Parallax background script (by codemonkey)

ParallaxBackground.cs

using UnityEngine;

public class ParallaxBackground : MonoBehaviour {

    [SerializeField] private Vector2 parallaxEffectMultiplier;
    [SerializeField] private bool infiniteHorizontal;
    [SerializeField] private bool infiniteVertical;

    private Transform cameraTransform;
    private Vector3 lastCameraPosition;
    private float spriteWidth;
    private float spriteHeight;
    
    private void Start() {
        cameraTransform = Camera.main.transform;
        lastCameraPosition = cameraTransform.position;
        Sprite sprite = GetComponent<SpriteRenderer>().sprite;
        Texture2D texture = sprite.texture;
        spriteWidth = texture.width / sprite.pixelsPerUnit;
        spriteHeight = texture.height / sprite.pixelsPerUnit;
    }

    private void LateUpdate() {
        MoveBackgroundRelativeToCamera();

        if (infiniteHorizontal)
        {
            if (CameraPassedEdgeOfSpriteX) {
                float howFarToMoveCameraX = DistanceBetweenMiddleOfCameraAndMiddleOfBackgroundX % spriteWidth;
                transform.position = new Vector3(cameraTransform.position.x + howFarToMoveCameraX, transform.position.y);
            }
        }

        if (infiniteVertical) {
            if (CameraPassedEdgeOfSpriteY) {
                float howFarToMoveCameraY = DistanceBetweenMiddleOfCameraAndMiddleOfBackgroundY % spriteHeight;
                transform.position = new Vector3(transform.position.x, cameraTransform.position.y + howFarToMoveCameraY);
            }
        }
    }

    private void MoveBackgroundRelativeToCamera()
    {
        Vector3 currentCameraPosition = cameraTransform.position;
        Vector3 amountCameraMovedSinceLastFrame = currentCameraPosition - lastCameraPosition;
        transform.position += new Vector3(amountCameraMovedSinceLastFrame.x * parallaxEffectMultiplier.x, amountCameraMovedSinceLastFrame.y * parallaxEffectMultiplier.y);
        lastCameraPosition = currentCameraPosition;
    }
    
    
    // Code cleanup.
    private float DistanceBetweenMiddleOfCameraAndMiddleOfBackgroundX => cameraTransform.position.x - transform.position.x;
    private float DistanceBetweenMiddleOfCameraAndMiddleOfBackgroundY => cameraTransform.position.y - transform.position.y;

    private bool CameraPassedEdgeOfSpriteX =>
        (Mathf.Abs(DistanceBetweenMiddleOfCameraAndMiddleOfBackgroundX) >= spriteWidth);
    private bool CameraPassedEdgeOfSpriteY =>
        (Mathf.Abs(DistanceBetweenMiddleOfCameraAndMiddleOfBackgroundY) >= spriteHeight);
}