Small project to show drawing items with the mouse in XNA
I saw a post today on the XNA Community Forums asking how to give a player the possibility of adding things to a game, and storing the position of the added images.
I made a 
little project to show how to do this. Basically it adds a Vector2 to a generic List when the left mouse button is pressed and removes a Vector2 when the right mousebutton is pressed.
Here's a small demo:
using System.Collections.Generic;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
namespace SmallXNADrawingGame
{
/// <summary>
/// Small class to show how to be able to draw and store objects in XNA.
///
/// Jakob "XNAFAN" Krarup - February 2010
/// http://www.xnafan.net
/// </summary>
public class Game1 : Microsoft.Xna.Framework.Game
{
GraphicsDeviceManager graphics;
SpriteBatch spriteBatch;
//a list to store the dots in
List<Vector2> positionOfDots = new List<Vector2>();
//the dot to use for drawing
Texture2D textureDot;
//stores half the size of the dot for centering the texture
Vector2 halfSizeOfDot;
//stores the current and previous states of the mouse
//they are used to compare in Update() to make sure
//a mouseclick is a new one and not just the button being held
MouseState currentMouse, oldMouse;
//font for writing instructions
SpriteFont defaultFont;
public Game1()
{
graphics = new GraphicsDeviceManager(this);
//set size of screen
graphics.PreferredBackBufferHeight = 600;
graphics.PreferredBackBufferWidth = 800;
Content.RootDirectory = "Content";
//make sure to display mouse cursor
this.IsMouseVisible = true;
}
protected override void LoadContent()
{
// Create a new SpriteBatch, which can be used to draw textures.
spriteBatch = new SpriteBatch(GraphicsDevice);
textureDot = Content.Load<Texture2D>("dot");
//calculate half the size of a dot and store it
//for drawing the dot centered on the mouseclick (se Draw())
halfSizeOfDot = new Vector2(textureDot.Width / 2, textureDot.Height / 2);
//load the font
defaultFont = Content.Load<SpriteFont>("DefaultFont");
}
protected override void Update(GameTime gameTime)
{
//store the current state of the mouse (buttons, position, etc.)
currentMouse = Mouse.GetState();
//if the mousebutton was pressed between this and last update...
//this check makes certain that one click doesn't create multiple dots because the button is held down
if (currentMouse.LeftButton == ButtonState.Pressed && oldMouse.LeftButton == ButtonState.Released)
{
positionOfDots.Add(new Vector2(currentMouse.X, currentMouse.Y));
}
//if right mousebutton was pressed
if (currentMouse.RightButton == ButtonState.Pressed && oldMouse.RightButton == ButtonState.Released)
{
//and there are still dots left
if (positionOfDots.Count > 0)
{
//remove the last
//"-1" is because the list i zero-indexed,
//so a count of 1 would remove the dot at position 1-1 (zero).
positionOfDots.RemoveAt(positionOfDots.Count - 1);
}
}
base.Update(gameTime);
//store the current state in oldMouse
//to be able to determine when buttons have JUST been pressed
//by comparing the two states in an update
oldMouse = currentMouse;
}
protected override void Draw(GameTime gameTime)
{
GraphicsDevice.Clear(Color.CornflowerBlue);
spriteBatch.Begin();
//write instructions
spriteBatch.DrawString(defaultFont, "Left mousebutton to draw dot", new Vector2(20, 20), Color.White);
spriteBatch.DrawString(defaultFont, "Right mousebutton to delete dots", new Vector2(20, 40), Color.White);
foreach (Vector2 position in positionOfDots)
{
//draw the dot centered on the position of the mouse
//by subtracting the Vector
//which has half the textures width for X and half the textures height for Y
//from the position stored.
spriteBatch.Draw(textureDot, position - halfSizeOfDot, Color.White);
//draw the dot's position
spriteBatch.DrawString(defaultFont, position.ToString(), position, Color.White);
}
base.Draw(gameTime);
spriteBatch.End();
}
}
}
Tags: Beginner, code sample