OpticsSimulation.Unity/Assets/Scenes/RaycastMath.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using static OpticalSurface2D;

public class RaycastMath
{
    public struct RaycastResult2D {
        public Vector2 Point;
        public Vector2 Normal;
    }

    public static bool RaycastCircle(Ray2D ray, float radius, ref RaycastResult2D result) {
        var vToCircleCenter = Vector2.zero - ray.origin;

        bool isInsideCircle = vToCircleCenter.magnitude < radius;

        var d = Vector2.Dot(vToCircleCenter, ray.direction.normalized);


        if(d < 0 && ray.origin.magnitude > radius) {
            return false;
        }

        var p = ray.origin + ray.direction.normalized * d;

        var v = Vector2.zero - p;

        var rayCenterDistance = v.magnitude;
        if (rayCenterDistance > radius) {
            return false;
        } else if (rayCenterDistance == radius) {
            result.Point = p;
            result.Normal = p.normalized;
        } else {

            float m = Mathf.Sqrt(radius * radius - rayCenterDistance * rayCenterDistance);

            if (isInsideCircle) {
                result.Point = p + ray.direction.normalized * m;
                result.Normal = result.Point.normalized;
            } else {
                result.Point = p - ray.direction.normalized * m;
                result.Normal = result.Point.normalized;
            }
        }
        return true;
    }


    public static bool RayLineIntersection(Vector2 rayOrigin, Vector2 rayDirection, Vector2 lineOrigin, Vector2 lineDirection, ref Vector2 hitPoint) {
        Vector2 rayTangent = new Vector2(-rayDirection.y, rayDirection.x);

        float distanceToLine = Vector2.Dot(lineOrigin - rayOrigin, rayTangent);
        float origin2ExtensionDistance = distanceToLine / Vector2.Dot(-rayTangent, lineDirection);
        hitPoint = origin2ExtensionDistance * lineDirection + lineOrigin;

        return Vector2.Dot(hitPoint - rayOrigin, rayDirection) > 0.0f;
    }

    public static bool RayLineSegmentIntersection(Vector2 rayOrigin, Vector2 rayDirection, Vector2 lineOrigin, Vector2 lineP2, ref Vector2 hitPoint) {
        Vector2 rayTangent = new Vector2(-rayDirection.y, rayDirection.x);

        Vector2 lineDirection = lineP2 - lineOrigin;


        float distanceToLine = Vector2.Dot(lineOrigin - rayOrigin, rayTangent);
        float origin2ExtensionDistance = distanceToLine / Vector2.Dot(-rayTangent, lineDirection);
        hitPoint = origin2ExtensionDistance * lineDirection + lineOrigin;

        if (Vector2.Dot(hitPoint - rayOrigin, rayDirection) < 0.0f) {
            return false;
        }

        var d = Vector2.Dot(hitPoint - lineOrigin, lineDirection.normalized);
        if (d < 0.0f || d > lineDirection.magnitude) {
            return false;
        }

        return true;
    }
}