Joe Greubel edited this page Jun 15, 2018 · 5 revisions

Polling refers to checking the current state of an input device, e.g. is a specific key pressed, where is the first finger on the screen and so on. It's a quick and easy way to process user input and will suffice for most arcade games.

Caution: If you rely on polling, you might miss events, e.g. a fast paced key down/key up. If you need to make sure a specific sequence of input action was completed, use event handling instead.

Polling the Keyboard

Polling for input from a Keyboard is done with just one simple line of code, like below.

boolean isAPressed = Gdx.input.isKeyPressed(Keys.A);

The parameter passed to that method is a Key Code. Rather than having to memorize these codes there is a static class within the Input interface that contains the codes which you can use. They can be seen here.

Polling the Touch Screen / Mouse

There are a number of methods concerning polling the touch screen/mouse. To check whether one or more fingers are currently on the screen (which is equivalent to a mouse button being pressed) you can do the following:

boolean isTouched = Gdx.input.isTouched();

For multi-touch input you might be interested whether a specific finger (pointer) is currently on the screen:

// Will Return whether the screen is currently touched
boolean firstFingerTouching = Gdx.input.isTouched(0);
boolean secondFingerTouching = Gdx.input.isTouched(1);
boolean thirdFingerTouching = Gdx.input.isTouched(2);

Each finger that goes down on the screen gets a so called pointer index. The first finger to go down gets the index 0, the next one gets the index 1 and so on. If a finger is lifted off the screen and touched down again, while other fingers are still on the screen, the finger will get the first free index. An example:

  1. first finger goes down -> 0
  2. second finger goes down -> 1
  3. third finger goes down -> 2
  4. second finger goes up -> 1 becomes free
  5. first finger goes up -> 0 becomes free, at this point only 2 is used
  6. another finger goes down -> 0, as it is the first free index

On the desktop or the browser you will only ever have a single "finger" so to speak.

If you want to check if the user touched down and released any finger again you can use the following method:

// Will return whether the screen has just been touched
boolean justTouched = Gdx.input.justTouched();

This can be used in situations where you want to check a touch down/up sequence really quickly, e.g. on a screen that says "touch screen to continue". Note that it is not a reliable method as it is based on polling.

To get the coordinates of a specific finger you can use the following methods:

int firstX = Gdx.input.getX();
int firstY = Gdx.input.getY();
int secondX = Gdx.input.getX(1);
int secondY = Gdx.input.getY(1);

Here we get the touch coordinates at pointer index 0 (0 is default) and pointer index 1. Coordinates are reported in a coordinate system relative to the screen. The origin (0, 0) is in the upper left corner of the screen, the x-axis points to the right, the y-axis points downwards.

Mouse Buttons

On the desktop you can also check which mouse buttons are currently pressed:

boolean leftPressed = Gdx.input.isButtonPressed(Input.Buttons.LEFT);
boolean rightPressed = Gdx.input.isButtonPressed(Input.Buttons.RIGHT);

See the Buttons class for more constants.

Note that on Android we only emulate the left mouse button. Any touch event will be interpreted as if it was issued with a left mouse button press. Touch screens obviously don't have a notion of left, right and middle button.

Prev | Next

Table of Contents

Clone this wiki locally
You can’t perform that action at this time.
You signed in with another tab or window. Reload to refresh your session. You signed out in another tab or window. Reload to refresh your session.
Press h to open a hovercard with more details.