture2D _backgroundTexture;
private Texture2D _foregroundTexture;
private Texture2D _carriageTexture;
private Texture2D _cannonTexture;
private Texture2D _rocketTexture;
private Texture2D _smokeTexture;
private SpriteFont _font;
private int _screenWidth;
private int _screenHeight;
private PlayerData[] _players;
private int _numberOfPlayers = 4;
private float _playerScaling;
private int _currentPlayer = 0;
private bool _rocketFlying = false;
private Vector2 _rocketPosition;
private Vector2 _rocketDirection;
private float _rocketAngle;
private float _rocketScaling = 0.1f;
private Color[] _playerColors = new Color[10]
{
Color.Red,
Color.Green,
Color.Blue,
Color.Purple,
Color.Orange,
Color.Indigo,
Color.Yellow,
Color.SaddleBrown,
Color.Tomato,
Color.Turquoise
};
private List<Vector2> _smokeList = new List<Vector2>();
private Random _randomizer = new Random();
public Game1()
{
_graphics = new GraphicsDeviceManager(this);
Content.RootDirectory = "Content";
}
protected override void Initialize()
{
// TODO: Add your initialization logic here
_graphics.PreferredBackBufferWidth = 500;
_graphics.PreferredBackBufferHeight = 500;
_graphics.IsFullScreen = false;
_graphics.ApplyChanges();
Window.Title = "Riemer's 2D MonoGame Tutorial";
base.Initialize();
}
private void SetUpPlayers()
{
_players = new PlayerData[_numberOfPlayers];
for (int i = 0; i < _numberOfPlayers; i++)
{
_players[i].IsAlive = true;
_players[i].Color = _playerColors[i];
_players[i].Angle = MathHelper.ToRadians(90);
_players[i].Power = 100;
}
_players[0].Position = new Vector2(100, 193);
_players[1].Position = new Vector2(200, 212);
_players[2].Position = new Vector2(300, 361);
_players[3].Position = new Vector2(400, 164);
}
protected override void LoadContent()
{
_spriteBatch = new SpriteBatch(GraphicsDevice);
_device = _graphics.GraphicsDevice;
// TODO: use this.Content to load your game content here
_backgroundTexture = Content.Load<Texture2D>("background");
_foregroundTexture = Content.Load<Texture2D>("foreground");
_carriageTexture = Content.Load<Texture2D>("carriage");
_cannonTexture = Content.Load<Texture2D>("cannon");
_rocketTexture = Content.Load<Texture2D>("rocket");
_smokeTexture = Content.Load<Texture2D>("smoke");
_font = Content.Load<SpriteFont>("myFont");
_screenWidth = _device.PresentationParameters.BackBufferWidth;
_screenHeight = _device.PresentationParameters.BackBufferHeight;
SetUpPlayers();
_playerScaling = 40.0f / (float)_carriageTexture.Width;
}
private void ProcessKeyboard()
{
KeyboardState keybState = Keyboard.GetState();
if (keybState.IsKeyDown(Keys.Left))
{
_players[_currentPlayer].Angle -= 0.01f;
}
if (keybState.IsKeyDown(Keys.Right))
{
_players[_currentPlayer].Angle += 0.01f;
}
if (_players[_currentPlayer].Angle > MathHelper.PiOver2)
{
_players[_currentPlayer].Angle = -MathHelper.PiOver2;
}
if (_players[_currentPlayer].Angle < -MathHelper.PiOver2)
{
_players[_currentPlayer].Angle = MathHelper.PiOver2;
}
if (keybState.IsKeyDown(Keys.Down))
{
_players[_currentPlayer].Power -= 1;
}
if (keybState.IsKeyDown(Keys.Up))
{
_players[_currentPlayer].Power += 1;
}
if (keybState.IsKeyDown(Keys.PageDown))
{
_players[_currentPlayer].Power -= 20;
}
if (keybState.IsKeyDown(Keys.PageUp))
{
_players[_currentPlayer].Power += 20;
}
if (_players[_currentPlayer].Power > 1000)
{
_players[_currentPlayer].Power = 1000;
}
if (_players[_currentPlayer].Power < 0)
{
_players[_currentPlayer].Power = 0;
}
if (keybState.IsKeyDown(Keys.Enter) || keybState.IsKeyDown(Keys.Space))
{
_rocketFlying = true;
_rocketPosition = _players[_currentPlayer].Position;
_rocketPosition.X += 20;
_rocketPosition.Y -= 10;
_rocketAngle = _players[_currentPlayer].Angle;
Vector2 up = new Vector2(0, -1);
Matrix rotMatrix = Matrix.CreateRotationZ(_rocketAngle);
_rocketDirection = Vector2.Transform(up, rotMatrix);
_rocketDirection *= _players[_currentPlayer].Power / 50.0f;
}
}
private void UpdateRocket()
{
if (_rocketFlying)
{
Vector2 gravity = new Vector2(0, 1);
_rocketDirection += gravity / 10.0f;
_rocketPosition += _rocketDirection;
_rocketAngle = (float)Math.Atan2(_rocketDirection.X, -_rocketDirection.Y);
for (int i = 0; i < 5; i++)
{
Vector2 smokePos = _rocketPosition;
smokePos.X += _randomizer.Next(10) - 5;
smokePos.Y += _randomizer.Next(10) - 5;
_smokeList.Add(smokePos);
}
}
}
protected override void Update(GameTime gameTime)
{
if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed ||
Keyboard.GetState().IsKeyDown(Keys.Escape))
{
Exit();
}
// TODO: Add your update logic here
ProcessKeyboard();
UpdateRocket();
base.Update(gameTime);
}
protected override void Draw(GameTime gameTime)
{
GraphicsDevice.Clear(Color.CornflowerBlue);
// TODO: Add your drawing code here
_spriteBatch.Begin();
DrawScenery();
DrawPlayers();
DrawText();
DrawRocket();
DrawSmoke();
_spriteBatch.End();
base.Draw(gameTime);
}
private void DrawScenery()
{
Rectangle screenRectangle = new Rectangle(0, 0, _screenWidth, _screenHeight);
_spriteBatch.Draw(_backgroundTexture, screenRectangle, Color.White);
_spriteBatch.Draw(_foregroundTexture, screenRectangle, Color.White);
}
private void DrawPlayers()
{
for (int i = 0; i < _players.Length; i++)
{
if (_players[i].IsAlive)
{
int xPos = (int)_players[i].Position.X;
int yPos = (int)_players[i].Position.Y;
Vector2 cannonOrigin = new Vector2(11, 50);
_spriteBatch.Draw(_carriageTexture, _players[i].Position, null, _players[i].Color, 0, new Vector2(0, _carriageTexture.Height), _playerScaling, SpriteEffects.None, 0);
_spriteBatch.Draw(_cannonTexture, new Vector2(xPos + 20, yPos - 10), null, _players[i].Color, _players[i].Angle, cannonOrigin, _playerScaling, SpriteEffects.None, 1);
}
}
}
private void DrawText()
{
PlayerData player = _players[_currentPlayer];
int currentAngle = (int)MathHelper.ToDegrees(player.Angle);
_spriteBatch.DrawString(_font, "Cannon angle: " + currentAngle.ToString(), new Vector2(20, 20), player.Color);
_spriteBatch.DrawString(_font, "Cannon power: " + player.Power.ToString(), new Vector2(20, 45), player.Color);
}
private void DrawRocket()
{
if (_rocketFlying)
{
_spriteBatch.Draw(_rocketTexture, _rocketPosition, null, _players[_currentPlayer].Color, _rocketAngle, new Vector2(42, 240), _rocketScaling, SpriteEffects.None, 1);
}
}
private void DrawSmoke()
{
for (int i = 0; i < _smokeList.Count; i++)
{
_spriteBatch.Draw(_smokeTexture, _smokeList[i], null, Color.White, 0, new Vector2(40, 35), 0.2f, SpriteEffects.None, 1);
}
}
}
}