Using unProject correctly in Java Libgdx

Question

I want to make a button clickable, but it isn't working - it seems like I need to use unproject() but I can't figure out how. The code in question is:

Texture playButtonImage;
SpriteBatch batch;
ClickListener clickListener;
Rectangle playButtonRectangle;
Vector2 touchPos;
OrthographicCamera camera;

@Override
public void show() {
    playButtonImage = new Texture(Gdx.files.internal("PlayButton.png"));

    camera = new OrthographicCamera();
    camera.setToOrtho(false, 800, 480);
    batch = new SpriteBatch();

    playButtonRectangle = new Rectangle();
    playButtonRectangle.x = 400;
    playButtonRectangle.y = 250;
    playButtonRectangle.width = 128;
    playButtonRectangle.height = 64;
}

@Override
public void render(float delta) {
    Gdx.gl.glClearColor(0, 0, 0.2f, 1);
    Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);

    camera.update();
    batch.setProjectionMatrix(camera.combined);

    batch.begin();
    batch.draw(playButtonImage, playButtonRectangle.x, playButtonRectangle.y);
    batch.end();

    if (Gdx.input.isTouched()) {
        Vector2 touchPos = new Vector2();
        touchPos.set(Gdx.input.getX(), Gdx.input.getY());


        if (playButtonRectangle.contains(touchPos)) {
            batch.begin();
            batch.draw(playButtonImage, 1, 1);
            batch.end();
        }
    }
}

It's possible that the screen coordinate (0,0) is in the top left, but the camera has coordinate (0,0) in the bottom left. What happens if you use Gdx.input.getY()*-1? — Ryan, Sep 01 '13 at 00:57

score 13 · Accepted Answer · answered Sep 01 '13 at 05:57

In general you use camera.unproject(Vector) to transform your screen coordinates from a click or touch to your gameworld. This is needed because the origin is not necessarily the same and using the camera you can also zoom in and out, move around, rotate and so on. Unprojecting will take care of all of that and give you your game world coordinate matching the pointers position.

In your example it would go like this:

Vector3 touchPos = new Vector3(Gdx.input.getX(), Gdx.input.getY(), 0);
camera.unproject(touchPos);

Having this said you should actually not do this UI task manually. Libgdx has also some shipped UI functionality which is called a Stage (see this). There are lots of widgets already available (see this). They use skins (you can get a basic one from here, you need all the uiskin.* files). They automatically forward inputevents to the socalled Actors, e.g. a button, and you just need to implement handling of those events.

As stated in my answer initializing a new Vector3 object on every frame when touched is introducing a lot of overhead. GC cycles are heavy especially on time critical applications like games (even worse on mobile; and libgdx is built for mobile too) — laubed, Mar 29 '15 at 20:55
You can also use Pools to get around the problem of initializing a new Vector3. — bazola, Apr 05 '17 at 19:43

score 4 · Answer 2 · answered Mar 27 '15 at 20:26

with camera.unproject(Vector3); you can translate screen coordinates to game world coordinates.

Vector3 tmpCoords = new Vector3(Gdx.input.getX(), Gdx.input.getY(), 0);
camera.unproject(tmpCoords);

tmpCoords.x //is now the touched X coordinate in the game world coordinate system
tmpCoords.y //is now the touched Y coordinate in the game world coordinate system.

In addition to that it is best practice to define a tmpVector as a field an Instantiate a Vector3 object only once. You can then do the same with the .set() method.

tmpCoords.set(Gdx.input.getX(), Gdx.input.getY(), 0);
camera.unproject(tmpCoords);

tmpCoords.x //is now the touched X coordinate in the game world coordinate system
tmpCoords.y //is now the touched Y coordinate in the game world coordinate system.

Therefore you reduce object creation and remove unnecessary GC calls which lead to microlag.

score 1 · Answer 3 · answered Sep 01 '13 at 09:23

@Override
public void render(float delta) {
Gdx.gl.glClearColor(0, 0, 0.2f, 1);
Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);

camera.update();
batch.setProjectionMatrix(camera.combined);

batch.begin();
batch.draw(playButtonImage, playButtonRectangle.x, playButtonRectangle.y);
batch.end();

if (Gdx.input.isTouched()) {
    Vector3 touchPos = new Vector3();
    touchPos.set(Gdx.input.getX(), Gdx.input.getY(),0);
    camera.unproject(touchPos);


    if (playButtonRectangle.contains(touchPos.x, touchPos.y)) {
        batch.begin();
        batch.draw(playButtonImage, 1, 1);
        batch.end();
    }
   }
   }

score 0 · Answer 4 · answered Sep 01 '13 at 09:18

0

when ever u need a touch point from user and to convert those touchpoints to camera u need to unproject them to camera coordinates by camera coordinates

camera.unproject(touchPos.set(Gdx.input.getX(), Gdx.input.getY(), 0));

answered Sep 01 '13 at 09:18

Kumar Saurabh

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Using unProject correctly in Java Libgdx

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