Add option to set OS dark theme

docs/window.md

@@ -262,6 +262,11 @@ This is the new name, introduced in GLFW 3.4.  The older
 `GLFW_COCOA_RETINA_FRAMEBUFFER` name is also available for compatibility.  Both
 names modify the same hint value.
 
+@anchor GLFW_THEME
+__GLFW_THEME__ specifies whether the window should use light theme or not.
+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
 __GLFW_MOUSE_PASSTHROUGH__ specifies whether the window is transparent to mouse
 input, letting any mouse events pass through to whatever window is behind it.

include/GLFW/glfw3.h

@@ -1108,6 +1108,11 @@ extern "C" {
  *  [GLFW_SCALE_FRAMEBUFFER](@ref GLFW_SCALE_FRAMEBUFFER_hint) window hint for
  *  compatibility with earlier versions.
  */
+#define GLFW_THEME                  0x0002200E
+/*! @brief windows specific
+ *
+ *  Allows specifying whether light or dark theme should be used.
+ */
 #define GLFW_COCOA_RETINA_FRAMEBUFFER 0x00023001
 /*! @brief macOS specific
  *  [window hint](@ref GLFW_COCOA_FRAME_NAME_hint).
@@ -1182,6 +1187,10 @@ 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.
  *
@@ -3480,6 +3489,8 @@ GLFWAPI void glfwGetWindowPos(GLFWwindow* window, int* xpos, int* ypos);
  */
 GLFWAPI void glfwSetWindowPos(GLFWwindow* window, int xpos, int ypos);
 
+GLFWAPI int glfwIsWindowLightTheme(GLFWwindow* window);
+
 /*! @brief Retrieves the size of the content area of the specified window.
  *
  *  This function retrieves the size, in screen coordinates, of the content area

src/internal.h

@@ -415,6 +415,7 @@ struct _GLFWwndconfig
     GLFWbool      mousePassthrough;
     GLFWbool      scaleToMonitor;
     GLFWbool      scaleFramebuffer;
+    int           theme;
     struct {
         char      frameName[256];
     } ns;
@@ -539,6 +540,7 @@ struct _GLFWwindow
     GLFWbool            focusOnShow;
     GLFWbool            mousePassthrough;
     GLFWbool            shouldClose;
+    GLFWbool            isLightTheme;
     void*               userPointer;
     GLFWbool            doublebuffer;
     GLFWvidmode         videoMode;

src/win32_init.c

@@ -149,6 +149,8 @@ static GLFWbool loadLibraries(void)
             _glfwPlatformGetModuleSymbol(_glfw.win32.dwmapi.instance, "DwmEnableBlurBehindWindow");
         _glfw.win32.dwmapi.GetColorizationColor = (PFN_DwmGetColorizationColor)
             _glfwPlatformGetModuleSymbol(_glfw.win32.dwmapi.instance, "DwmGetColorizationColor");
+        _glfw.win32.dwmapi.DwmSetWindowAttribute = (PFN_DwmSetWindowAttribute)
+            _glfwPlatformGetModuleSymbol(_glfw.win32.dwmapi.instance, "DwmSetWindowAttribute");
     }
 
     _glfw.win32.shcore.instance = _glfwPlatformLoadModule("shcore.dll");
@@ -567,6 +569,14 @@ void _glfwUpdateKeyNamesWin32(void)
     }
 }
 
+void _glfwSetWindowTheme(BOOL dark, HWND hwnd)
+{
+#ifndef DWMWA_USE_IMMERSIVE_DARK_MODE
+#define DWMWA_USE_IMMERSIVE_DARK_MODE 20
+#endif
+    _glfw.win32.dwmapi.DwmSetWindowAttribute(hwnd, DWMWA_USE_IMMERSIVE_DARK_MODE, &dark, sizeof(dark));
+}
+
 // Replacement for IsWindowsVersionOrGreater, as we cannot rely on the
 // application having a correct embedded manifest
 //

src/win32_platform.h

@@ -286,6 +286,7 @@ typedef HRESULT (WINAPI * PFN_DwmIsCompositionEnabled)(BOOL*);
 typedef HRESULT (WINAPI * PFN_DwmFlush)(VOID);
 typedef HRESULT (WINAPI * PFN_DwmEnableBlurBehindWindow)(HWND,const DWM_BLURBEHIND*);
 typedef HRESULT (WINAPI * PFN_DwmGetColorizationColor)(DWORD*,BOOL*);
+typedef HRESULT (WINAPI * PFN_DwmSetWindowAttribute)(HWND, DWORD, LPCVOID, DWORD);
 #define DwmIsCompositionEnabled _glfw.win32.dwmapi.IsCompositionEnabled
 #define DwmFlush _glfw.win32.dwmapi.Flush
 #define DwmEnableBlurBehindWindow _glfw.win32.dwmapi.EnableBlurBehindWindow
@@ -475,6 +476,7 @@ typedef struct _GLFWlibraryWin32
         PFN_DwmFlush                    Flush;
         PFN_DwmEnableBlurBehindWindow   EnableBlurBehindWindow;
         PFN_DwmGetColorizationColor     GetColorizationColor;
+        PFN_DwmSetWindowAttribute       DwmSetWindowAttribute;
     } dwmapi;
 
     struct {
@@ -521,6 +523,7 @@ BOOL _glfwIsWindowsVersionOrGreaterWin32(WORD major, WORD minor, WORD sp);
 BOOL _glfwIsWindows10BuildOrGreaterWin32(WORD build);
 void _glfwInputErrorWin32(int error, const char* description);
 void _glfwUpdateKeyNamesWin32(void);
+void _glfwSetWindowTheme(BOOL dark, HWND hwnd);
 
 void _glfwPollMonitorsWin32(void);
 void _glfwSetVideoModeWin32(_GLFWmonitor* monitor, const GLFWvidmode* desired);

src/win32_window.c

@@ -1396,6 +1396,36 @@ static int createNativeWindow(_GLFWwindow* window,
                                            _glfw.win32.instance,
                                            (LPVOID) wndconfig);
 
+    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);
+    window->isLightTheme = should_use_light_mode ? GLFW_TRUE : GLFW_FALSE;
+
     _glfw_free(wideTitle);
 
     if (!window->win32.handle)

src/window.c

@@ -388,6 +388,8 @@ GLFWAPI void glfwWindowHint(int hint, int value)
         case GLFW_SCALE_FRAMEBUFFER:
         case GLFW_COCOA_RETINA_FRAMEBUFFER:
             _glfw.hints.window.scaleFramebuffer = value ? GLFW_TRUE : GLFW_FALSE;
+        case GLFW_THEME:
+            _glfw.hints.window.theme = value;
             return;
         case GLFW_CENTER_CURSOR:
             _glfw.hints.window.centerCursor = value ? GLFW_TRUE : GLFW_FALSE;
@@ -607,6 +609,15 @@ GLFWAPI void glfwSetWindowPos(GLFWwindow* handle, int xpos, int ypos)
     _glfw.platform.setWindowPos(window, xpos, ypos);
 }
 
+GLFWAPI int glfwIsWindowLightTheme(GLFWwindow* handle)
+{
+    _GLFWwindow* window = (_GLFWwindow*)handle;
+    assert(window != NULL);
+
+    _GLFW_REQUIRE_INIT_OR_RETURN(0);
+    return window->isLightTheme;
+}
+
 GLFWAPI void glfwGetWindowSize(GLFWwindow* handle, int* width, int* height)
 {
     if (width)