scrolling background in xna

background

using System;

using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Audio;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
using Microsoft.Xna.Framework.Storage;
namespace Tetris_Shooter
{
   public class ScrollingBackground
   {
      // class ScrollingBackground
      private Vector2 screenpos, origin, texturesize;
      private Texture2D mytexture;
      private int screenheight;
      public void Load(GraphicsDevice Device, Texture2D BackgroundTexture)
      {
         mytexture = BackgroundTexture;
         screenheight = Device.Viewport.Height;
         int screenwidth = Device.Viewport.Width;
         // Set the origin so that we're drawing from the 
         // center of the top edge.
         origin = new Vector2(mytexture.Width / 2, 0);
         // Set the screen position to the center of the screen.
         screenpos = new Vector2(screenwidth / 2, screenheight / 2);
         // Offset to draw the second texture, when necessary.
         texturesize = new Vector2(0, mytexture.Height);
      }
      // ScrollingBackground.Update
      public void Update(float deltaY)
      {
         screenpos.Y += deltaY;
         screenpos.Y = screenpos.Y % mytexture.Height;
      }
      // ScrollingBackground.Draw
      public void Draw(SpriteBatch Batch)
      {
         // Draw the texture, if it is still onscreen.
         if (screenpos.Y < screenheight)
         {
            Batch.Draw(mytexture, screenpos, null,
                 Color.White, 0, origin, 1, SpriteEffects.None, 0f);
         }
         // Draw the texture a second time, behind the first,
         // to create the scrolling illusion.
         Batch.Draw(mytexture, screenpos - texturesize, null,
              Color.White, 0, origin, 1, SpriteEffects.None, 0f);
      }
   }
}