Wut?

using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;

namespace TestEnterSb
{
    public class Game1 : Microsoft.Xna.Framework.Game
    {
        GraphicsDeviceManager mGraphics;
        SpriteBatch mSpriteBatch;

        Texture2D mRedSq;
        Texture2D mBlueSq;

        BoundingBox mFirstSq;
        Texture2D mFirstTexSq;

        BoundingBox mSecondSq;
        Texture2D mSecondTexSq;

        MouseState mPreviosMouseState;
        MouseState mNewMouseState;
        Vector2 mMousePos;

        int W;
        int H;

        int mResSizeNum = 0;

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

            this.IsMouseVisible = true;

            W = 1024; // GraphicsAdapter.DefaultAdapter.CurrentDisplayMode.Width;
            H = 768; // GraphicsAdapter.DefaultAdapter.CurrentDisplayMode.Height;

            mGraphics.PreferredBackBufferWidth = W;
            mGraphics.PreferredBackBufferHeight = H;
            //mGraphics.IsFullScreen = true;

            Mouse.WindowHandle = Window.Handle;
        }

        protected override void Initialize()
        {
            mFirstSq = new BoundingBox(new Vector3(100, 100, 0), new Vector3(200, 200, 0));
            mSecondSq = new BoundingBox(new Vector3(W - 100, H - 100, 0), new Vector3(W, H, 0));

            base.Initialize();
        }

        protected override void LoadContent()
        {
            mSpriteBatch = new SpriteBatch(GraphicsDevice);

            mRedSq = Content.Load<Texture2D>("RedSq");
            mBlueSq = Content.Load<Texture2D>("BlueSq");

            mFirstTexSq = mBlueSq;
            mSecondTexSq = mBlueSq;
        }

        protected override void Update(GameTime Time)
        {
            mPreviosMouseState = mNewMouseState;
            mNewMouseState = Mouse.GetState();

            mMousePos = new Vector2(mNewMouseState.X, mNewMouseState.Y);

            ChangeScrSize();

            if (CheckMouseEnter(mFirstSq)) mFirstTexSq = mRedSq;
            else mFirstTexSq = mBlueSq;

            if (CheckMouseEnter(mSecondSq)) mSecondTexSq = mRedSq;
            else mSecondTexSq = mBlueSq;

            base.Update(Time);
        }

        private void ChangeScrSize()
        {
            if ((mPreviosMouseState.RightButton == ButtonState.Pressed) &&
                (mNewMouseState.RightButton == ButtonState.Released))
            {
                mResSizeNum++;
                if (mResSizeNum > 2) mResSizeNum = 0;

                if (mResSizeNum == 0)
                {
                    mGraphics.PreferredBackBufferHeight = 768;
                    mGraphics.PreferredBackBufferWidth = 1024;
                }
                if (mResSizeNum == 1)
                {
                    mGraphics.PreferredBackBufferHeight = 600;
                    mGraphics.PreferredBackBufferWidth = 800;
                }
                if (mResSizeNum == 2)
                {
                    mGraphics.PreferredBackBufferHeight = 300;
                    mGraphics.PreferredBackBufferWidth = 400;
                }

                mGraphics.ApplyChanges();

                // второй прямоугольник в угол - может вьюпорт надо брать?
                int W = Window.ClientBounds.Width;
                int H = Window.ClientBounds.Height;
                mSecondSq = new BoundingBox(new Vector3(W - 100, H - 100, 0), new Vector3(W, H, 0));
            }
        }


        protected override void Draw(GameTime Time)
        {
            GraphicsDevice.Clear(Color.TransparentBlack);

            mSpriteBatch.Begin();
            mSpriteBatch.Draw(mFirstTexSq, new Vector2(mFirstSq.Min.X, mFirstSq.Min.Y), Color.White);
            mSpriteBatch.Draw(mSecondTexSq, new Vector2(mSecondSq.Min.X, mSecondSq.Min.Y), Color.White);
            mSpriteBatch.End();

            base.Draw(Time);
        }

        private bool CheckMouseEnter(BoundingBox B)
        {
            return (B.Contains(new Vector3(mMousePos.X, mMousePos.Y, 0)) == ContainmentType.Contains);
        }
    }
}