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

// This class manages the rendering effects of portals.

// !!! Caution: Modifying this code without proper understanding may lead to unintended consequences. !!!

public class WorkingPortal : MonoBehaviour {

    // The portal that this portal is linked to; the one whose view is seen when looking through this portal.
    public WorkingPortal linkedWorkingPortal;

    // The mesh renderer that renders the portal.
    public MeshRenderer screen;

    // Determines if the portal is visible from the camera.
    public bool visibleFromCamera = true;

    public GameObject myGameObject;

    // The render texture that this portal's camera renders to, providing the view when looking through the linked portal.
    public RenderTexture viewTexture;

    // The camera used for rendering this portal.
    public Camera WorkingPortalCam;

    // Offset values for adjusting the near clipping plane.
    float nearClipOffset = 0.05f;
    float nearClipLimit = 0.2f;

    // Reference to the player's camera.
    Camera playerCam;

    // Mesh filter of the portal's screen.
    MeshFilter screenMeshFilter;

    void Awake () {
        // Set reference to this GameObject.
        myGameObject = gameObject;

        // Disable camera rendering by default; rendering is triggered manually via the Render() function.
        WorkingPortalCam.enabled = false;

        // Retrieve the mesh filter component of the portal screen.
        screenMeshFilter = screen.GetComponent<MeshFilter> ();

        // Set the display mask to render solid color instead of the camera view.
        screen.material.SetInt ("displayMask", 1);
    }

    // Renders the view through this portal.
    public void Render (Camera newplayerCam) {
        if (!visibleFromCamera) {
            return;
        }
        playerCam = newplayerCam;

        CreateViewTexture ();

        // This section aligns the portal camera with the player's view and renders only the portion visible through the portal.

        var localToWorldMatrix = playerCam.transform.localToWorldMatrix;
        var renderPosition = new Vector3();
        var renderRotation = new Quaternion();

        WorkingPortalCam.projectionMatrix = playerCam.projectionMatrix;
        localToWorldMatrix = transform.localToWorldMatrix * linkedWorkingPortal.transform.worldToLocalMatrix * localToWorldMatrix;
        renderPosition = localToWorldMatrix.GetColumn (3);
        renderRotation = localToWorldMatrix.rotation;

        // Hide the portal screen to allow camera to see through it.
        screen.shadowCastingMode = UnityEngine.Rendering.ShadowCastingMode.ShadowsOnly;
        linkedWorkingPortal.screen.material.SetInt ("displayMask", 1);

        WorkingPortalCam.transform.SetPositionAndRotation (renderPosition, renderRotation);
        SetNearClipPlane ();
        WorkingPortalCam.Render ();

        // Revert hiding objects that were hidden at the start of rendering.
        screen.shadowCastingMode = UnityEngine.Rendering.ShadowCastingMode.On;
    }

    void CreateViewTexture () {
        if (viewTexture == null || viewTexture.width != Screen.width || viewTexture.height != Screen.height) {
            if (viewTexture != null) {
                viewTexture.Release ();
            }
            viewTexture = new RenderTexture (Screen.width, Screen.height, 0);
            // Render the view from the portal camera to the view texture.
            WorkingPortalCam.targetTexture = viewTexture;
            // Display the view texture on the screen of the linked portal.
            linkedWorkingPortal.screen.material.SetTexture ("_MainTex", viewTexture);
        }
    }

    // Adjusts the near clipping plane to align with the surface of the portal.
    void SetNearClipPlane () {
        Transform clipPlane = transform;
        int dot = System.Math.Sign (Vector3.Dot (clipPlane.forward, transform.position - WorkingPortalCam.transform.position));

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

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

            // Update projection based on the new clip plane.
            // Calculate matrix with player cam to use its settings (e.g., fov).
            WorkingPortalCam.projectionMatrix = playerCam.CalculateObliqueMatrix (clipPlaneCameraSpace);
        } else {
            // Use default projection matrix if very close to the portal.
            WorkingPortalCam.projectionMatrix = playerCam.projectionMatrix;
        }
    }
}