无需抬起手指即可检测滑动手势

Question

I am developing a game for android with libgdx and I have a little problem, I want to make it trigger a function when the user swipes, this I achieve. The problem is that it runs the function when you finish swiping (when you lift your finger). How can I make the function run while the swipe is doing?

This is the current code for the gesture listener:

private static class DirectionGestureListener extends GestureAdapter{

    DirectionListener directionListener;

    public DirectionGestureListener(DirectionListener directionListener){
        this.directionListener = directionListener;
    }

    @Override
    public boolean fling(float velocityX, float velocityY, int button) {
        if(Math.abs(velocityX)>Math.abs(velocityY)){
            if(velocityX>0){
                directionListener.onRight();
            }else{
                directionListener.onLeft();
            }
        }else{
            if(velocityY>0){
                directionListener.onDown();
            }else{
                directionListener.onUp();
            }
        }
        return super.fling(velocityX, velocityY, button);
    }

}

And the game scene:

Gdx.input.setInputProcessor(new SimpleDirectionGestureDetector(new SimpleDirectionGestureDetector.DirectionListener() {
    @Override
    public void onUp() { 
        /*something*/ 
    }

    @Override
    public void onRight() { 
        /*something*/ 
    }

    @Override
    public void onLeft() { 
        /*something*/ 
    }

    @Override
    public void onDown() { 
        /*something*/
    }
}));

Answer 1

I looked into GestureDetector.java of libgdx source code itself. fling() will be executed whenever event of touchUp() happened. Thus aligned with what you experienced.

I think an option to make this work is to implement such gesture detection yourself by extending InputAdapter class or implementing InputProcessor interface class, then work on touchDown() , and touchDragged() to have an intended effect as you aimed for.

The idea is to keep track of touch id as it firstly touched on the screen inside touchDown() (its 3rd parameter is int button which is what you're looking at), then use that id to check and further operate inside touchDragged() . If id matches, then for simple approach, you can check whether user touched and moved for pre-defined distance by comparing it against original touching position.

Let's say we want a swipe gesture only when user firstly touches the screen, moves it for (at least) distance we pre-defined set, and within pre-defined duration. So if user firstly touches the screen, moves finger around but still not more than pre-defined distance, then finally moves far enough within duration we've set, this still won't be treated as swipe as our conditions set that it must be from first intention (first touch) to do such gesture. This means we calculate distance against original touching point, not moved point. Of course, you can customize the conditions to suit your need too.

From above, conditions to regard it as swipe gesture can include following (you can adapt these yourself)

• distance it moved compared to original touching point
• duration it took to move (might be 150ms, etc), longer duration user can be more relaxing not to act fast to make it registered as swipe gesture
• only 1 swipe at a time can be taken into effect ie if user uses 2 fingers (2 touches) to swipe at the same time, only first one (or last one) can be used as swipe effect, etc.

Treating it separately for x, y direction is per your need. If so, you have to add handling code inside touchDragged() to check for both direction and send you corresponding event ie swipe-x, or swipe-y per se. Then you hook it up by calling one of your method to let your game knows.