/// <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);
GraphicsDevice.BlendState = BlendState.Opaque;
GraphicsDevice.DepthStencilState = DepthStencilState.Default;
effect.View = camera.ViewMatrix;
effect.World = Matrix.Identity;
effect.CurrentTechnique.Passes[0].Apply();
Matrix identity = Matrix.Identity;
ground.Draw(effect);
airplane.Draw(ref effect, ref identity);
houses.Draw(effect);
base.Draw(gameTime);
}