Better window theme handling using windows registry

docs/window.dox

@@ -249,9 +249,9 @@ This hint only has an effect on platforms where screen coordinates and pixels
 always map 1:1 such as Windows and X11.  On platforms like macOS the resolution
 of the framebuffer is changed independently of the window size.
 
-@anchor GLFW_LIGHT_THEME
+@anchor GLFW_THEME
-__GLFW_LIGHT_THEME__ specifies whether the window should use light theme or not.
+__GLFW_THEME__ specifies whether the window should use light theme or not.
-Possible values are `GLFW_TRUE` and `GLFW_FALSE`. This hint only has effect
+Possible values are `GLFW_THEME_AUTO`, `GLFW_THEME_DARK`, and `GLFW_THEME_LIGHT`. This hint only has effect
 on windows operating system.
 
 @anchor GLFW_MOUSE_PASSTHROUGH_hint

include/GLFW/glfw3.h

@@ -1099,10 +1099,10 @@ extern "C" {
 /*! @brief macOS specific
  *  [window hint](@ref GLFW_COCOA_RETINA_FRAMEBUFFER_hint).
  */
-#define GLFW_LIGHT_THEME             0x0002200D
+#define GLFW_THEME                  0x0002200D
 /*! @brief windows specific
  *
- *  Allows specifying whether light theme should be used.
+ *  Allows specifying whether light or dark theme should be used.
  */
 #define GLFW_COCOA_RETINA_FRAMEBUFFER 0x00023001
 /*! @brief macOS specific
@@ -1174,6 +1174,10 @@ extern "C" {
 
 #define GLFW_ANY_POSITION           0x80000000
 
+#define GLFW_THEME_AUTO             0x00000000
+#define GLFW_THEME_DARK             0x00000001
+#define GLFW_THEME_LIGHT            0x00000002
+
 /*! @defgroup shapes Standard cursor shapes
  *  @brief Standard system cursor shapes.
  *

src/internal.h

@@ -408,7 +408,7 @@ struct _GLFWwndconfig
     GLFWbool      focusOnShow;
     GLFWbool      mousePassthrough;
     GLFWbool      scaleToMonitor;
-    GLFWbool      lightTheme;
+    int           theme;
     struct {
         GLFWbool  retina;
         char      frameName[256];

src/win32_window.c

@@ -1344,7 +1344,35 @@ static int createNativeWindow(_GLFWwindow* window,
                                            _glfw.win32.instance,
                                            (LPVOID) wndconfig);
 
-    _glfwSetWindowTheme(!(wndconfig->lightTheme), window->win32.handle);
+    BOOL should_use_light_mode;
+    if (wndconfig->theme == GLFW_THEME_AUTO)
+    {
+        BOOL success = FALSE;
+        HKEY hRootKey = HKEY_CURRENT_USER;
+        const wchar_t* lpSubKey = L"Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize";
+        const wchar_t* lpValueName = L"AppsUseLightTheme";
+        DWORD result;
+        {
+            HKEY hKey = 0;
+            if (RegOpenKeyExW(hRootKey, lpSubKey, 0, KEY_READ, &hKey) == ERROR_SUCCESS)
+            {
+                DWORD dwBufferSize = sizeof(DWORD);
+                DWORD dwData = 0;
+                if (RegQueryValueExW(hKey, lpValueName, 0, NULL, (LPBYTE)(&dwData), &dwBufferSize) == ERROR_SUCCESS)
+                {
+                    result = dwData;
+                    success = TRUE;
+                }
+                RegCloseKey(hKey);
+            }
+        }
+        should_use_light_mode = success && result != 0;
+    }
+    else
+        should_use_light_mode = wndconfig->theme == GLFW_THEME_LIGHT;
+
+    _glfwSetWindowTheme(!should_use_light_mode, window->win32.handle);
+
     _glfw_free(wideTitle);
 
     if (!window->win32.handle)

src/window.c

@@ -388,8 +388,8 @@ GLFWAPI void glfwWindowHint(int hint, int value)
         case GLFW_SCALE_TO_MONITOR:
             _glfw.hints.window.scaleToMonitor = value ? GLFW_TRUE : GLFW_FALSE;
             return;
-        case GLFW_LIGHT_THEME:
+        case GLFW_THEME:
-            _glfw.hints.window.lightTheme = value ? GLFW_TRUE : GLFW_FALSE;
+            _glfw.hints.window.theme = value;
             return;
         case GLFW_CENTER_CURSOR:
             _glfw.hints.window.centerCursor = value ? GLFW_TRUE : GLFW_FALSE;