public const TerminalVelocity = 60;
public const Gravity = 20; 

public class JumpObject
{
    //Current Location
    private Vector2 _Location = Vector.Zero;
    private Vector2 _Velocity = Vector.Zero;
   
    //Occurs when user wants object to jump.
    public void Jump(float Speed) {
       //Check if the hes already jumping, if not apply jump
       if (_Velocity.Y == 0)
          _Velocity.Y = Speed;
    }
   
    //Occurs when they want to move right
    public void MoveRight(float Speed) {
       _Velocity.X = Speed;
       if (_Velocity.Y == 0)
          //Flip Sprite here if Sprite is not already pointing right  (you can check this by checking if _Velocity.X is positive)
    }

    //Occurs when the want to move left
    public void MoveLeft(float Speed) {
       _Velocity.X = Speed;
       if (_Velocity.Y == 0)
           //Flip Sprite here if Sprite is not already pointing right  (you can check this by checking if _Velocity.X is negative)
    }

    //Update every frame
    public void Update(GameTime gameTime) {
       //Time in seconds since last update
       float Deltatime = gameTime.ElapsedGameTime.TotalSeconds;
       //Actual Speed of the falling object
       Vector2 Speed = new Vector2(_Velocity.X, _Velocity.Y + Gravity);
       //Check if its falling faster than its terminal velocity
       if (Speed.Y > TerminalVelocity)
          Speed.Y = TerminalVelocity;
       //Increase location by velocity and gravity
       _Location += Speed * Deltatime;
       //Check to see if the object is jumping
       if (_Velocity.Y != 0) {
	  //Get the Height of land where the object is above
          float CurrentHeight = GetHeight(_Location.X, _Location.Y);
          //If the object is below the terrain set it to the correct level and set velocity to zero
          if (_Location.Y <= CurrentHeight) {
             _Velocity = Vector2.Zero;
             _Location.Y = CurrentHeight;
          }
       }
    }
}

public class Link
{
    //Constants
    //=Change these to mod Link's jump
    //=If you increase Gravity and JumpSpeed proportionately then 
    //  he will jump faster but still achieve the same height.
    //=If you decrease the gravity he will jump higher but could 
    //  get unwated air time so increase gravity by some and 
    //  Jumpspeed by alot more.
    public const float Gravity = 100;
    public const float TerminalVelocity = -250;
    public const float JumpSpeed = 200;
    //Variables
    public Vector3 Position = Vector3.Zero;
    public Vector3 MoveVector = Vector3.Zero;
    public float UpwardVelocity = 0f;
    public float Rotation = 0f;
    public Matrix WorldMatrix = Matrix.Identity;
    //Functions
    public void MoveForward() { } //Code here
    public void MoveBackward() { } //Code here
    public void RotateLeft() { } //Code here
    public void RotateRight() { } //Code here
    public void StrafeLeft() { } //Code here
    public void StrafeRight() { } //Code here
    //Jump method
    public void Jump() {
        //Makes sure Link isn't already in the air
        if (!InAir) {
            UpwardVelocity = JumpSpeed;
            InAir = true;
        }
    }
    //Calls on every frame with '(float)gameTime.ElapsedGameTime.TotalSeconds' as Deltatime
    public void Update(float Deltatime) {
        if (InAir) {
            //Since Link is jumping increase his vertical position by Upwardvelocity
            Position.Y += UpwardVelocity * Deltatime;
            //Apply Gravity to UpwardVelocity so Link falls back down
            UpwardVelocity -= Gravity * Deltatime;
            //Restrain Link from falling faster then TerminalVelocity
            if (UpwardVelocity < TerminalVelocity)
                UpwardVelocity = TerminalVelocity;
            //Get the CurrentHeight of the Land below Link
            float CurrentHeight = GetHeight(Position.X, Position.Y);
            //Check if Link is below or equal to the landheight, 
            //if so then stop him from jumping and reset him to the terrain
            if (Position.Y <= CurrentHeight) {
                UpwardVelocity = 0f;
                Position.Y = CurrentHeight;
            }
        }
    }
    //Used to determine if hes jumping
    public bool InAir
    {
        get { return (UpwardVelocity != 0); }
    }
}