Detecting swipe from Unity3D c# scripts

Let me share a simple code to detect swipe from Unity 3D application. The sample code is written in c#, but it can easily be ported to other languages.

Please find the code below, I guess the code is documented enough to understand.

This implementation detects swipe using angle of swipe from X and Y axis.


using UnityEngine;
using System.Collections;

public class SwipeDetector : MonoBehaviour {

    private const int mMessageWidth  = 200;
    private const int mMessageHeight = 64;

    private readonly Vector2 mXAxis = new Vector2(1, 0);
    private readonly Vector2 mYAxis = new Vector2(0, 1);

    private readonly string [] mMessage = {
        "",
        "Swipe Left",
        "Swipe Right",
        "Swipe Top",
        "Swipe Bottom"
    };

    private int mMessageIndex = 0;

    // The angle range for detecting swipe
    private const float mAngleRange = 30;

    // To recognize as swipe user should at lease swipe for this many pixels
    private const float mMinSwipeDist = 50.0f;

    // To recognize as a swipe the velocity of the swipe
    // should be at least mMinVelocity
    // Reduce or increase to control the swipe speed
    private const float mMinVelocity  = 2000.0f;

    private Vector2 mStartPosition;
    private float mSwipeStartTime;

    // Use this for initialization
    void Start () {
    }
    
    // Update is called once per frame
    void Update () {

        // Mouse button down, possible chance for a swipe
        if (Input.GetMouseButtonDown(0)) {
            // Record start time and position
            mStartPosition = new Vector2(Input.mousePosition.x,
                                         Input.mousePosition.y);
            mSwipeStartTime = Time.time;
        }

        // Mouse button up, possible chance for a swipe
        if (Input.GetMouseButtonUp(0)) {
            float deltaTime = Time.time - mSwipeStartTime;

            Vector2 endPosition  = new Vector2(Input.mousePosition.x,
                                               Input.mousePosition.y);
            Vector2 swipeVector = endPosition - mStartPosition;

            float velocity = swipeVector.magnitude/deltaTime;

            if (velocity > mMinVelocity &&
                swipeVector.magnitude > mMinSwipeDist) {
                // if the swipe has enough velocity and enough distance

                swipeVector.Normalize();

                float angleOfSwipe = Vector2.Dot(swipeVector, mXAxis);
                angleOfSwipe = Mathf.Acos(angleOfSwipe) * Mathf.Rad2Deg;

                // Detect left and right swipe
                if (angleOfSwipe < mAngleRange) {
                    OnSwipeRight();
                } else if ((180.0f - angleOfSwipe) < mAngleRange) {
                    OnSwipeLeft();
                } else {
                    // Detect top and bottom swipe
                    angleOfSwipe = Vector2.Dot(swipeVector, mYAxis);
                    angleOfSwipe = Mathf.Acos(angleOfSwipe) * Mathf.Rad2Deg;
                    if (angleOfSwipe < mAngleRange) {
                        OnSwipeTop();
                    } else if ((180.0f - angleOfSwipe) < mAngleRange) {
                        OnSwipeBottom();
                    } else {
                        mMessageIndex = 0;
                    }
                }
            }
        }
    }

    void OnGUI() {
        // Display the appropriate message
        GUI.Label(new Rect((Screen.width-mMessageWidth)/2,
                           (Screen.height-mMessageHeight)/2,
                            mMessageWidth, mMessageHeight),
                  mMessage[mMessageIndex]);
    }

    private void OnSwipeLeft() {
        mMessageIndex = 1;
    }

    private void OnSwipeRight() {
        mMessageIndex = 2;
    }

    private void OnSwipeTop() {
        mMessageIndex = 3;
    }

    private void OnSwipeBottom() {
        mMessageIndex = 4;
    }
}