From 5a82df216dc1a59443eba5fd3655d30ea1d6d724 Mon Sep 17 00:00:00 2001
From: eoineoineoin <helloworld@eoinrul.es>
Date: Sat, 19 Oct 2024 15:13:29 +0100
Subject: [PATCH] Fixes for rendering in multiple windows (#5497)

* Fix race condition when swapping buffers of secondary windows

* Avoid creating opengl 3.3 windows, to avoid Steam overlay bug

* Revert "Avoid creating opengl 3.3 windows, to avoid Steam overlay bug"

This reverts commit 97b5e7f4610d44083215f55d52359942f3363206.

* Add CVar to perform unlocking test
---
 .../Graphics/Clyde/GLContext/GLContextWindow.cs     | 13 +++++++++++--
 Robust.Shared/CVars.cs                              |  8 ++++++++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/Robust.Client/Graphics/Clyde/GLContext/GLContextWindow.cs b/Robust.Client/Graphics/Clyde/GLContext/GLContextWindow.cs
index d5dc1938480..887b954129f 100644
--- a/Robust.Client/Graphics/Clyde/GLContext/GLContextWindow.cs
+++ b/Robust.Client/Graphics/Clyde/GLContext/GLContextWindow.cs
@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Channels;
@@ -176,6 +176,7 @@ private void BlitSecondaryWindows()
                         window.BlitDoneEvent!.Reset();
                         window.BlitStartEvent!.Set();
                         window.BlitDoneEvent.Wait();
+                        window.UnlockBeforeSwap = Clyde._cfg.GetCVar(CVars.DisplayThreadUnlockBeforeSwap);
                     }
                 }
                 else
@@ -212,8 +213,15 @@ private void BlitThreadDoSecondaryWindowBlit(WindowData window)
                 GL.DrawArrays(PrimitiveType.TriangleStrip, 0, 4);
                 Clyde.CheckGlError();
 
-                window.BlitDoneEvent?.Set();
+                if (window.UnlockBeforeSwap)
+                {
+                    window.BlitDoneEvent?.Set();
+                }
                 Clyde._windowing!.WindowSwapBuffers(window.Reg);
+                if (!window.UnlockBeforeSwap)
+                {
+                    window.BlitDoneEvent?.Set();
+                }
             }
 
             private unsafe void BlitThreadInit(WindowData reg)
@@ -336,6 +344,7 @@ private sealed class WindowData
                 public Thread? BlitThread;
                 public ManualResetEventSlim? BlitStartEvent;
                 public ManualResetEventSlim? BlitDoneEvent;
+                public bool UnlockBeforeSwap;
             }
         }
     }
diff --git a/Robust.Shared/CVars.cs b/Robust.Shared/CVars.cs
index c57b3ea6909..d276d0fea89 100644
--- a/Robust.Shared/CVars.cs
+++ b/Robust.Shared/CVars.cs
@@ -1105,6 +1105,14 @@ protected CVars()
         public static readonly CVarDef<bool> DisplayThreadWindowBlit =
             CVarDef.Create("display.thread_window_blit", true, CVar.CLIENTONLY);
 
+        /// <summary>
+        /// Diagnostic flag for testing. When using a separate thread for multi-window blitting,
+        /// should the worker be unblocked before the SwapBuffers(). Setting to true may improve
+        /// performance but may cause crashes or rendering errors.
+        /// </summary>
+        public static readonly CVarDef<bool> DisplayThreadUnlockBeforeSwap =
+            CVarDef.Create("display.thread_unlock_before_swap", false, CVar.CLIENTONLY);
+
         /// <summary>
         /// Buffer size of input command channel from windowing thread to main game thread.
         /// </summary>