refactor portal rendering into portal camera

Assets/Escape Room Engine/Portal/PortalCamera.cs

@@ -0,0 +1,106 @@
+using System;
+using System.Collections.Generic;
+using UnityEngine;
+using UnityEngine.Rendering;
+using UnityEngine.Rendering.Universal;
+using UnityEngine.XR;
+
+namespace Escape_Room_Engine.Portal
+{
+    [RequireComponent(typeof(Camera))]
+    public class PortalCamera : MonoBehaviour
+    {
+        private static readonly Matrix4x4 HalfRotation = Matrix4x4.Rotate(Quaternion.Euler(0, 180, 0));
+        private static readonly Camera.StereoscopicEye[] Eyes =
+            { Camera.StereoscopicEye.Left, Camera.StereoscopicEye.Right };
+        private static readonly Dictionary<Camera.StereoscopicEye, int> EyeTextureNames = new()
+        {
+            { Camera.StereoscopicEye.Left, Shader.PropertyToID("_LeftTex") },
+            { Camera.StereoscopicEye.Right, Shader.PropertyToID("_RightTex") }
+        };
+
+        /// <summary>
+        /// The minimum near clip plane distance to be used when calculating the oblique clip plane.
+        /// </summary>
+        public float minNearClipPlane = 0.02f;
+        /// <summary>
+        /// The portal this camera renders through.
+        /// </summary>
+        [SerializeField] private Portal portal;
+        /// <summary>
+        /// The quad where the rendered texture will be drawn on.
+        /// </summary>
+        [SerializeField] private MeshRenderer portalQuad;
+
+        private PlayerCamera _playerCamera;
+        private Camera _camera;
+        private readonly Dictionary<Camera.StereoscopicEye, RenderTexture> _textures = new();
+
+        private void Awake()
+        {
+            // get player camera
+            if (Camera.main != null) _playerCamera = Camera.main.GetComponent<PlayerCamera>();
+            else throw new Exception("Main camera has no player camera script set up.");
+            
+            // get portal camera
+            _camera = GetComponent<Camera>();
+        }
+
+        private void OnEnable()
+        {
+            RenderPipelineManager.beginCameraRendering += Render;
+        }
+
+        private void OnDisable()
+        {
+            RenderPipelineManager.beginCameraRendering -= Render;
+        }
+        
+        private void Render(ScriptableRenderContext scriptableRenderContext, Camera camera)
+        {
+            // check whether the portal plane is visible from the player camera
+            var frustumPlanes = GeometryUtility.CalculateFrustumPlanes(_playerCamera.camera);
+            if (!GeometryUtility.TestPlanesAABB(frustumPlanes, portal.other.portalCamera.portalQuad.bounds))
+                // don't render this portal if it is not visible
+                return;
+            
+            var t = portal.transform;
+
+            foreach (var eye in Eyes)
+            {
+                // create portal texture if it doesn't exist yet
+                if (!_textures.ContainsKey(eye))
+                {
+                    if (XRSettings.eyeTextureWidth > 0 && XRSettings.eyeTextureHeight > 0)
+                    {
+                        _textures.Add(eye,
+                            new RenderTexture(XRSettings.eyeTextureWidth, XRSettings.eyeTextureHeight, 24));
+                        portal.other.portalCamera.portalQuad.material.SetTexture(EyeTextureNames[eye], _textures[eye]);
+                    }
+                    else // no texture was created so nothing should be rendered
+                        continue;
+                }
+                
+                // position portal camera
+                var m = t.localToWorldMatrix * HalfRotation * portal.other.transform.worldToLocalMatrix *
+                        _playerCamera.getEyeTransform(eye).localToWorldMatrix;
+                transform.SetPositionAndRotation(m.GetPosition(), m.rotation);
+                _camera.projectionMatrix = _playerCamera.camera.GetStereoProjectionMatrix(eye);
+        
+                // set camera clip plane to portal (otherwise the wall behind the portal would be rendered)
+                // calculating the clip plane: https://computergraphics.stackexchange.com/a/1506
+                var n = -t.forward; // clip plane normal
+                var portalPlane = new Plane(n, t.position); // clip plane in world space
+                var clipPlane = _camera.worldToCameraMatrix.inverse.transpose *
+                                new Vector4(n.x, n.y, n.z, portalPlane.distance); // vector format clip plane in camera space
+                if (Math.Abs(portalPlane.GetDistanceToPoint(transform.position)) >= minNearClipPlane)
+                    // only adjust the near clip plane if it doesn't intersect with the camera
+                    _camera.projectionMatrix = _camera.CalculateObliqueMatrix(clipPlane);
+        
+                // render portal view
+                _camera.targetTexture = _textures[eye];
+                UniversalRenderPipeline.RenderSingleCamera(scriptableRenderContext, _camera);
+            }
+        }
+    }
+}