Changing the Coordinate System in LibGDX (Java)

Just to expand a little on what badlogic said above, if you are using a TextureAtlas (with TextureRegions) you need to flip them, as badlogic said, in addition to the camera work. If you are using a TextureAtlas, you can use this code right after loading your atlas:

String textureFile = "data/textures.txt";  
atlas = new TextureAtlas(Gdx.files.internal(textureFile), Gdx.files.internal("data"));  
// Let's flip all the regions.  Required for y=0 is TOP
Array<AtlasRegion> tr = atlas.getRegions();      
for (int i = 0; i < tr.size; i++) {
  TextureRegion t = tr.get(i);
  t.flip(false, true);
}

If you use a Camera (which you should) changing the coordinate system is pretty simple:

camera= new OrthographicCamera(Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
camera.setToOrtho(true, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());

If you use TextureRegions and/or a TextureAtlas, all you need to do in addition to that is call region.flip(false, true).

The reasons we use y-up by default (which you can easily change as illustrated above) are as follows:

• your simulation code will most likely use a standard euclidian coordinate system with y-up
• if you go 3D you have y-up
• The default coordinate system is a right handed one in OpenGL, with y-up. You can of course easily change that with some matrix magic.

The only two places in libgdx where we use y-down are:

• Pixmap coordinates (top upper left origin, y-down)
• Touch event coordinates which are given in window coordinates (top upper left origin, y-down)

Again, you can easily change the used coordinate system to whatever you want using either Camera or a tiny bit of matrix math.