touchDragged如何在libgdx中工作？

Question

我目前正在学习libgdx游戏编程，现在我已经学会了如何使用touchDown但是我不知道如何使用touchDragged。计算机如何知道手指被拖动的方向（用户是向左还是向右拖动）

Answer 1

The computer doesn't know that. Or at least the interface won't tell you this information. It looks like this:

public boolean touchDragged(int screenX, int screenY, int pointer);

It is nearly the same like touchDown:

public boolean touchDown(int screenX, int screenY, int pointer, int button);

After a touchDown event happened, only touchDragged events will occur (for the same pointer) until a touchUp event gets fired. If you want to know the direction in which the pointer moved, you have to calculate it yourself by computing the delta (difference) between the last touchpoint and the current one. That might look like this:

private Vector2 lastTouch = new Vector2();

public boolean touchDown(int screenX, int screenY, int pointer, int button) {
    lastTouch.set(screenX, screenY);
}

public boolean touchDragged(int screenX, int screenY, int pointer) {
    Vector2 newTouch = new Vector2(screenX, screenY);
    // delta will now hold the difference between the last and the current touch positions
    // delta.x > 0 means the touch moved to the right, delta.x < 0 means a move to the left
    Vector2 delta = newTouch.cpy().sub(lastTouch);
    lastTouch = newTouch;
}

Answer 2

The touch dragged method is called every frame that the touch position changes. The touch down method is called every time you touch the screen down, and touch up when you release.

LibGDX - Get Swipe Up or swipe right etc.?

This can help you a little bit.