beyond/Assets/Scripts/PortalCamera.cs

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


namespace Beyond
{

    [RequireComponent(typeof(Camera))]
    [ExecuteAlways]
    public class PortalCamera : MonoBehaviour
    {
        public GameObject target;
        Camera mCam;
        public Vector3 xVec = new Vector3(1, 0, 0);
        public Vector3 yVec = new Vector3(0, 1, 0);
        public Vector3 zVec = new Vector3(0, 0, -1);
        MeshFilter mMesh;
        Bounds bounds;
        Vector4[] quadPoints = new Vector4[4];
        Vector4[] camSpaceQuadPoints = new Vector4[4];
        // Start is called before the first frame update
        void Start()
        {
            mCam = GetComponent<Camera>();
            CalculateQuadPoints();
        }

        public float CalculateFOV()
        {
            float correction = 1f;
            /*
            if (targetQuad)
            {
                mCam.transform.LookAt(targetQuad.transform);
                Vector3 forward = transform.InverseTransformDirection(targetQuad.transform.forward);
                correction = -forward.x / forward.z;
            }
            */
            float zPlaneDist = 0f;
            zPlaneDist = Vector3.Dot(-target.transform.forward, transform.position);
            float fov = Mathf.Atan2(target.transform.localScale.x / correction, zPlaneDist) * Mathf.Rad2Deg * 2.0f;
            float fov2 = Mathf.Atan2(target.transform.localScale.x, -transform.localPosition.z) * Mathf.Rad2Deg;
            Debug.Log("FOV: " + fov);
            return fov;
        }


        static public Matrix4x4 CalculateOffcenterProjectionMatrix(float near, float far, float left, float right, float top, float bottom)
        {
            Matrix4x4 m = Matrix4x4.identity;
            float x = 2.0F * near / (right - left);
            float y = 2.0F * near / (top - bottom);
            float a = (right + left) / (right - left);
            float b = (top + bottom) / (top - bottom);
            float c = -(far + near) / (far - near);
            float d = -(2.0F * far * near) / (far - near);
            float e = -1.0F;
            m[0, 0] = x;
            m[0, 1] = 0;
            m[0, 2] = a;
            m[0, 3] = 0;
            m[1, 0] = 0;
            m[1, 1] = y;
            m[1, 2] = b;
            m[1, 3] = 0;
            m[2, 0] = 0;
            m[2, 1] = 0;
            m[2, 2] = c;
            m[2, 3] = d;
            m[3, 0] = 0;
            m[3, 1] = 0;
            m[3, 2] = e;
            m[3, 3] = 0;
            return m;

        }

        static public Matrix4x4 CalculateProjectionMatrix(float near, float far, float aspect, float fov)
        {
            Matrix4x4 m = Matrix4x4.identity;
            float left, right, top, bottom;
            float scale = Mathf.Tan(fov * 0.5f * Mathf.Deg2Rad) * near;
            right = aspect * scale;
            left = -right;
            top = scale;
            bottom = -top;

            float x = 2.0F * near / (right - left);
            float y = 2.0F * near / (top - bottom);
            float a = (right + left) / (right - left);
            float b = (top + bottom) / (top - bottom);
            float c = -(far + near) / (far - near);
            float d = -(2.0F * far * near) / (far - near);
            float e = -1.0F;
            m[0, 0] = x;
            m[0, 1] = 0;
            m[0, 2] = a;
            m[0, 3] = 0;
            m[1, 0] = 0;
            m[1, 1] = y;
            m[1, 2] = b;
            m[1, 3] = 0;
            m[2, 0] = 0;
            m[2, 1] = 0;
            m[2, 2] = c;
            m[2, 3] = d;
            m[3, 0] = 0;
            m[3, 1] = 0;
            m[3, 2] = e;
            m[3, 3] = 0;
            return m;

        }
        // Update is called once per frame
        void Update()
        {

        }

        void CalculateQuadPoints()
        {
            Vector3 pos = target.transform.TransformPoint(bounds.center);
            Vector3 right = target.transform.right * bounds.extents.x;
            Vector3 up = target.transform.up * bounds.extents.y;
            quadPoints[0] = pos + right + up;
            quadPoints[1] = pos - right + up;
            quadPoints[2] = pos - right - up;
            quadPoints[3] = pos + right - up;

            for (int i = 0; i < 4; i++)
                quadPoints[i].w = 1;
        }

        void CalculateCamSpacePoints()
        {
            for (int i = 0; i < 4; i++)
            {
                camSpaceQuadPoints[i] = mCam.worldToCameraMatrix * quadPoints[i];
                camSpaceQuadPoints[i] /= camSpaceQuadPoints[i].w;
            }
        }

        private void OnDrawGizmosSelected()
        {

            mCam = GetComponent<Camera>();
            //Gizmos.DrawCube()
            Vector4[] cubePoints = new Vector4[8];
            Matrix4x4 mat = (mCam.projectionMatrix * mCam.worldToCameraMatrix).inverse;
            for (int i = 0; i < 8; i++)
            {
                cubePoints[i] = new Vector4(i % 2 == 0 ? -1f : 1f, (i / 2) % 2 == 0 ? -1f : 1f, (i / 4) % 2 == 0 ? -1f : 1f, 1f);
                cubePoints[i] = mat * cubePoints[i];
                cubePoints[i] /= cubePoints[i].w;
            }
            Gizmos.color = Color.red;
            Gizmos.DrawLine(cubePoints[0], cubePoints[1]);
            Gizmos.DrawLine(cubePoints[2], cubePoints[3]);
            Gizmos.DrawLine(cubePoints[0], cubePoints[2]);
            Gizmos.DrawLine(cubePoints[1], cubePoints[3]);

            Gizmos.DrawLine(cubePoints[4], cubePoints[5]);
            Gizmos.DrawLine(cubePoints[6], cubePoints[7]);
            Gizmos.DrawLine(cubePoints[4], cubePoints[6]);
            Gizmos.DrawLine(cubePoints[5], cubePoints[7]);

            Gizmos.DrawLine(cubePoints[0], cubePoints[4]);
            Gizmos.DrawLine(cubePoints[1], cubePoints[5]);
            Gizmos.DrawLine(cubePoints[2], cubePoints[6]);
            Gizmos.DrawLine(cubePoints[3], cubePoints[7]);

            CalculateQuadPoints();

            CalculateCamSpacePoints();

            for (int i = 0; i < 4; i++)
                Gizmos.DrawLine(camSpaceQuadPoints[i], camSpaceQuadPoints[(i + 1) % 4]);

           
           // for (int i = 0; i < 4; i++)
             //   Gizmos.DrawLine(camSpaceQuadPoints[i], camSpaceQuadPoints[(i + 1) % 4]);

            //Gizmos.DrawLine(cubePoints[3], cubePoints[0]);
        }
        // Update is called once per frame
        void LateUpdate()
        {
            if (!target)
                return;

          
            if (!mMesh)
            {
                mMesh = target.GetComponent<MeshFilter>();
                bounds = mMesh.mesh.bounds;
            }
            transform.up = Vector3.Cross(transform.right, transform.forward);
            transform.forward = target.transform.forward;
            transform.right = target.transform.right;


            Vector3 forward = transform.InverseTransformDirection(target.transform.forward);
            xVec.z = -forward.x / forward.z;
            yVec.z = -forward.y / forward.z;

            Matrix4x4 skewMat = Matrix4x4.identity;
            skewMat.SetColumn(0, xVec);
            skewMat.SetColumn(1, yVec);
            skewMat.SetColumn(2, zVec);

            mCam.worldToCameraMatrix = skewMat * transform.worldToLocalMatrix;
            CalculateQuadPoints();

            CalculateCamSpacePoints();

            mCam.projectionMatrix = CalculateOffcenterProjectionMatrix(-camSpaceQuadPoints[0].z, 1000f, camSpaceQuadPoints[1].x, camSpaceQuadPoints[0].x, camSpaceQuadPoints[0].y, camSpaceQuadPoints[2].y);

        }
    }
}