From b4a685eba0f91a5a68365c311232b08aeda40605 Mon Sep 17 00:00:00 2001
From: Kleadron <kleadron04@gmail.com>
Date: Tue, 1 Aug 2023 02:36:29 -0700
Subject: [PATCH] Add DWM VSync Code

---
 platforms/windows/main.cpp | 68 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 67 insertions(+), 1 deletion(-)

diff --git a/platforms/windows/main.cpp b/platforms/windows/main.cpp
index 2101f38..cbd96e1 100644
--- a/platforms/windows/main.cpp
+++ b/platforms/windows/main.cpp
@@ -7,7 +7,10 @@
  ********************************************************************/
 
 #include <cstdarg>
+#include <windows.h>
 #include <WindowsX.h>
+//#include <dwmapi.h>
+#include <VersionHelpers.h>
 
 #include "compat/GL.hpp"
 #include "compat/AKeyCodes.hpp"
@@ -19,6 +22,41 @@
 LPCTSTR g_GameTitle = TEXT("MINECRAFT");
 LPCTSTR g_WindowClassName = TEXT("MinecraftClass");
 
+BOOL wantVSync = TRUE;
+
+// windows dwm sync functions
+// On windows versions with the DWM compositor enabled, regular opengl vsync isn't accurate to the compositor's display time.
+// Waiting until DWM has flushed to display a frame results in a smoother experience.
+// If you don't want this, or it causes problems, you can comment out this line.
+// The project does not need to be linked against dwmapi.lib and will find the functions if the DLL exists.
+#define USE_DWM_SYNC
+
+#ifdef USE_DWM_SYNC
+BOOL hasDWM;
+typedef HRESULT(WINAPI *DWMFUNC1)(BOOL *pfEnabled);
+typedef HRESULT(WINAPI *DWMFUNC2)();
+DWMFUNC1 p_DwmIsCompositionEnabled;
+DWMFUNC2 p_DwmFlush;
+
+void linkDWM()
+{
+	HMODULE dwmapiLib = LoadLibrary("dwmapi.dll");
+
+	if (dwmapiLib != NULL)
+	{
+		printf("Found dwmapi.dll, vsync will sync to compositor.");
+		p_DwmIsCompositionEnabled = (DWMFUNC1)GetProcAddress(dwmapiLib, "DwmIsCompositionEnabled");
+		p_DwmFlush = (DWMFUNC2)GetProcAddress(dwmapiLib, "DwmFlush");
+		hasDWM = true;
+	}
+	else
+	{
+		printf("No dwmapi.dll, vsync will sync to monitor.");
+		hasDWM = false;
+	}
+}
+#endif
+
 void LogMsg(const char* fmt, ...)
 {
 	va_list lst;
@@ -191,6 +229,10 @@ int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPTSTR lpCmdLin
 
 	g_AppPlatform.initConsts();
 
+#ifdef USE_DWM_SYNC
+	linkDWM();
+#endif
+
 	// register the window class:
 	WNDCLASS wc;
 	wc.style = CS_OWNDC;
@@ -230,7 +272,6 @@ int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPTSTR lpCmdLin
 	if (!xglInitted())
 		goto _cleanup;
 
-	xglSwapIntervalEXT(1);
 
 	g_pApp = new NinecraftApp;
 	g_pApp->m_pPlatform = &g_AppPlatform;
@@ -259,6 +300,31 @@ int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPTSTR lpCmdLin
 			// update our stuff here:
 			g_pApp->update();
 
+			if (wantVSync)
+			{
+				// todo: check if DWM sync is appropriate for versions over 7/vista
+#ifdef USE_DWM_SYNC
+				if (hasDWM && IsWindowsVistaOrGreater())
+				{
+					BOOL enabled = FALSE;
+
+					if (SUCCEEDED(p_DwmIsCompositionEnabled(&enabled)) && enabled)
+					{
+						xglSwapIntervalEXT(0);
+						p_DwmFlush();
+					}
+				}
+				else
+#endif
+				{
+					xglSwapIntervalEXT(1);
+				}
+			}
+			else
+			{
+				xglSwapIntervalEXT(0);
+			}
+
 			// note: NinecraftApp would have done this with eglSwapBuffers, but I'd rather do it here:
 			SwapBuffers(hDC);
 		}