Relative mouse tracking stick mouse to center of screen

Question

I wrote this code to handle relative mouse movements,

        public override void Update(GameTime gt)
        {
            _lastmousestate = _mousestate;
            _mousestate = Mouse.GetState();
            if(LockMouse)
                Mouse.SetPosition(EntityGame.Viewport.Width/2,EntityGame.Viewport.Height/2);
            Point distance = new Point(_lastmousestate.X - _mousestate.X, _lastmousestate.Y - _mousestate.Y);
            Cursor.Position = new Point(Cursor.Position.X - distance.X, Cursor.Position.Y - distance.Y);
        }

Cursor is the cursor drawn to the screen to track the mouse. When running this code my mouse sticks to the center of the screen and won't move. However, the X,Y values change for a second before resetting back to the center of the screen.

Any ideas?

EDIT: Setting LockMouse to false causes the mouse and cursor to act perfectly fine although it is not bound to the window.

EDIT2: Here is the MouseHandler code, not much to see here just me setting it up so you can bind mouse buttons easier.

using System;
using EntityEngineV4.Engine;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;

namespace EntityEngineV4.Input.MouseInput
{
    public class MouseHandler : Service
    {
        public CursorEntity CursorEntity;
        private static MouseState _mousestate;
        public static MouseState MouseState {
            get { return _mousestate;}
        }
        private static MouseState _lastmousestate;
        public static MouseState LastMouseState {
            get { return _lastmousestate;}
        }

        public bool LockMouse = false;

        public MouseHandler (EntityState stateref) : base(stateref)
        {
            CursorEntity = new CursorEntity(stateref, stateref, "CursorEntity", this);
            stateref.AddEntity(CursorEntity);
        }

        public override void Update(GameTime gt)
        {
            _lastmousestate = _mousestate;
            _mousestate = Mouse.GetState();
            if (_lastmousestate == _mousestate) return; //The mouse was the same, no need to do anything.
            if(LockMouse)
                Mouse.SetPosition(EntityGame.Viewport.Width/2,EntityGame.Viewport.Height/2);
            Point distance = new Point(_lastmousestate.X - _mousestate.X, _lastmousestate.Y - _mousestate.Y);
            CursorEntity.Position = new Point(CursorEntity.Position.X - distance.X, CursorEntity.Position.Y - distance.Y);
        }

        public override void Draw(SpriteBatch sb)
        {
        }

        public Point GetPositon()
        {
            return new Point(_mousestate.X, _mousestate.Y);
        }

        public void SetPositon(Point p)
        {
            Mouse.SetPosition(p.X, p.Y);
        }

        public void Flush()
        {
            _lastmousestate = _mousestate;
        }

        public bool IsMouseButtonDown(MouseButton mb)
        {
            switch(mb)
            {
            case MouseButton.LeftButton:
                return _mousestate.LeftButton == ButtonState.Pressed;
            case MouseButton.MiddleButton:
                return _mousestate.MiddleButton == ButtonState.Pressed;
            case MouseButton.RightButton:
                return _mousestate.RightButton == ButtonState.Pressed;
            case MouseButton.XButton1:
                return _mousestate.XButton1 == ButtonState.Pressed;
            case MouseButton.XButton2:
                return _mousestate.XButton2 == ButtonState.Pressed;
            }
            throw new Exception("MouseButton does not exist!");
        }

        public bool IsMouseButtonPressed (MouseButton mb)
        {
            switch (mb) 
            {
            case MouseButton.LeftButton:
                return _mousestate.LeftButton == ButtonState.Pressed && _lastmousestate.LeftButton == ButtonState.Released;
            case MouseButton.RightButton:
                return _mousestate.RightButton == ButtonState.Pressed && _lastmousestate.RightButton == ButtonState.Released;
            case MouseButton.MiddleButton:
                return _mousestate.MiddleButton == ButtonState.Pressed && _lastmousestate.MiddleButton == ButtonState.Released;
            case MouseButton.XButton1:
                return _mousestate.XButton1 == ButtonState.Pressed && _lastmousestate.XButton1 == ButtonState.Released;
            case MouseButton.XButton2:
                return _mousestate.XButton2 == ButtonState.Pressed && _lastmousestate.XButton2 == ButtonState.Released;
            }
            throw new Exception("MouseButton does not exist!");
        }

        public bool IsMouseButtonUp(MouseButton mb)
        {
            switch(mb)
            {
            case MouseButton.LeftButton:
                return _mousestate.LeftButton == ButtonState.Released;
            case MouseButton.MiddleButton:
                return _mousestate.MiddleButton == ButtonState.Released;
            case MouseButton.RightButton:
                return _mousestate.RightButton == ButtonState.Released;
            case MouseButton.XButton1:
                return _mousestate.XButton1 == ButtonState.Released;
            case MouseButton.XButton2:
                return _mousestate.XButton2 == ButtonState.Released;
            }
            throw new Exception("MouseButton does not exist!");
        }

        public bool IsMouseButtonReleased (MouseButton mb)
        {
            switch (mb) 
            {
            case MouseButton.LeftButton:
                return _mousestate.LeftButton == ButtonState.Released && _lastmousestate.LeftButton == ButtonState.Pressed;
            case MouseButton.RightButton:
                return _mousestate.RightButton == ButtonState.Released && _lastmousestate.RightButton == ButtonState.Pressed;
            case MouseButton.MiddleButton:
                return _mousestate.MiddleButton == ButtonState.Released && _lastmousestate.MiddleButton == ButtonState.Pressed;
            case MouseButton.XButton1:
                return _mousestate.XButton1 == ButtonState.Released && _lastmousestate.XButton1 == ButtonState.Pressed;
            case MouseButton.XButton2:
                return _mousestate.XButton2 == ButtonState.Released && _lastmousestate.XButton2 == ButtonState.Pressed;
            }
            throw new Exception("MouseButton does not exist!");
        }
    }

    public enum MouseButton
    {
        LeftButton, RightButton, MiddleButton, XButton1, XButton2
    }
}

Answer 1

Figured it out.

You have to ignore the last mouse state when the mouse is locked and just set it to the center of the screen like so.

            public override void Update(GameTime gt)
        {
            Flush();
            _mousestate = Mouse.GetState();

            if (LockMouse)
            {
                int lockx = EntityGame.Viewport.Width/2;
                int locky = EntityGame.Viewport.Height/2;

                //After we get our states, we can reset the Mouse with no problems!
                SetPosition(lockx, locky);
                Point distance = new Point(lockx - _mousestate.X, locky - _mousestate.Y);
                CursorEntity.Position = new Point(CursorEntity.Position.X - distance.X, CursorEntity.Position.Y - distance.Y);
            }
            else
            {
                //Calc our distance and add it to our cursor.
                Point distance = new Point(_lastmousestate.X - _mousestate.X, _lastmousestate.Y - _mousestate.Y);
                CursorEntity.Position = new Point(CursorEntity.Position.X - distance.X, CursorEntity.Position.Y - distance.Y);
            }
            CursorEntity.Update(gt);
        }