xnaFan's Blog

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();
        }
    }
}

I had to leave Nordic Game Jam before the votes were counted in the semifinals. Apparently we first made it to the finals and then were picked by the juror Thor Frølich (Graphics Designer and Ninja Extraordinaire from IO Interactive). He liked the simplicity - that the game had one core gameconcept chase and the simplistic graphical expression.
Apparently (I wasn't there, but Rasmus was) suddenly everybody could see the benefits in our simple game as opposed to the graphically superior games
GREAT