Angry Birds, Silver: Looping Legend code for Unity3D

SilverLooper.cs

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

// kurtdekker
// A looping downward attack like Angry Birds, Silver: Looping Legend
//
// To use:
//	- put this on your Rigidbody2D object
//	- send it flying
//	- set Trigger property true to initiate loop
//
// NOTE: this works for both left/right travel, but it is up to you
// to choose graphics that look correct traveling to the left.
//
// See full package at: https://forum.unity.com/threads/silver-like-movement.1251579
//

public class SilverLooper : MonoBehaviour
{
	[Header( "Input: set this true to start (or call Trigger())")]
	public bool Trigger;

	[Header( "Radius of the loop.")]
	public float CircleRadius = 1.0f;

	[Header( "Optionally match entry to downward attack.")]
	public bool MatchEntryToDownwardAttack;

	// means we are started in the loop
	bool initiated;
	// means we have completed the loop
	bool finishedLooping;

	float originalSpeed;

	float positionOnCircle;
	float finalPositionOnCircle;
	float rotationalRate;

	float distanceBeforeTurning;

	Rigidbody2D rb2d;

	void Start()
	{
		rb2d = GetComponent<Rigidbody2D>();
	}

	public void TriggerLoop()
	{
		Trigger = true;
	}

	void Update()
	{
		if (!initiated)
		{
			if (Trigger)
			{
				initiated = true;

				// observe our velocity now
				Vector3 originalVelocity = rb2d.velocity;

				// compute our initial speed
				originalSpeed = originalVelocity.magnitude;

				// We need to turn angles fast enough to do 360 degrees
				// in the circumference distance of 2 * pi * radius
				rotationalRate = (originalSpeed * 360) / (Mathf.PI * 2 * CircleRadius);

				// this is just for clockwise vs counter clockwise
				if (originalVelocity.x < 0)
				{
					rotationalRate *= -1;
				}

				// find out what part of an imaginary circle we would
				// be on while traveling at this angle.
				float radians = Mathf.Atan2( -originalVelocity.x, originalVelocity.y);

				// this will track our pointing as we go around
				positionOnCircle = radians * Mathf.Rad2Deg;

				// we're gonna be going down for final attack
				finalPositionOnCircle = -180;

				// make sure we get to our final position
				if (rotationalRate > 0)
				{
					while( finalPositionOnCircle < positionOnCircle)
					{
						finalPositionOnCircle += 360;
					}
				}
				if (rotationalRate < 0)
				{
					while( finalPositionOnCircle > positionOnCircle)
					{
						finalPositionOnCircle += 360;
					}
				}

				// turn off gravity... we'll take it from here
				rb2d.gravityScale = 0.0f;

				distanceBeforeTurning = 0.0f;

				// OPTIONAL: help the player by continuing straight ahead briefly
				// in order to roughly match our target down-stroke attack point
				// on the loop
				if (MatchEntryToDownwardAttack)
				{
					float xVelocity = originalVelocity.x;
					float yVelocity = originalVelocity.y;

					// Only adjust it up to a certain slope
					// Beyond this limit slope, we cap out
					const float LimitSlope = 2.0f;
					if (Mathf.Abs( yVelocity) > LimitSlope * Mathf.Abs( xVelocity))
					{
						yVelocity = Mathf.Abs( xVelocity) * Mathf.Sign( yVelocity) * LimitSlope;
					}

					float angle = Mathf.Atan( yVelocity / xVelocity);

					float sine = Mathf.Sin( angle);

					distanceBeforeTurning = Mathf.Abs( 1 + sine) * CircleRadius;
				}

				// show where we were in space when we tripped the loop
				VisibleMarkerObject.Create( rb2d.position);
			}
		}
	}

	void FixedUpdate ()
	{
		if (initiated)
		{
			if (!finishedLooping)
			{
				if (distanceBeforeTurning > 0)
				{
					distanceBeforeTurning -= originalSpeed * Time.deltaTime;
				}
				else
				{
					positionOnCircle += rotationalRate * Time.deltaTime;

					if (rotationalRate > 0)
					{
						if (positionOnCircle > finalPositionOnCircle)
						{
							positionOnCircle = finalPositionOnCircle;
							finishedLooping = true;
						}
					}
					if (rotationalRate < 0)
					{
						if (positionOnCircle < finalPositionOnCircle)
						{
							positionOnCircle = finalPositionOnCircle;
							finishedLooping = true;
						}
					}
				}
			}

			Vector3 velocity = Quaternion.Euler( 0, 0, positionOnCircle) * Vector3.up;

			velocity *= originalSpeed;

			rb2d.velocity = velocity;
		}
	}
}