Win32: Fix maximization showing a hidden window

The normal way of maximizing a window also makes it visible.  This
implements window maximization manually for when the window passed to
glfwMaximizeWindow is hidden.

This will very likely not be forward-compatible and should be replaced.

README.md

@@ -211,6 +211,7 @@ information on what to include when reporting a bug.
    monitor (#1806)
  - [Win32] Bugfix: The default restored window position was lost when creating a maximized
    window
+ - [Win32] Bugfix: `glfwMaximizeWindow` would make a hidden window visible
  - [Cocoa] Added support for `VK_EXT_metal_surface` (#1619)
  - [Cocoa] Added locating the Vulkan loader at runtime in an application bundle
  - [Cocoa] Moved main menu creation to GLFW initialization time (#1649)

src/win32_init.c

@@ -91,6 +91,8 @@ static GLFWbool loadLibraries(void)
         _glfwPlatformGetModuleSymbol(_glfw.win32.user32.instance, "GetDpiForWindow");
     _glfw.win32.user32.AdjustWindowRectExForDpi_ = (PFN_AdjustWindowRectExForDpi)
         _glfwPlatformGetModuleSymbol(_glfw.win32.user32.instance, "AdjustWindowRectExForDpi");
+    _glfw.win32.user32.GetSystemMetricsForDpi_ = (PFN_GetSystemMetricsForDpi)
+        _glfwPlatformGetModuleSymbol(_glfw.win32.user32.instance, "GetSystemMetricsForDpi");
 
     _glfw.win32.dinput8.instance = _glfwPlatformLoadModule("dinput8.dll");
     if (_glfw.win32.dinput8.instance)

src/win32_platform.h

@@ -283,12 +283,14 @@ typedef BOOL (WINAPI * PFN_EnableNonClientDpiScaling)(HWND);
 typedef BOOL (WINAPI * PFN_SetProcessDpiAwarenessContext)(HANDLE);
 typedef UINT (WINAPI * PFN_GetDpiForWindow)(HWND);
 typedef BOOL (WINAPI * PFN_AdjustWindowRectExForDpi)(LPRECT,DWORD,BOOL,DWORD,UINT);
+typedef int (WINAPI * PFN_GetSystemMetricsForDpi)(int,UINT);
 #define SetProcessDPIAware _glfw.win32.user32.SetProcessDPIAware_
 #define ChangeWindowMessageFilterEx _glfw.win32.user32.ChangeWindowMessageFilterEx_
 #define EnableNonClientDpiScaling _glfw.win32.user32.EnableNonClientDpiScaling_
 #define SetProcessDpiAwarenessContext _glfw.win32.user32.SetProcessDpiAwarenessContext_
 #define GetDpiForWindow _glfw.win32.user32.GetDpiForWindow_
 #define AdjustWindowRectExForDpi _glfw.win32.user32.AdjustWindowRectExForDpi_
+#define GetSystemMetricsForDpi _glfw.win32.user32.GetSystemMetricsForDpi_
 
 // dwmapi.dll function pointer typedefs
 typedef HRESULT (WINAPI * PFN_DwmIsCompositionEnabled)(BOOL*);
@@ -471,6 +473,7 @@ typedef struct _GLFWlibraryWin32
         PFN_SetProcessDpiAwarenessContext SetProcessDpiAwarenessContext_;
         PFN_GetDpiForWindow             GetDpiForWindow_;
         PFN_AdjustWindowRectExForDpi    AdjustWindowRectExForDpi_;
+        PFN_GetSystemMetricsForDpi      GetSystemMetricsForDpi_;
     } user32;
 
     struct {

src/win32_window.c

@@ -484,6 +484,59 @@ static void releaseMonitor(_GLFWwindow* window)
     _glfwRestoreVideoModeWin32(window->monitor);
 }
 
+// Manually maximize the window, for when SW_MAXIMIZE cannot be used
+//
+static void maximizeWindowManually(_GLFWwindow* window)
+{
+    RECT rect;
+    DWORD style;
+    MONITORINFO mi = { sizeof(mi) };
+
+    GetMonitorInfo(MonitorFromWindow(window->win32.handle,
+                                     MONITOR_DEFAULTTONEAREST), &mi);
+
+    rect = mi.rcWork;
+
+    if (window->maxwidth != GLFW_DONT_CARE && window->maxheight != GLFW_DONT_CARE)
+    {
+        if (rect.right - rect.left > window->maxwidth)
+            rect.right = rect.left + window->maxwidth;
+        if (rect.bottom - rect.top > window->maxheight)
+            rect.bottom = rect.top + window->maxheight;
+    }
+
+    style = GetWindowLongW(window->win32.handle, GWL_STYLE);
+    style |= WS_MAXIMIZE;
+    SetWindowLongW(window->win32.handle, GWL_STYLE, style);
+
+    if (window->decorated)
+    {
+        const DWORD exStyle = GetWindowLongW(window->win32.handle, GWL_EXSTYLE);
+
+        if (_glfwIsWindows10AnniversaryUpdateOrGreaterWin32())
+        {
+            const UINT dpi = GetDpiForWindow(window->win32.handle);
+            AdjustWindowRectExForDpi(&rect, style, FALSE, exStyle, dpi);
+            OffsetRect(&rect, 0, GetSystemMetricsForDpi(SM_CYCAPTION, dpi));
+        }
+        else
+        {
+            AdjustWindowRectEx(&rect, style, FALSE, exStyle);
+            OffsetRect(&rect, 0, GetSystemMetrics(SM_CYCAPTION));
+        }
+
+        if (rect.bottom > mi.rcWork.bottom)
+            rect.bottom = mi.rcWork.bottom;
+    }
+
+    SetWindowPos(window->win32.handle, HWND_TOP,
+                 rect.left,
+                 rect.top,
+                 rect.right - rect.left,
+                 rect.bottom - rect.top,
+                 SWP_NOACTIVATE | SWP_NOZORDER | SWP_FRAMECHANGED);
+}
+
 // Window callback function (handles window messages)
 //
 static LRESULT CALLBACK windowProc(HWND hWnd, UINT uMsg,
@@ -1688,7 +1741,10 @@ void _glfwRestoreWindowWin32(_GLFWwindow* window)
 
 void _glfwMaximizeWindowWin32(_GLFWwindow* window)
 {
+    if (IsWindowVisible(window->win32.handle))
         ShowWindow(window->win32.handle, SW_MAXIMIZE);
+    else
+        maximizeWindowManually(window);
 }
 
 void _glfwShowWindowWin32(_GLFWwindow* window)