Use DwmFlush when DWM is enabled.

Use DwmFlush instead of WGL_EXT_swap_control when desktop compositing is
enabled, to avoid the jitter of DWM and WGL vsync fighting.

Fixes #516.

src/glfw_config.h.in

@@ -57,8 +57,6 @@
 // Define this to 1 if building as a shared library / dynamic library / DLL
 #cmakedefine _GLFW_BUILD_DLL
 
-// Define this to 1 if glfwSwapInterval should ignore DWM compositing status
-#cmakedefine _GLFW_USE_DWM_SWAP_INTERVAL
 // Define this to 1 to force use of high-performance GPU on Optimus systems
 #cmakedefine _GLFW_USE_OPTIMUS_HPG
 

src/wgl_context.c

@@ -570,6 +570,14 @@ void _glfwPlatformMakeContextCurrent(_GLFWwindow* window)
 
 void _glfwPlatformSwapBuffers(_GLFWwindow* window)
 {
+    // HACK: Use DwmFlush when desktop composition is enabled
+    if (_glfwIsCompositionEnabled())
+    {
+        int count = window->wgl.interval;
+        while (count--)
+            _glfw_DwmFlush();
+    }
+
     SwapBuffers(window->wgl.dc);
 }
 
@@ -577,12 +585,12 @@ void _glfwPlatformSwapInterval(int interval)
 {
     _GLFWwindow* window = _glfwPlatformGetCurrentContext();
 
-#if !defined(_GLFW_USE_DWM_SWAP_INTERVAL)
-    // HACK: Don't enabled vsync when desktop compositing is enabled, as it
-    //       leads to severe frame jitter on some cards
-    if (_glfwIsCompositionEnabled() && interval)
-        return;
-#endif
+    window->wgl.interval = interval;
+
+    // HACK: Disable WGL swap interval when desktop composition is enabled to
+    //       avoid interfering with DWM vsync
+    if (_glfwIsCompositionEnabled())
+        interval = 0;
 
     if (window->wgl.EXT_swap_control)
         window->wgl.SwapIntervalEXT(interval);

src/wgl_context.h

@@ -44,6 +44,7 @@ typedef struct _GLFWcontextWGL
 {
     HDC       dc;              // Private GDI device context
     HGLRC     context;         // Permanent rendering context
+    int       interval;
 
     // WGL extensions (context specific)
     PFNWGLSWAPINTERVALEXTPROC           SwapIntervalEXT;

src/win32_init.c

@@ -96,6 +96,8 @@ static GLboolean initLibraries(void)
     {
         _glfw.win32.dwmapi.DwmIsCompositionEnabled = (DWMISCOMPOSITIONENABLED_T)
             GetProcAddress(_glfw.win32.dwmapi.instance, "DwmIsCompositionEnabled");
+        _glfw.win32.dwmapi.DwmFlush = (DWMFLUSH_T)
+            GetProcAddress(_glfw.win32.dwmapi.instance, "DwmFlush");
     }
 
     return GL_TRUE;

src/win32_platform.h

@@ -121,7 +121,9 @@ typedef BOOL (WINAPI * CHANGEWINDOWMESSAGEFILTEREX_T)(HWND,UINT,DWORD,PCHANGEFIL
 
 // dwmapi.dll function pointer typedefs
 typedef HRESULT (WINAPI * DWMISCOMPOSITIONENABLED_T)(BOOL*);
+typedef HRESULT (WINAPI * DWMFLUSH_T)(VOID);
 #define _glfw_DwmIsCompositionEnabled _glfw.win32.dwmapi.DwmIsCompositionEnabled
+#define _glfw_DwmFlush _glfw.win32.dwmapi.DwmFlush
 
 
 #define _GLFW_RECREATION_NOT_NEEDED 0
@@ -195,6 +197,7 @@ typedef struct _GLFWlibraryWin32
     struct {
         HINSTANCE       instance;
         DWMISCOMPOSITIONENABLED_T DwmIsCompositionEnabled;
+        DWMFLUSH_T      DwmFlush;
     } dwmapi;
 
 } _GLFWlibraryWin32;

src/win32_window.c

@@ -565,15 +565,12 @@ static LRESULT CALLBACK windowProc(HWND hWnd, UINT uMsg,
 
         case WM_DWMCOMPOSITIONCHANGED:
         {
-            if (_glfwIsCompositionEnabled())
-            {
-                _GLFWwindow* previous = _glfwPlatformGetCurrentContext();
-                _glfwPlatformMakeContextCurrent(window);
-                _glfwPlatformSwapInterval(0);
-                _glfwPlatformMakeContextCurrent(previous);
-            }
-
-            // TODO: Restore vsync if compositing was disabled
+            // HACK: Re-apply interval when desktop composition is toggled to
+            //       ensure WGL swap interval is disabled when necessary
+            _GLFWwindow* previous = _glfwPlatformGetCurrentContext();
+            _glfwPlatformMakeContextCurrent(window);
+            _glfwPlatformSwapInterval(window->wgl.interval);
+            _glfwPlatformMakeContextCurrent(previous);
             break;
         }