Scroller.cs

using System;
using System.Collections.Generic;
using UnityEngine;

public class Scroller
{
	public float maxDragSpeed = 20.0f; //maximum drag speed
	public float edgeSquish = 60.0f; //how far to go past the end
	public float edgeBounce = 0.19f; //how much force to use to bounce back
	public float strongFriction = 0.75f; //used to bring it to a stop quicker
	public float weakFriction = 0.87f; //used when throwing at high speed
	public float slowSpeed = 3.0f; //below this speed it will be brought to a stop quickly
	
	private bool _isDragging = false;

	public Scroller()
	{
	}

	public void StartDrag()
	{
		if(_isDragging) return;

		_isDragging = true;
	}

	public void EndDrag()
	{
		if(!_isDragging) return;

		_isDragging = false;
	}

	public bool CalculateScrollUpdate(ref float pos, ref float speed, float boundsMin, float boundsMax)
	{
		float diff = 0;

		if(pos < boundsMin)
		{
			diff = boundsMin - pos;
		}
		else if(pos > boundsMax)
		{
			diff = boundsMax - pos;
		}

		if(_isDragging) //restrict the speed based on how far it's out of bounds
		{
			float diffEased = Mathf.Abs(diff) / edgeSquish;
			speed *= Mathf.Max(0.0f,1.0f - Mathf.Sqrt(diffEased));
			speed = Mathf.Clamp(speed,-maxDragSpeed,maxDragSpeed);
		}
		else //bring it back in from the edge with squish speed
		{

			if(Mathf.Abs(speed) > 0.01f || Mathf.Abs(diff) > 1.0f)
			{
				if(Mathf.Abs(diff) > 0.0f || Mathf.Abs(speed) < slowSpeed) //slow it down if it's out of bounds OR close to stopping
				{
					speed *= strongFriction;
				}
				else
				{
					speed *= weakFriction;
				}
			}
			else //it's done moving, stahp!
			{
				speed = 0.0f;

				//put it at the exact edge
				if(pos < boundsMin)
				{
					pos = boundsMin;
				}
				else if(pos > boundsMax)
				{
					pos = boundsMax;
				}

				return false; //it's not moving anymore!
			}

			pos += speed + diff * edgeBounce;
		}

		return true; //it's still moving
	}

	public void CalculateScrollDrag(ref float pos, ref float speed, float boundsMin, float boundsMax)
	{
		float diff = 0;

		if(pos < boundsMin)
		{
			diff = boundsMin - pos;
		}
		else if(pos > boundsMax)
		{
			diff = boundsMax - pos;
		}

		if(diff == 0) //it's in bounds, move normally
		{
			pos += speed;
		}
		else //out of bounds the movement gets spongey!
		{
			float diffEased = Mathf.Abs(diff) / edgeSquish;
			pos += speed * Mathf.Max(0.0f,1.0f - Mathf.Sqrt(diffEased)); //note how we don't modify speed itself
		}
	}
}