title: what is source rectangle in spritebatch.draw in xna
body: <p>What is the purpose of the source rectangle parameter in the SpriteBatch.Draw() method?</p>
  
  <p>MSDN says: <code>A rectangle that specifies (in texels) the source texels from a texture. Use null to draw the entire texture.</code></p>
  
  <p>What does that mean?</p>