Libgdx , When to use camera.position.set? - libgdx

Question

I am really confused with two examples related to viewport and orthagraphic. Although i understand that Viewport is the size of the dimensions we set to view on the screen and camera projects that. I am learning libgdx and cannot finish through orthographic camera and viewport examples which have left me completely confused. the code runs fine for both examples and with proper result on screen.
here's one example in which camera.position.set is used to position the camera.
public class AnimatedSpriteSample extends GdxSample {
private static final float WORLD_TO_SCREEN = 1.0f / 100.0f;
private static final float SCENE_WIDTH = 12.80f;
private static final float SCENE_HEIGHT = 7.20f;
private static final float FRAME_DURATION = 1.0f / 30.0f;
private OrthographicCamera camera;
private Viewport viewport;
private SpriteBatch batch;
private TextureAtlas cavemanAtlas;
private TextureAtlas dinosaurAtlas;
private Texture background;
private Animation dinosaurWalk;
private Animation cavemanWalk;
private float animationTime;
#Override
public void create() {
camera = new OrthographicCamera();
viewport = new FitViewport(SCENE_WIDTH, SCENE_HEIGHT, camera);
batch = new SpriteBatch();
animationTime = 0.0f;
...
...
..
camera.position.set(SCENE_WIDTH * 0.5f, SCENE_HEIGHT * 0.5f, 0.0f);
Here's another example which does not use camera.position.set and still the result is the same.
#Override
public void create() {
camera = new OrthographicCamera();
viewport = new FitViewport(SCENE_WIDTH, SCENE_HEIGHT, camera);
batch = new SpriteBatch();
oldColor = new Color();
cavemanTexture = new Texture(Gdx.files.internal("data/caveman.png"));
cavemanTexture.setFilter(TextureFilter.Nearest, TextureFilter.Nearest);
}
#Override
public void dispose() {
batch.dispose();
cavemanTexture.dispose();
}
#Override
public void render() {
Gdx.gl.glClearColor(BACKGROUND_COLOR.r,
BACKGROUND_COLOR.g,
BACKGROUND_COLOR.b,
BACKGROUND_COLOR.a);
Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
batch.setProjectionMatrix(camera.combined);
batch.begin();
int width = cavemanTexture.getWidth();
int height = cavemanTexture.getHeight();
float originX = width * 0.5f;
float originY = height * 0.5f;
// flipX, flipY
// Render caveman centered on the screen
batch.draw(cavemanTexture, // Texture itselft
-originX, -originY, // pass in the world space coordinates where we to draw, Considering the camera is centered at (0,0). by default we need to position
// out cavement at -originX, -originY.
originX, originY, // coordinates in pixels of our texture that we consider to be the origin starting from the bottom-left corner.
// in our case, we want the origin to be the center of the texture. then we pass the dimensions of the texture and the scale
// and the scale along both axes (x and Y).
width, height, // width, height
WORLD_TO_SCREEN, WORLD_TO_SCREEN, // scaleX, scaleY
0.0f, // rotation
0, 0, // srcX, srcY
width, height, // srcWidth, srcHeight
false, false); // flipX, flipY
What is really confusing me is why does it not use camera.position.set on the second example to adjust the camera's view and why is it important to use this on the first example.
I really hope this question is legit and makes sense. I have searched the forum here and couldnt find any clues. Hope someone can guide in the right direction.
Many Thanks.

Answer 1

In the first example a 2 dimensional vector has been initialized for the position of the camera the x direction and the y direction. This for the specifically the camera.
camera = new OrthographicCamera();
So, this code creates a camera object from the OrthographicCamera class created by libgdx creators. Check out the documentation for the class here from that class you can see when that it is constructed it accepts both the viewport_height and viewport_width. (in your example you've left it blank, so these are 0 for the time being.)
viewport = new FitViewport(SCENE_WIDTH, SCENE_HEIGHT, camera);
This line of code defines the width, height and which camera should be used for the viewport. check out the documentation for FitViewport class here
So when camera.position.set is called, it sets for the x and y direction based on the viewport's width and height. This whole example defines the viewport dimensions for the overall viewport.
The difference between this and the second example is that the camera is set around the texture that has been loaded onto the screen. So the viewport's x and y direction has been positioned and the width, height, originX, originY of the texture/camera has been defined also:
int width = cavemanTexture.getWidth();
int height = cavemanTexture.getHeight();
float originX = width * 0.5f;
float originY = height * 0.5f;
Libgdx then allows you to draw the texture using the spritebatch class to draw both the texture and the viewport surrounding that texture.
Summary
Example one allows you to define a viewport on it's own, without any textures being drawn. This will allow you to draw multiple textures with the same viewport being set (a normal process of game creation)
But in Example two if you wanted the viewport to say, follow the main character around on the screen. you can define the viewport surrounding the texture to thus follow that texture.
Personally, i'd always pursue the first example as you can define a viewport for any game width or height and then i'd create a second viewport ontop to follow any textures i've drawn on the screen. They both work, just for different reasons.
Hope this helps you clear things up.
Happy coding,
Bradley.