Win32: Add glfwAttachWin32Window

Related to #25.

src/win32_platform.h

@@ -272,6 +272,7 @@ typedef struct _GLFWwindowWin32
     GLFWbool            maximized;
     // Whether to enable framebuffer transparency on DWM
     GLFWbool            transparent;
+    GLFWbool            external;
 
     // The last received cursor position, regardless of source
     int                 lastCursorPosX, lastCursorPosY;

src/win32_window.c

@@ -1261,7 +1261,7 @@ void _glfwPlatformDestroyWindow(_GLFWwindow* window)
     if (_glfw.win32.disabledCursorWindow == window)
         _glfw.win32.disabledCursorWindow = NULL;
 
-    if (window->win32.handle)
+    if (window->win32.handle && !window->win32.external)
     {
         RemovePropW(window->win32.handle, L"GLFW");
         DestroyWindow(window->win32.handle);
@@ -1998,3 +1998,102 @@ GLFWAPI HWND glfwGetWin32Window(GLFWwindow* handle)
     return window->win32.handle;
 }
 
+GLFWAPI GLFWwindow* glfwAttachWin32Window(HWND handle, GLFWwindow* share)
+{
+    _GLFWfbconfig fbconfig;
+    _GLFWctxconfig ctxconfig;
+    _GLFWwndconfig wndconfig;
+    _GLFWwindow* window;
+
+    _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
+
+    fbconfig  = _glfw.hints.framebuffer;
+    ctxconfig = _glfw.hints.context;
+    wndconfig = _glfw.hints.window;
+
+    ctxconfig.share = (_GLFWwindow*) share;
+    if (ctxconfig.share)
+    {
+        if (ctxconfig.client == GLFW_NO_API ||
+            ctxconfig.share->context.client == GLFW_NO_API)
+        {
+            _glfwInputError(GLFW_NO_WINDOW_CONTEXT, NULL);
+            return NULL;
+        }
+    }
+
+    if (!_glfwIsValidContextConfig(&ctxconfig))
+        return NULL;
+
+    window = calloc(1, sizeof(_GLFWwindow));
+    window->next = _glfw.windowListHead;
+    _glfw.windowListHead = window;
+
+    window->autoIconify = wndconfig.autoIconify;
+    window->cursorMode  = GLFW_CURSOR_NORMAL;
+
+    window->minwidth    = GLFW_DONT_CARE;
+    window->minheight   = GLFW_DONT_CARE;
+    window->maxwidth    = GLFW_DONT_CARE;
+    window->maxheight   = GLFW_DONT_CARE;
+    window->numer       = GLFW_DONT_CARE;
+    window->denom       = GLFW_DONT_CARE;
+
+    window->win32.handle   = handle;
+    window->win32.external = GLFW_TRUE;
+
+    SetPropW(window->win32.handle, L"GLFW", window);
+    SetWindowLongPtrW(window->win32.handle, GWLP_WNDPROC, (LONG_PTR) windowProc);
+
+    {
+        const DWORD style = GetWindowLongW(window->win32.handle, GWL_STYLE);
+        const DWORD exStyle = GetWindowLongW(window->win32.handle, GWL_EXSTYLE);
+
+        if (style & WS_THICKFRAME)
+            window->resizable = GLFW_TRUE;
+        if (style & (WS_BORDER | WS_THICKFRAME))
+            window->decorated = GLFW_TRUE;
+        if (exStyle & WS_EX_TOPMOST)
+            window->floating = GLFW_TRUE;
+
+        window->win32.maximized = IsZoomed(window->win32.handle);
+        window->win32.iconified = IsIconic(window->win32.handle);
+    }
+
+    if (ctxconfig.client != GLFW_NO_API)
+    {
+        if (ctxconfig.source == GLFW_NATIVE_CONTEXT_API)
+        {
+            if (!_glfwInitWGL())
+                return GLFW_FALSE;
+            if (!_glfwCreateContextWGL(window, &ctxconfig, &fbconfig))
+                return GLFW_FALSE;
+        }
+        else if (ctxconfig.source == GLFW_EGL_CONTEXT_API)
+        {
+            if (!_glfwInitEGL())
+                return GLFW_FALSE;
+            if (!_glfwCreateContextEGL(window, &ctxconfig, &fbconfig))
+                return GLFW_FALSE;
+        }
+        else if (ctxconfig.source == GLFW_OSMESA_CONTEXT_API)
+        {
+            if (!_glfwInitOSMesa())
+                return GLFW_FALSE;
+            if (!_glfwCreateContextOSMesa(window, &ctxconfig, &fbconfig))
+                return GLFW_FALSE;
+        }
+    }
+
+    if (ctxconfig.client != GLFW_NO_API)
+    {
+        if (!_glfwRefreshContextAttribs(window, &ctxconfig))
+        {
+            glfwDestroyWindow((GLFWwindow*) window);
+            return NULL;
+        }
+    }
+
+    return (GLFWwindow*) window;
+}
+