DualSlider.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.Events;
using UnityEngine.EventSystems;
using UnityEngine.Serialization;

namespace UI
{
    [System.Serializable]
    public class OnDualSliderValuesChanged : UnityEvent<float, float>
    {
    }


    public class DualSlider : MonoBehaviour, IPointerHoverHandler, IPointerDownHandler, IPointerUpHandler
    {
        public Sprite SliderSprite;
        public Color SliderColor = new Color32 (101, 131, 161, 220);
        public OnDualSliderValuesChanged OnValuesChanged;

        private GameObject leftSlider;
        private GameObject rightSlider;

        private bool slidingLeft = false;
        private bool slidingRight = false;

        float curLeft = 0f;
        float curRight = 0f;

        // Use this for initialization
        void Start () {
            leftSlider = new GameObject ("LeftSlider");
            Image leftSliderImg = leftSlider.AddComponent<Image> ();
            leftSliderImg.sprite = SliderSprite;
            leftSliderImg.material = GetComponent<Image> ().material;
            leftSliderImg.color = SliderColor;
            leftSlider.transform.SetParent (transform, false);
            RectTransform lRect = leftSlider.GetComponent<RectTransform> ();
            lRect.anchorMin = new Vector2 (0, 0);
            lRect.anchorMax = new Vector2 (1, 1);
            lRect.offsetMin = new Vector2( 0, 0 );
            lRect.offsetMax = new Vector2( 0, 0 );

            rightSlider = new GameObject ("RightSlider");
            Image rightSliderImg = rightSlider.AddComponent<Image> ();
            rightSliderImg.sprite = SliderSprite;
            rightSliderImg.material = GetComponent<Image> ().material;
            rightSliderImg.color = SliderColor;
            rightSlider.transform.SetParent (transform, false);
            RectTransform rRight = rightSlider.GetComponent<RectTransform> ();
            rRight.anchorMin = new Vector2 (0, 0);
            rRight.anchorMax = new Vector2 (1, 1);
            rRight.offsetMin = new Vector2( 0, 0 );
            rRight.offsetMax = new Vector2( 0, 0 );

            setValues (0.01f, 0.99f);
        }

        public void setValues( float left, float right )
        {
            left = Mathf.Clamp (left, 0f, 1f);
            right = Mathf.Clamp (right, 0f, 1f);
            RectTransform rect = GetComponent<RectTransform> ();
            leftSlider.GetComponent<RectTransform>().offsetMax = new Vector2( -rect.rect.width*(1f-left), 0 );
            rightSlider.GetComponent<RectTransform>().offsetMin = new Vector2( rect.rect.width*right, 0 );

            curLeft = left;
            curRight = right;
            // Activate the callback
            if( OnValuesChanged != null )
                OnValuesChanged.Invoke (curLeft, curRight);
        }

        public void OnPointerDown( PointerEventData data )
        {
            slidingLeft = false;
            slidingRight = false;

            Vector2 localMousePos;
            RectTransform rectTf = GetComponent<RectTransform> ();
            if (RectTransformUtility.ScreenPointToLocalPointInRectangle (rectTf, data.position, data.enterEventCamera, out localMousePos)) {
                Rect r = rectTf.rect;

                float amount = (localMousePos.x + r.size.x * 0.5f) / r.size.x;

                float distToLeftSlider = Mathf.Abs (amount - curLeft);
                float distToRightSlider = Mathf.Abs (amount - curRight);
                if (distToLeftSlider < distToRightSlider) {
                    slidingLeft = true;
                } else {
                    slidingRight = true;
                }
            }
        }

        public void OnPointerUp( PointerEventData data )
        {
            slidingLeft = false;
            slidingRight = false;
        }

        public void OnPointerHover( PointerEventData data )
        {
            if( InputDeviceManager.instance.currentInputDevice.isLeftButtonDown() && (slidingLeft || slidingRight )) {
                Vector2 localMousePos;
                RectTransform rectTf = GetComponent<RectTransform> ();
                if (RectTransformUtility.ScreenPointToLocalPointInRectangle (rectTf, data.position, data.enterEventCamera, out localMousePos)) {
                    Rect r = rectTf.rect;

                    float amount = (localMousePos.x + r.size.x * 0.5f) / r.size.x;
                    if (slidingLeft) {
                        float right = curRight;
                        if (amount > right)
                            right = amount;
                        setValues (amount, right);
                    } else if (slidingRight) {
                        float left = curLeft;
                        if (amount < left)
                            left = amount;
                        setValues (left, amount);
                    }
                }
            }
        }
    }
}