Near clipping plane calculation

    // Check original author!!!
    // https://github.com/SebLague/Portals/blob/master/Assets/Scripts/Core/Portal.cs
    void SetNearClipPlane () {
        // Learning resource:
        // http://www.terathon.com/lengyel/Lengyel-Oblique.pdf
        Transform clipPlane = transform;
        int dot = System.Math.Sign (Vector3.Dot (clipPlane.forward, transform.position - portalCam.transform.position));

        Vector3 camSpacePos = portalCam.worldToCameraMatrix.MultiplyPoint (clipPlane.position);
        Vector3 camSpaceNormal = portalCam.worldToCameraMatrix.MultiplyVector (clipPlane.forward) * dot;
        float camSpaceDst = -Vector3.Dot (camSpacePos, camSpaceNormal) + nearClipOffset;

        // Don't use oblique clip plane if very close to portal as it seems this can cause some visual artifacts
        if (Mathf.Abs (camSpaceDst) > nearClipLimit) {
            Vector4 clipPlaneCameraSpace = new Vector4 (camSpaceNormal.x, camSpaceNormal.y, camSpaceNormal.z, camSpaceDst);

            // Update projection based on new clip plane
            // Calculate matrix with player cam so that player camera settings (fov, etc) are used
            portalCam.projectionMatrix = playerCam.CalculateObliqueMatrix (clipPlaneCameraSpace);
        } else {
            portalCam.projectionMatrix = playerCam.projectionMatrix;
        }
    }