title: Understand LibGDX Coordinate system and drawing sprites
body: <p>So I am super stoked to start using LibGDX for my first android title for OUYA and PC, but I am running into some snags with LibGDX. (All of my questions can be answered by looking at source, but I am really trying to understand the design choices as well).</p>
  
  <p>To start with, the coordinate system. I created a project using the Project Setup jar, and it creates an OrthographicCamera like so</p>
  
  <pre><code>camera = new OrthographicCamera(1, h/w);
  </code></pre>
  
  <p>From my reading, I understand that LibGdx uses bottom left corner for 0,0 and yUp. Fine.
  I see that it is pretty easy to change to y down if I want to, but I am not understanding the next bit of code that was created.</p>
  
  <p>For the default sprite that gets created the position is set like so.</p>
  
  <pre><code>logoSprite.setOrigin(logoSprite.getWidth()/2, logoSprite.getHeight()/2);
  logoSprite.setPosition(-logoSprite.getWidth()/2, -logoSprite.getHeight()/2);
  </code></pre>
  
  <p>When I run this basic program, I see the logo image I have added is centered on the screen. What I am trying to understand is why the values are negative in set position, and why is it using the sprite width and height instead of the graphics w and h of the view port? If I change to the screen width and height, then the image is drawn in some odd position in the lower right hand side of the screen. </p>
  
  <p>My next question is sprite.setSize vs sprite.setScale. Why is the difference between the two? (They appear to do the same thing, except setScale leaves getWidth and getHeight unchanged).</p>
  
  <p>Since my game will be using a 2D camera heavily for panning, zooming and rotation, I am trying to understand as much as I can about the libgdx framework before I start writing any code.</p>
  
  <p>As a side note, I have a game development and math background and I have made several 2D and 3D games using XNA. I am finding LibGdx a bit frustrating as it does not abstract away OpenGL as much as I was expecting it to, and so far the 2D drawing I have been experimenting with seems to be more confusing than it should be!</p>
  
  <p>I also wanted to note that I am planning to use spine for my animations. Should that change my choice to use y-up or y-down?</p>