XNA mouse coords vs objects problem

Question

Hi all,

I'm having a problem with the xna framework, I have a stripped down version of my code here to demonstrate. When the mouse is clicked an object is created at that mouse click point and the object is displayed via it's own draw method.

What happens is that the first object is created at the correct position (current mouse coords are displayed as text) but when the first object is created then the current mouse coords are offset relative to the window position. Subsequent creation of objects offsets it again until I get a pretty diagonal of object across the screen. If I remove the mthod to create the object then all is well -mouse coords remain good relative to the window.

Here's the code, there are the base methods, a method to create an object, a class for the object and a class to find mouse inout. Has anyone else had this problem or can see what I'm doing wrong?

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;
using Microsoft.Xna.Framework.Net;
using Microsoft.Xna.Framework.Storage;

namespace mousetest
{
/// <summary>
/// This is the main type for your game
/// </summary>
public class Game1 : Microsoft.Xna.Framework.Game
{
    GraphicsDeviceManager graphics;
    SpriteBatch spriteBatch;
    public SpriteFont defaultFont;

    public static Vector2 mousepos;

    public Texture2D anobjectTexture;

    public List<anobject> anobjectList = new List<anobject>();

    public Game1()
    {
        graphics = new GraphicsDeviceManager(this);
        Content.RootDirectory = "Content";
    }

    /// <summary>
    /// Allows the game to perform any initialization it needs to before starting to run.
    /// This is where it can query for any required services and load any non-graphic
    /// related content.  Calling base.Initialize will enumerate through any components
    /// and initialize them as well.
    /// </summary>
    protected override void Initialize()
    {
        // TODO: Add your initialization logic here

        //make the mouse pointer visible 
        this.IsMouseVisible = true;

        base.Initialize();
    }

    /// <summary>
    /// LoadContent will be called once per game and is the place to load
    /// all of your content.
    /// </summary>
    protected override void LoadContent()
    {
        // Create a new SpriteBatch, which can be used to draw textures.
        spriteBatch = new SpriteBatch(GraphicsDevice);

        // TODO: use this.Content to load your game content here

        defaultFont = Content.Load<SpriteFont>(@"fonts\arial");

        anobjectTexture = Content.Load<Texture2D>("reddot");
    }

    /// <summary>
    /// UnloadContent will be called once per game and is the place to unload
    /// all content.
    /// </summary>
    protected override void UnloadContent()
    {
        // TODO: Unload any non ContentManager content here
    }

    /// <summary>
    /// Allows the game to run logic such as updating the world,
    /// checking for collisions, gathering input, and playing audio.
    /// </summary>
    /// <param name="gameTime">Provides a snapshot of timing values.</param>
    protected override void Update(GameTime gameTime)
    {
        // Allows the game to exit
        if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
            this.Exit();

        // TODO: Add your update logic here

        mouseUpdate();

        base.Update(gameTime);
    }

    /// <summary>
    /// This is called when the game should draw itself.
    /// </summary>
    /// <param name="gameTime">Provides a snapshot of timing values.</param>
    protected override void Draw(GameTime gameTime)
    {
        GraphicsDevice.Clear(Color.CornflowerBlue);

        // TODO: Add your drawing code here

        //draw the mouse coords
        //Draw the debug text 
        //
        spriteBatch.Begin(SpriteBlendMode.AlphaBlend, SpriteSortMode.FrontToBack, SaveStateMode.None);

        spriteBatch.DrawString(defaultFont, "mousex: " + mousepos.X + " mousey: " +mousepos.Y,
            new Vector2(10, 10), Color.Black, 0, Vector2.Zero, 1, SpriteEffects.None, 1);


        int i = 0;
        foreach (anobject theobject in anobjectList)
        {
            theobject.drawObject(spriteBatch);
            i++;
        }

        spriteBatch.DrawString(defaultFont, "objects: " + i,
        new Vector2(10, 20), Color.Black, 0, Vector2.Zero, 1, SpriteEffects.None, 1);

        spriteBatch.End();

        base.Draw(gameTime);
    }

    //mouse test method
    public Vector2 mouseUpdate()
    {
        MouseInput.CheckMouse(800, 600);
        mousepos.X = MouseInput.mouseState.X;
        mousepos.Y = MouseInput.mouseState.Y;

        if (MouseInput.ismouse_leftbuttonpressed == 1)
        {
            if (MouseInput.ismouse_leftbuttonheld == 0)
            {
                doSomething();
            }
        }

        return mousepos;
    }


    public void doSomething()
    {
        //create an instance of the 'anobject' class when the mouse is clicked

        anobject testobject = new anobject(mousepos, anobjectTexture);
        anobjectList.Add(testobject);

    }
}


public class anobject : Game1
{
    public Vector2 position;
    public Texture2D anobjectTexture;

    //constructor
    public anobject(Vector2 inpos, Texture2D inTexture)
    {
        position = inpos;
        anobjectTexture = inTexture;

    }

    public void drawObject(SpriteBatch inspritebatch)
    {

        inspritebatch.Draw(anobjectTexture,
                    new Vector2(
                    (position.X),
                    (position.Y)),
                    null, Color.White, 0, Vector2.Zero, 1, SpriteEffects.None, 0.99f); 
    }

    }//end of class
}


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Xna.Framework.Input;
using Microsoft.Xna.Framework;

namespace mousetest
{
    class MouseInput: Game1
    {
        public static MouseState mouseState;

        // might need this just cause the way the api mouse call works  
        public static Vector2 mouseLocation;
        // these are Mouse position values  
        public static int mousePosition_X = 0;
        public static int mousePosition_Y = 0;
        public static float virt_mousePosition_X = 0.0f; // this is calculated to were the mouse is as a percentage of screen width height  
        public static float virt_mousePosition_Y = 0.0f; // this is very useful for seting positions of boxes and buttons ect...  
        // left mouse button  
        public static int ismouse_leftbuttonpressed = 0; // is left being pressed at this moment  
        public static int leftmouselastpressedatX = 0;
        public static int leftmouselastpressedatY = 0;
        public static int leftmouselastdragreleasedX = 0;
        public static int leftmouselastdragreleasedY = 0;
        public static int ismouse_leftbuttonheld = 0; // is left being held down  
        // right mouse button  
        public static int ismouse_rightbuttonpressed = 0; // is right being pressed at this moment  
        public static int rightmouselastpressedatX = 0;
        public static int rightmouselastpressedatY = 0;
        public static int rightmouselastdragreleasedX = 0;
        public static int rightmouselastdragreleasedY = 0;
        public static int ismouse_rightbuttonheld = 0;  // is right being held down  
        // this is the scroll wheel  
        public static int mousewheel_value = 0; // this will mainly affect the zoomvalue its multiplyed by a small number to get the below  
        public static int mouseoldwheel_value = 0;
        public static float zoomwheel_value = 0; // this is a value that relects the % of zoom  
        public static float zoomvalue = 1.0F; // this we modify later on for mouse scrolling zooming  


        /// <summary>  
        /// one lil problem this is still in this function SGMKS.screenWidth; so ill have to deal with that later on  
        /// as the screen size might change and thus ruin alot of info if we dont update that  
        ///   
        ///  get the mouse values and save them into a static class to track those variables  
        /// </summary>  
        public static void CheckMouse(int sW, int sH)
        {
            // grab the mouse state from the input class  
            mouseState = Mouse.GetState();
            // save the current mouse position into another variable for later use  
            mousePosition_X = mouseState.X;
            mousePosition_Y = mouseState.Y;
            virt_mousePosition_X = (float)mousePosition_X / (float)sW;
            virt_mousePosition_Y = (float)mousePosition_Y / (float)sH;
            // or we could put this in a vector instead  
            mouseLocation = new Vector2(mousePosition_X, mousePosition_Y);

            // Processing when carrying out the left click of the mouse  
            //_______________________________________________  
            if (mouseState.LeftButton == ButtonState.Pressed)
            {
                //NOTE THESE ARE PLACED IN A SPECIFIC ORDER TO ENSURE THAT DRAG CLICK LOGIC IS CORRECT  
                // Never *** it up note to self thanks  
                // on the first pass the below will set the lastposmousepressed to the current position  
                if (ismouse_leftbuttonheld == 0) // this executes on the first pass and the second pass but not the third pass  
                {
                    if (ismouse_leftbuttonpressed == 1) // this condition will not execute untill the second pass thru the function  
                    {
                        ismouse_leftbuttonheld = 1; // now we mark it as being held on the second pass                         
                    }
                    else  // this executes on the first pass only  
                    {
                        leftmouselastpressedatX = mousePosition_X; // and we save the click of the first point of holding   
                        leftmouselastpressedatY = mousePosition_Y; // so when released we know were we draged from  
                    }
                }
                // set at the end of but still in the first pass  
                ismouse_leftbuttonpressed = 1;// we SET this after the call to is leftbutton pressed now to to ensure next pass its active  
            }
            else
            { // mouse itself is no longer registering the button pressed so.. toggle held and button pressed off  
                ismouse_leftbuttonpressed = 0;
                if (ismouse_leftbuttonheld == 1)
                {
                    leftmouselastdragreleasedX = mousePosition_X;
                    leftmouselastdragreleasedY = mousePosition_Y;
                }
                ismouse_leftbuttonheld = 0;
            }

            // Processing when carrying out the right click of the mouse  
            //________________________________________________  
            if (mouseState.RightButton == ButtonState.Pressed)
            {
                //NOTE THESE ARE PLACED IN A SPECIFIC ORDER TO ENSURE THAT DRAG CLICK LOGIC IS CORRECT  
                // on the first pass the below will set the lastposmousepressed to the current position  
                if (ismouse_rightbuttonheld == 0) // this executes on the first pass and the second pass but not the third pass  
                {
                    if (ismouse_rightbuttonpressed == 1) // this condition will not execute untill the second pass thru the function  
                    {
                        ismouse_rightbuttonheld = 1; // now we mark it as being held on the second pass  
                    }
                    else  // this executes on the first pass only  
                    {
                        rightmouselastpressedatX = mousePosition_X; // and we save the click of the first point of holding   
                        rightmouselastpressedatY = mousePosition_Y; // so when released we know were we draged from  
                    }
                }
                // set at the end of the first pass  
                ismouse_rightbuttonpressed = 1;// we SET this after the call to is rightbutton pressed now to to ensure next pass its active  
            }
            else
            { // right mouse button itself is no longer registering the button pressed so.. toggle held and button pressed off  
                ismouse_rightbuttonpressed = 0;
                if (ismouse_rightbuttonheld == 1)
                {
                    rightmouselastdragreleasedX = mousePosition_X;
                    rightmouselastdragreleasedY = mousePosition_Y;
                }
                ismouse_rightbuttonheld = 0;
            }

        }//endof method  


    }
}

Answer 1

Your MouseInput and AnObject classes are descending from your Game1 class, so each time you create an instance of AnObject you're creating a Game instance.

Part of Mouse.GetState() looks like this:

if (hHookedHandle != null)
{
    ScreenToClient(hHookedHandle, &gpoint);
}

So, without looking into it too much more deeply, the Game class is converting mouse screen coordinates to window coordinates. So each time you create a new Game instance it's likely a child of the previous instance so its window coordinates are within its parent instance.

The solution is to remove the ": Game1" from your classes. You generally only want to have a single Game class in your project.