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.

CMakeLists.txt

@@ -26,7 +26,6 @@ option(GLFW_INSTALL "Generate installation target" ON)
 option(GLFW_DOCUMENT_INTERNALS "Include internals in documentation" OFF)
 
 if (WIN32)
-    option(GLFW_USE_DWM_SWAP_INTERVAL "Set swap interval even when DWM compositing is enabled" OFF)
     option(GLFW_USE_OPTIMUS_HPG "Force use of high-performance GPU on Optimus systems" OFF)
 endif()
 
@@ -236,9 +235,6 @@ if (_GLFW_WIN32)
 
     list(APPEND glfw_PKG_LIBS "-lgdi32")
 
-    if (GLFW_USE_DWM_SWAP_INTERVAL)
-        set(_GLFW_USE_DWM_SWAP_INTERVAL 1)
-    endif()
     if (GLFW_USE_OPTIMUS_HPG)
         set(_GLFW_USE_OPTIMUS_HPG 1)
     endif()

README.md

@@ -65,6 +65,8 @@ GLFW bundles a number of dependencies in the `deps/` directory.
  - Minimum required CMake version updated to 2.8.12
  - Bugfix: Initialization failed on headless systems
  - Bugfix: The cached current context could get out of sync
+ - [Win32] Removed `GLFW_USE_DWM_SWAP_INTERVAL` compile-time option
+ - [Win32] Bugfix: Swap interval was ignored when DWM was enabled
  - [Cocoa] Bugfix: The cached `NSScreen` for a monitor could get out of sync
  - [Cocoa] Bugfix: The `GLFW_AUTO_ICONIFY` window hint was ignored
  - [Cocoa] Bugfix: Resizing a window to its minimum size would segfault

docs/compile.dox

@@ -221,11 +221,6 @@ DLL version of the Visual C++ library is used.  It is recommended to set this to
 `ON`, as this keeps the executable smaller and benefits from security and bug
 fix updates of the Visual C++ runtime.
 
-`GLFW_USE_DWM_SWAP_INTERVAL` determines whether the swap interval is set even
-when DWM compositing is enabled.  If this is `ON`, the swap interval is set even
-if DWM is enabled.  It is recommended to set this to `OFF`, as doing otherwise
-can lead to severe jitter.
-
 `GLFW_USE_OPTIMUS_HPG` determines whether to export the `NvOptimusEnablement`
 symbol, which forces the use of the high-performance GPU on Nvidia Optimus
 systems.  This symbol needs to be exported by the EXE to be detected by the

docs/window.dox

@@ -825,8 +825,6 @@ interval of one lets you avoid tearing.
 
 Note that this may not work on all machines, as some drivers have
 user-controlled settings that override any swap interval the application
-requests.  It is also by default disabled on Windows Vista and later when using
-DWM (Aero), as using it there sometimes leads to severe jitter.  You can
-forcibly enable it for machines using DWM using @ref compile_options_win32.
+requests.
 
 */

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;
         }