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I'm trying to create a football game where the user will make a flick gesture in order to kick the ball. I'm quite new to developing games in unity3d, I have successfully made a moving ball, added some rotation, gravity and some basic input (the ball follows the touch coordinates). How can I achieve the flick gesture?

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If you want to stay in the "Unity state of mind" and keep your code platform independent (even if just so you can easily test on your desktop), I found the easiest way to handle gestures is using one of the gesture plugins.

I can recommend two:

  1. TouchKit by Prime31 - free and open source
  2. Input.Touches - available in the asset store, not free.

Also worth mentioning is TouchScript a very professional free library, but may be an overkill for your needs.

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At my company we use FingerGestures

Using that add-on, you'd be listening for and responding to events like: FingerGestures.OnFingerDragBegin += FingerGestures_OnFingerDragBegin; FingerGestures.OnFingerDragMove += FingerGestures_OnFingerDragMove; FingerGestures.OnFingerDragEnd += FingerGestures_OnFingerDragEnd;

Use the position returned from drag begin and drag end to determine the magnitude and direction of the drag, and record the start and end times in the event handlers to see how fast the gesture was. A drag done quickly is a flick.

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A nice resource regarding basics of flick gesturing at MSDN

Regarding Unity3D, you can take help from the following resource

The following code may help you

    // one finger gestures
    if (iPhoneInput.touchCount == 1) {

        // finger data
        iPhoneTouch f0 = iPhoneInput.GetTouch(0);

        // finger delta
        Vector3 f0Delta = new Vector3(f0.deltaPosition.x, -f0.deltaPosition.y, 0);

        // if finger moving
        if (f0.phase == iPhoneTouchPhase.Moved) {

            // compute orbit speed
            orbitSpeed += (f0Delta + f0Delta * distWeight) * orbitScreenToWorldRatio * Time.deltaTime;

    // two fingers gestures
    else if (iPhoneInput.touchCount == 2) {

        // fingers data
        iPhoneTouch f0 = iPhoneInput.GetTouch(0);
        iPhoneTouch f1 = iPhoneInput.GetTouch(1);

        // fingers positions
        Vector3 f0Pos = new Vector3(f0.position.x, f0.position.y, 0);
        Vector3 f1Pos = new Vector3(f1.position.x, f1.position.y, 0);

        // fingers movements
        Vector3 f0Delta = new Vector3(f0.deltaPosition.x, f0.deltaPosition.y, 0);
        Vector3 f1Delta = new Vector3(f1.deltaPosition.x, f1.deltaPosition.y, 0);

        // fingers distance
        float f0f1Dist = Vector3.Distance(f0.position, f1.position);

        // if both fingers moving
        if (f0.phase == iPhoneTouchPhase.Moved && f1.phase == iPhoneTouchPhase.Moved) {

            // fingers moving direction
            Vector3 f0Dir = f0Delta.normalized;
            Vector3 f1Dir = f1Delta.normalized;

            // dot product of directions
            float dot = Vector3.Dot(f0Dir, f1Dir);

            // if fingers moving in opposite directions
            if (dot < -0.7f) {

                float pinchDelta = f0f1Dist - lastf0f1Dist;

                // if fingers move more than a threshold
                if (Mathf.Abs(pinchDelta) > 2) {

                    // if pinch out, zoom in 
                    if (f0f1Dist > lastf0f1Dist && zoomDistance > zoomNearLimit) {
                        zoomSpeed += (pinchDelta + pinchDelta * distWeight) * Time.deltaTime * zoomScreenToWorldRatio;

                    // if pinch in, zoom out
                    else if (f0f1Dist < lastf0f1Dist && zoomDistance < zoomFarLimit) {
                        zoomSpeed += (pinchDelta + pinchDelta * distWeight) * Time.deltaTime * zoomScreenToWorldRatio;

                // detect twist
                if (f0Delta.magnitude > 2 && f1Delta.magnitude > 2) {

                    // homemade algorithm works, but needs code review
                    Vector3 fingersDir = (f1Pos - f0Pos).normalized;
                    Vector3 twistNormal = Vector3.Cross(fingersDir, Vector3.forward);
                    Vector3 twistAxis = Vector3.Cross(fingersDir, twistNormal);
                    float averageDelta = (f0Delta.magnitude + f1Delta.magnitude) / 2;
                    if (Vector3.Dot(f0Dir, twistNormal) > 0.7f) {
                        twistSpeed =  twistAxis.z * averageDelta * Time.deltaTime * twistScreenToWorldRatio;
                    else if (Vector3.Dot(f0Dir, twistNormal) < -0.7f) {
                        twistSpeed = -twistAxis.z * averageDelta * Time.deltaTime * twistScreenToWorldRatio;

        // record last distance, for delta distances
        lastf0f1Dist = f0f1Dist;

        // decelerate zoom speed
        zoomSpeed = zoomSpeed * (1 - Time.deltaTime * 10);
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