add transparent window support for Windows Vista and up

examples/gears.c

@@ -314,6 +314,7 @@ int main(int argc, char *argv[])
     glfwWindowHint(GLFW_DEPTH_BITS, 16);
     glfwWindowHint(GLFW_ALPHA_BITS, 8);
     glfwWindowHint(GLFW_TRANSPARENT, GLFW_TRUE);
+    glfwWindowHint(GLFW_DECORATED, GLFW_FALSE);
 
     window = glfwCreateWindow( 300, 300, "Gears", NULL, NULL );
     if (!window)

src/win32_init.c

@@ -97,6 +97,8 @@ static GLFWbool loadLibraries(void)
             GetProcAddress(_glfw.win32.dwmapi.instance, "DwmIsCompositionEnabled");
         _glfw.win32.dwmapi.DwmFlush = (DWMFLUSH_T)
             GetProcAddress(_glfw.win32.dwmapi.instance, "DwmFlush");
+        _glfw.win32.dwmapi.DwmEnableBlurBehindWindow = (DWMENABLEBLURBEHINDWINDOW_T)
+            GetProcAddress(_glfw.win32.dwmapi.instance, "DwmEnableBlurBehindWindow");
     }
 
     _glfw.win32.shcore.instance = LoadLibraryA("shcore.dll");

src/win32_platform.h

@@ -120,21 +120,32 @@ typedef enum PROCESS_DPI_AWARENESS
 } PROCESS_DPI_AWARENESS;
 #endif /*DPI_ENUMS_DECLARED*/
 
+typedef struct _DWM_BLURBEHIND
+{
+    DWORD dwFlags;
+    BOOL fEnable;
+    HRGN hRgnBlur;
+    BOOL fTransitionOnMaximized;
+} DWM_BLURBEHIND, *PDWM_BLURBEHIND;
+
 // winmm.dll function pointer typedefs
 typedef MMRESULT (WINAPI * JOYGETDEVCAPS_T)(UINT,LPJOYCAPS,UINT);
 typedef MMRESULT (WINAPI * JOYGETPOS_T)(UINT,LPJOYINFO);
 typedef MMRESULT (WINAPI * JOYGETPOSEX_T)(UINT,LPJOYINFOEX);
 typedef DWORD (WINAPI * TIMEGETTIME_T)(void);
+typedef HRESULT(WINAPI * DWMENABLEBLURBEHINDWINDOW_T)(HWND, const DWM_BLURBEHIND*);
 #define _glfw_joyGetDevCaps _glfw.win32.winmm.joyGetDevCaps
 #define _glfw_joyGetPos _glfw.win32.winmm.joyGetPos
 #define _glfw_joyGetPosEx _glfw.win32.winmm.joyGetPosEx
 #define _glfw_timeGetTime _glfw.win32.winmm.timeGetTime
+#define _glfw_DwmEnableBlurBehindWindow _glfw.win32.dwmapi.DwmEnableBlurBehindWindow
 
 // user32.dll function pointer typedefs
 typedef BOOL (WINAPI * SETPROCESSDPIAWARE_T)(void);
 typedef BOOL (WINAPI * CHANGEWINDOWMESSAGEFILTEREX_T)(HWND,UINT,DWORD,PCHANGEFILTERSTRUCT);
 #define _glfw_SetProcessDPIAware _glfw.win32.user32.SetProcessDPIAware
 #define _glfw_ChangeWindowMessageFilterEx _glfw.win32.user32.ChangeWindowMessageFilterEx
+#define _glfw_DwmEnableBlurBehindWindow _glfw.win32.dwmapi.DwmEnableBlurBehindWindow
 
 // dwmapi.dll function pointer typedefs
 typedef HRESULT (WINAPI * DWMISCOMPOSITIONENABLED_T)(BOOL*);
@@ -237,6 +248,7 @@ typedef struct _GLFWlibraryWin32
         HINSTANCE       instance;
         DWMISCOMPOSITIONENABLED_T DwmIsCompositionEnabled;
         DWMFLUSH_T      DwmFlush;
+        DWMENABLEBLURBEHINDWINDOW_T DwmEnableBlurBehindWindow;
     } dwmapi;
 
     // shcore.dll

src/win32_window.c

@@ -732,6 +732,19 @@ static int createWindow(_GLFWwindow* window, const _GLFWwndconfig* wndconfig)
     window->win32.numer     = GLFW_DONT_CARE;
     window->win32.denom     = GLFW_DONT_CARE;
 
+    // Accelerated transparent windows
+    // It currently doesn't support decorated windows.
+    // If decorated is required we just return an opaque window.
+    // Since DwmEnableBlurBehindWindow is supported since Vista,
+    // previous versions will simply get an opaque window.
+    if (!window->decorated && _glfw_DwmEnableBlurBehindWindow && window->transparent) {
+        DWM_BLURBEHIND bb = { 0 };
+        bb.dwFlags = 3; // DWM_BB_ENABLE | DWM_BB_BLURREGION
+        bb.hRgnBlur = CreateRectRgn(0, 0, -1, -1); // an invalid hRgnBlur makes the the window transparent
+        bb.fEnable = TRUE;
+        _glfw_DwmEnableBlurBehindWindow(window->win32.handle, &bb);
+    }
+
     return GLFW_TRUE;
 }