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libGDX camera zoom is different on different devices:

I'm making a game on both desktop and android and the same code results in two different screens (cam.zoom is the same in both):
The desired result is the left screen and the code used to render is like so: (the image is 8000x4000 and is a place holder for my map)
public class MainMenuScreen implements Screen {
private final Application application;
private SpriteBatch batch;
private ShapeRenderer sr;
private OrthographicCamera cam;
private Viewport viewport;
private Button startGame;
private Texture background = new Texture(Gdx.files.internal("background.jpg"));
public MainMenuScreen(final Application application) {
this.application = application;
cam = new OrthographicCamera(WIDTH, HEIGHT);
viewport = new FitViewport(WIDTH, HEIGHT, cam);
batch = this.application.batch;
sr = this.application.sr;
startGame = new Button(-50, -25, 100, 50);
startGame.setColour(new Color(0.01f, 0.35f, 0.47f, 1));
startGame.setText("Start game", this.application.font);
startGame.setHasBorder(true);
startGame.setBorderThickness(3);
startGame.setBorderColour(new Color(0.02f, 0.62f, 0.79f, 1));
startGame.setTextColour(new Color(0.02f, 0.62f, 0.79f, 1));
}
public void update() {
Vector2 mousePos = Extras.getMousePos(viewport);
if (startGame.isClickedOn(mousePos)) {
}
}
#Override
public void render(float delta) {
ScreenUtils.clear(0, 0, 0, 1);
batch.setProjectionMatrix(cam.combined);
sr.setProjectionMatrix(cam.combined);
update();
batch.begin();
batch.draw(background, -background.getWidth() / 2, -background.getHeight() / 2);
batch.end();
startGame.render(this.sr, this.batch);
}
How do I make sure all different devices have the same zoom in the camera?
A possible solution I don't know how to implement yet could be setting cam.zoom to a value dependent on the screen size somehow but there has to be a better way for this using libGDX itself.

First, are you trying to make the button size's same on all device's screen resolution? or you want to make camera zooming have same value?
Ok, How the variable WIDTH and HEIGHT was declared?if you have declared both with one spesific size. Its will be not same if you're trying in another resolutions.
EXAMPLE:
//Constant Spesific Value of WIDTH and HEIGHT Size.
public static final int WIDTH = 1280, HEIGHT = 720;
///////////////////////////////////////////////////
//Non-Constant Value of WIDTH and HEIGHT Size.
public static int WIDTH, HEIGHT;
...
//Define Both In Main.class
public MainGameScreen(){
WIDTH = Gdx.graphics.getWidth();
HEIGHT = Gdx.graphics.getHeight();
}
However, LibGDX's screen resolution can be calculated. Some object size in your game must be spesific, when calculating the size between both WIDTH and HEIGHT you need to know, how the size will be same in all device with one spesific calculation.
EXAMPLE:
/* Button (256x72) in Screen Resolution (1280x720)
Button (160x48) in Screen Resolution (800x480) */
startGame = new Button(0,0, WIDTH/5, HEIGHT/10);
//Button (400x100) in All Screen (Constant Value)
startGame = new Button(0,0, 400, 100);
So, i suggest you to make a calculation to sizing some objects in your game. Because its will be different if you trying to make value in constant.
Ok, the next is, OrthographicCamera Which you want to make same value of zoom right? the cam.zoom is a floating value. Its not a constant value, but it was a variable value that can be changed in all time.
You can trying this code, if you want to zoom camera directly on game
if(Gdx.input.isTouched()){
//Zoom Out
cam.zoom += Gdx.graphics.getDeltaTime();
//Zoom In
cam.zoom -= Gdx.graphics.getDeltaTime();
}
Or if you talking about static-zoom, in a spesific value (not directly changed)
cam.zoom = 1f; //for 1 value of Zoom Out
I hope you understand what i means and im sorry if my answers can't be helpful for you, cause im still learning too, all about LibGDX.

#Alf Equilfe was the one who helped me get to it with his answer and here is the actual solution:
Set WIDTH, HEIGHT to a constant value independent of device size (make it so that any device can handle the size, in my case i chose 1024, 512) and make the aspect ratio the scale so it looks same on all devices.

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.

Add text with grey background to pictures like Snapchat does? Android/Java

Bitmap newBm = ...
Canvas canvas = new Canvas(newBm);
Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setColor(Color.WHITE);
paint.setTextSize((int) (44 * scale));
Rect bounds = new Rect();
paint.getTextBounds(gText, 0, gText.length(), bounds);
canvas.drawText(gText, x, y, paint);
I drew text on the Bitmap like so. How could I get a grey background that is the same height as the text but covers the whole screen??

You could use a Rect. Before drawing the text draw the Rect to the screen:
int screenWidth = getApplicationContext().getResources().getDisplayMetrics().widthPixels;
Rect greyBack = new Rect(0,top,screenWidth,bottom);
Paint paint = new Paint();
paint.setARGB(128, 100, 100, 100); //added alpha because Snapchat has translucent //grey background
canvas.drawRect(greyBack, paint);
top and bottom need to be coordinates above and below the text. You could use y's value and take away a bit for top and add a bit for bottom. How much you add/subtract is up to you and changes the height of the greyBack background.

The best way to see and learn how these sort of things are done with well written code is to look at the android source code itself. For example here is the onDraw method for a TextView it includes additional stuff you won't probably need like compoundPadding, but you can follow it through and get the basic concept of how it's done.

How can i combine orthographic camera X, Y and the input processor screenX, screenY?

I made a two rectangles to divide screen in two regions. Touching in each region do two different things. my camera is like below:
camera = new OrthographicCamera();
camera.setToOrtho(false, 800, 480);
My rectangles are like these:
leftRectangle.set(0, 0, 400, 400);
rightRectangle.set(400, 0, 400, 400);
So what i thought i am doing with camera that, I made my phone screen resolution 800px 400px, whatever my actual resolution, it does not matter, coz i am using camera to do so. But inputprocessor screenX and screenY is returning X,Y according to my phones actual resolution. So I am not getting the camera made touching X,Y. So I am geeting wrong touching value.
How can i make this touching X,Y value same as the camera made resolution?

Use Camera.unproject() to do that.
Vector3 screenCoords = new Vector3(screenX, screenY, 1);
Vector3 cameraCoords = camera.uproject(screenCoords);
float cameraX = cameraCoords.x;
float cameraY = cameraCoords.y;

libgdx and android application. Image as background

I am new and I just start my journey with libgdx. I would like to know how I can do image.png in resolution 960x640 as background in my game? This is possible? Thx for advices and forbearance. Maybe you hava a simply tutorial?
This is my render class:
public void render() {
texture = new Texture(Gdx.files.internal("E:/background.png"));
Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
batch.begin();
batch.draw(texture, 0, 0);
batch.end();
}
Second question. I need to insert two active images, active means when I click on that image, the next image show me on the screen. I want to implement action when I click on that picture.

In your create() method, create a new Texture referencing your image.png, and then use your existing SpriteBatch to render it in the render() loop. Immediately after your GL.clear() call, go your batch.draw(backgroundTexture, 0. 0) and make sure you're in OrthographicProjection mode for your camera.

first you have to set the view port
do this in your create method
`float scrw = 960;
float scrh = 640;
camera = new OrthographicCamera();
camera.viewportHeight = scrh;
camera.viewportWidth = scrw;
camera.position.set(camera.viewportWidth * .5f,
camera.viewportHeight * .5f, 0f);
camera.update();`
create a texture
texture = new Texture("data/background.png");
put this texture in a sprite like this
sprite=new sprite(texture);
and then set the size like this
sprite.setsize(960,640);
and draw it in your render methods between batch.begin
and batch.end
sprite.draw(batch);