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Libgdx background image not fitting

I am developing a game which has 480x800 VIRTUAL screen sizes. Also I render my map using TiledMapRenderer. My problem is fitting background and HUD elements into the screen which has different ratio than 480/800 (Mostly taller devices). Some devices show blank area at the bottom of screen.
//my viewport (WIDTH = 480, HEIGHT = 800)
viewport = new ScalingViewport(Scaling.fillX,MyGdxGame.WIDTH,MyGdxGame.HEIGHT,camera);
#Override
public void resize(int width, int height) {
viewport.update(width, height, true);
camera.position.set(camera.viewportWidth / 2, camera.viewportHeight / 2, 0);
barriers.getRenderer().setProjectionMatrix(viewport.getCamera().combined);
shapeRenderer.setProjectionMatrix(viewport.getCamera().combined);
}
My screen should fit the X, but background image should fit X and Y without changing the aspect ratio. In this case ScalingViewport does not solve my problem, and if I change the viewport, I have to code everything from beginning.
#Override
public void render(float delta) {
update(delta);
SpriteBatch sb = game.batch;
Gdx.gl.glClearColor(46f/255,46f/255,46f/255,1f);
Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
sb.setProjectionMatrix(camera.combined);
sb.begin();
//this has to change in somehow
sb.draw(AssetManager.backgroundMenu,0,0,MyGdxGame.WIDTH,MyGdxGame.HEIGHT);
sb.end();
}
Should I use multiple viewport? Or is there any way to fit my background into the screen? By the way I do not want to change my camera if there is a way.

Yes, you should use second viewport for your HUD elements.
I would recommend using ExtendViewport
ExtendViewport viewport = new ExtendViewport(MyGdxGame.WIDTH,MyGdxGame.HEIGHT);
It fills all screen (without black bars) and keeps aspect ratio for all resolutions.

positioning a sprite in libgdx

I've got a problem to draw a sprite to my project.
I have a map (960x900) divided into tiles (64x64).
As you can see in the picture, when i click on the bottom left corner of the purple square, the position is (0;0), and when I click on the top right corner of purple square, the position is (36;47)
The problem is that the picture of the purple square has a size of 32x32, and when I draw this picture with libgdx on the screen, the size doesn't match.
Another example: the square with black border has a size of 64x64. So if I draw the purple square in front of the black, the purple should be the half (in height and in width) of the black, no?
Does anyone know why libgdx resizes the purple square?
Sprite sprite = new Sprite(new Texture("assets/purpleSquare.png"));
i draw it in a method
public void render(SpriteBatch batch) {
batch.draw(sprite, 0, 0);
}
I don't know why the picture is resized by libgdx.. I have also tried to do
batch.draw(sprite, 0, 0, width, heigth);
To precise the sprite's size but it doesn't work too..

The size on screen bears no direct relation to the size of the original image. When you draw a sprite you provide the SpriteBatch with a position, width, and height in world coordinates. The sprite will be stretched to fit these world coordinates, regardless of the original image size.
When you click the screen, you are clicking in screen coordinates. The relation between screen and world coordinates is determined by the projection matrix that you use with the SpriteBatch. The projection matrix is typically controlled with a Camera or Viewport object, which you can use to convert between the two coordinate systems using the project and unproject methods.

I'm happy to see that after many hours i found a solution, even if i know which is not correct.
I would like some help to understand the problem's origin.
With this parts of code :
public void update(float delta) {
batch.begin();
drawBackground(); // Draw the background
drawButton(); // Draw the play/pause button
batch.end();
drawMap(); // draw a tmx map made with tiled
batch.begin();
if(!world.isInitial()) {
renderMonster(); // method which draw the monster
}
renderTower(); // method which draw the tower's level
batch.end();
}
I don't understand why i have to do "batch.begin()" and "batch.end()" twice.
I dont' understant why with this code, the purple square is resized.
With this code :
public void update(float delta) {
batch.begin();
drawBackground();
drawButton();
batch.end();
drawMap();
------->sb = new SpriteBatch();
sb.begin();
if(!world.isInitial()) {
renderMonster();
}
renderTower();
sb.end();
}
this line that i add fix the bug with the purple square. If i work with two SpriteBatch (because with one, if i reinitialize SpriteBatch in update method, my pause/play button diseapper) and i initialise the second (SpriteBatch sb) in the update method.
It is correct to initialise a SpriteBatch every time i'm passing on the update method ? There's no method with a SpriteBatch to avoid this problem ?

LibGDX - Centering Orthographic Camera

so I'm working on a game where I would like to have the camera in game centered on the middle of the screen for all device lengths. I hope this picture can better explain what I'm trying to achieve. I have tried setting the position of the camera but that hasn't worked for me.
scrnHeight = Gdx.graphics.getHeight();
if (scrnHeight <= HEIGHT) {
cam.setToOrtho(false, 480, 800);
} else {
cam.setToOrtho(false, 480, scrnHeight);
}
//This is the part that seems to be giving me all the issues
cam.position.set(cam.viewportWidth/2,cam.viewportHeight/2, 0);
cam.update();
Gdx.input.setInputProcessor(this);
Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
gsm.update(Gdx.graphics.getDeltaTime());
gsm.render(batch);
batch.begin();
batch.draw(border, -(border.getWidth() - WIDTH) / 2, -(border.getHeight() / 4));
batch.end();
I don't know if I'm giving it the wrong coordinates when I'm setting the position or what is happening that causes the lack of vertical centering. Any help would be much appreciated.

The orthographic camera position in LibGDX means position in-game, not on the device screen, therefore changing it won't actually move the game screen on the device.
Therefore, you use the camera position to move and position the camera in-game.
For example, in response to player input movement:
if (Gdx.input.isKeyPressed(Input.Keys.LEFT)) {
cam.translate(-3, 0, 0); // Moves the camera to the left.
}
if (Gdx.input.isKeyPressed(Input.Keys.RIGHT)) {
cam.translate(3, 0, 0); // Moves the camera to the right.
}
As you can see, we are moving the camera in-game, left and right according to the player's input.
However, your code has a few more issues like not setting the batch projection matrix:
batch.setProjectionMatrix(cam.combined);
And resetting the camera position to the center of the viewport each frame:
// Don't run this each frame, it resets the camera position!
cam.position.set(cam.viewportWidth/2,cam.viewportHeight/2, 0);
cam.update(); // <- However, you must run this line each frame.
Finally, centering the LibGDX app on the device screen should be done outside of Libgdx, otherwise, if you intend to use the spare screen for the same LibGDX app, then you should create another camera to work full screen and render it before the actual game camera, usually used for HUD and such...

libGDX how do you draw on the top left corner of the screen when you are using a viewport and moving the camera

public OrthographicCamera camera;
Viewport viewport;
camera = new OrthographicCamera();
viewport = new ScalingViewport(Scaling.stretch, 1920, 1080, camera);
viewport.apply();
camera.position.set(camera.viewportWidth / 2, camera.viewportHeight / 2, 0);
camera.update();
then I move the camera with my mouse with this code
Vector3 v = new Vector3(Gdx.input.getX(), Gdx.input.getY(), 0);
camera.unproject(v);
camera.position.set(v);
camera.update();
everything works fine except I have some text I want to draw on the top left corner of the screen. I use camera.combined and it draws it on the original screen but it doesn't follow where I move the camera. How do I accomplish this?

Excellent question, I created a method to return a Vector3 which is relative to the screen position. I'm not sure if there is a built in way to do this or easier way but here is my code below. Good luck on your program me.
public Vector3 relativeVector(float x, float y,OrthographicCamera c){
return new Vector3(x+c.position.x-c.viewportWidth/2,y+c.position.y-c.viewportHeight/2,0);
}

LibGDX - Set a background image ( to be static)

I set the background image like this -
batch.draw(Assets.back_sprite, 0, 0, ResX, ResY);
The problem is when i move the camera -
camera.translate(2,0);
The image starting to move backwards and eventually disappears, because I drew it at (0,0)
and the camera is moving in a speed of (2,0), that's why the the image goes away.
The camera is ortho not perspective.
How can i make the image to be static and always stay there?
Any ideas?
Thanks in advance :P

Render it with another camera
OrthographicCamera mStageCamera;
OrthographicCamera mFixedCamera;
SpriteBatch mBatch;
#Override
public void render() {
mBatch.setProjectionMatrix(mFixedCamera.combined);
mBatch.begin();
//render "static" elements
mBatch.end();
mBatch.setProjectionMatrix(mStageCamera.combined);
mBatch.begin();
//render "movable" elements
mBatch.end();
}