modular-vr/Assets/Portal/Runtime/RenderPortals.cs

using System;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Rendering;
using UnityEngine.Rendering.Universal;

namespace EscapeRoomEngine.Portal.Runtime
{
    public class RenderPortals : ScriptableRendererFeature
    {
        private class PortalRenderPass : ScriptableRenderPass
        {
            private RenderStateBlock _renderStateBlock;

            private readonly Settings _settings;

            public PortalRenderPass(Settings settings)
            {
                _settings = settings;
                
                renderPassEvent = RenderPassEvent.AfterRenderingOpaques;
                _renderStateBlock = new RenderStateBlock(RenderStateMask.Nothing);
            }

            public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData)
            {
                var sortingCriteria = renderingData.cameraData.defaultOpaqueSortFlags;
                var drawingSettings =
                    CreateDrawingSettings(
                        new List<ShaderTagId>
                        {
                            new("SRPDefaultUnlit"), new("UniversalForward"), new("UniversalForwardOnly")
                        },
                        ref renderingData, sortingCriteria);

                // set stencil to portal
                var filteringSettings = new FilteringSettings(RenderQueueRange.opaque, _settings.layer);
                drawingSettings.overrideMaterial = _settings.material;
                context.DrawRenderers(renderingData.cullResults, ref drawingSettings, ref filteringSettings, ref _renderStateBlock);
            }
        }

        private PortalRenderPass _portalPass;

        [Serializable]
        public class Settings
        {
            public LayerMask layer;
            public Material material;
        }

        public Settings settings = new();

        public override void Create()
        {
            _portalPass = new PortalRenderPass(settings);
        }

        // Here you can inject one or multiple render passes in the renderer.
        // This method is called when setting up the renderer once per-camera.
        public override void AddRenderPasses(ScriptableRenderer renderer, ref RenderingData renderingData)
        {
            renderer.EnqueuePass(_portalPass);
        }
    }
}