From 1c80e99008923f126853fe633e26d9d8ccefa13a Mon Sep 17 00:00:00 2001
From: Camilla Berglund <elmindreda@elmindreda.org>
Date: Sun, 7 Jul 2013 23:29:13 +0200
Subject: [PATCH] Added forcing of swap interval on DWM composition.

---
 CMakeLists.txt    | 8 ++++++++
 README.md         | 6 ++++++
 src/config.h.in   | 2 ++
 src/wgl_context.c | 2 ++
 4 files changed, 18 insertions(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5a5ea841..13d51d25 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -16,6 +16,10 @@ option(GLFW_BUILD_TESTS "Build the GLFW test programs" ON)
 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)
+endif()
+
 if (APPLE)
     option(GLFW_BUILD_UNIVERSAL "Build GLFW as a Universal Binary" OFF)
     option(GLFW_USE_CHDIR "Make glfwInit chdir to Contents/Resources" ON)
@@ -151,6 +155,10 @@ if (_GLFW_WIN32)
         set(_GLFW_NO_DLOAD_WINMM 1)
         list(APPEND glfw_LIBRARIES winmm)
     endif()
+
+    if (GLFW_USE_DWM_SWAP_INTERVAL)
+        set(_GLFW_USE_DWM_SWAP_INTERVAL 1)
+    endif()
 endif()
 
 #--------------------------------------------------------------------
diff --git a/README.md b/README.md
index f3446ebb..c0171a67 100644
--- a/README.md
+++ b/README.md
@@ -72,6 +72,10 @@ directory of bundled applications to the `Contents/Resources` directory.
 `USE_MSVC_RUNTIME_LIBRARY_DLL` determines whether to use the DLL version or the
 static library version of the Visual C++ runtime library.
 
+`GLFW_USE_DWM_SWAP_INTERVAL` determines whether the swap interval is set even
+when DWM compositing is enabled.  This can lead to severe jitter and is not
+usually recommended.
+
 
 #### EGL specific options
 
@@ -101,6 +105,8 @@ See the [GLFW 3.0 documentation](http://www.glfw.org/docs/3.0/).
 
  - Bugfix: The `-Wall` flag was not used with Clang and other GCC compatibles
  - Bugfix: The default for `GLFW_ALPHA_BITS` was set to zero
+ - [Win32] Added `_GLFW_USE_DWM_SWAP_INTERVAL` for forcing the swap interval
+           to be set even when DWM compositing is enabled
  - [Win32] Bugfix: The clipboard string was not freed on terminate
  - [Win32] Bugfix: Entry points for OpenGL 1.0 and 1.1 functions were not
                    returned by `glfwGetProcAddress`
diff --git a/src/config.h.in b/src/config.h.in
index 4e60ccf0..22b9f695 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -56,6 +56,8 @@
 
 // Define this to 1 to disable dynamic loading of winmm
 #cmakedefine _GLFW_NO_DLOAD_WINMM
+// Define this to 1 if glfwSwapInterval should ignore DWM compositing status
+#cmakedefine _GLFW_USE_DWM_SWAP_INTERVAL
 
 // Define this to 1 if glXGetProcAddress is available
 #cmakedefine _GLFW_HAS_GLXGETPROCADDRESS
diff --git a/src/wgl_context.c b/src/wgl_context.c
index 4c009124..7bac477c 100644
--- a/src/wgl_context.c
+++ b/src/wgl_context.c
@@ -600,12 +600,14 @@ void _glfwPlatformSwapInterval(int interval)
 {
     _GLFWwindow* window = _glfwPlatformGetCurrentContext();
 
+#if !defined(_GLFW_USE_DWM_SWAP_INTERVAL)
     if (_glfwIsCompositionEnabled())
     {
         // Don't enabled vsync when desktop compositing is enabled, as it leads
         // to frame jitter
         return;
     }
+#endif
 
     if (window->wgl.EXT_swap_control)
         window->wgl.SwapIntervalEXT(interval);