libGDX - Why do I have to use camera.setToOrtho what does it do?

Question

I am very confused about camera matrices and I don't know where to start my studying. Maybe I have to study OpenGL, but I don't know C++ ...

Ok so I have a camera, Box2d world and a Box2d body.

private World world;
private Box2DDebugRenderer b2dr;
private OrthographicCamera cam;
private Body player;

@Override
public void create () {
    //Create the world without gravity
    world = new World(new Vector2(0, 0), false);
    b2dr = new Box2DDebugRenderer();
    //I create my camera
    cam = new OrthographicCamera();

    //Create the player
    BodyDef bdef = new BodyDef();
    bdef.type = BodyDef.BodyType.DynamicBody;

    //Sets the body position to the center of the screen
    bdef.position.set(Gdx.graphics.getWidth() / 2, Gdx.graphics.getHeight() / 2);

    player = world.createBody(bdef);
    CircleShape shape = new CircleShape();
    shape.setRadius(2f);
    player.createFixture(shape, 1f);
}

@Override
public void render () {
    world.step(1f/60f, 6, 2);

    Gdx.gl.glClearColor(0, 0, 0, 1);
    Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);

    b2dr.render(world, cam.combined);
}

I am not seeing the player on the center of the screen, just a black void.

But if I add cam.setToOrtho(false); I see the player! Why is that?

setToOrtho sets the camera to Orthographic projection WHY?

The camera is Orthographic what oder projection can it have?? Isn't the orthographic projection obvious?

Answer 1

setToOrtho does not set the projection type of the camera. An OrthographicCamera will always have an orthographic frustrum.

Looking at the source, it seems to me that setToOrtho is a convenience method to set the viewport size to the screen size and center the camera on the viewport. setToOrtho(false) is showing your character is because your character is within this default viewport that setToOrtho creates.

The reason why you can't see your character without this call, is you never give your camera a viewport size and you never update the camera. Try

cam = new OrthographicCamera(Gdx.graphics.getWidth(), Gdx.graphics.getHeight());

And then every time you change any parameters of your camera, you must call cam.update(); before any draw calls. I usually end up changing the camera so often that I call this every frame.