Cherry picking Windows 10 theme workaround for dark mode

Fixes #2184

internal/driver/glfw/window.go

@@ -1,6 +1,5 @@
 package glfw
 
-import "C"
 import (
 	"bytes"
 	"context"
@@ -10,15 +9,15 @@ import (
 	"sync"
 	"time"
 
+	"github.com/go-gl/glfw/v3.3/glfw"
+
 	"fyne.io/fyne/v2"
 	"fyne.io/fyne/v2/driver/desktop"
 	"fyne.io/fyne/v2/internal"
 	"fyne.io/fyne/v2/internal/cache"
 	"fyne.io/fyne/v2/internal/driver"
 	"fyne.io/fyne/v2/internal/painter/gl"
 	"fyne.io/fyne/v2/widget"
-
-	"github.com/go-gl/glfw/v3.3/glfw"
 )
 
 const (
@@ -1345,6 +1344,8 @@ func (w *window) create() {
 	})
 
 	runOnMain(func() {
+		w.setDarkMode()
+
 		win := w.view()
 		win.SetCloseCallback(w.closed)
 		win.SetPosCallback(w.moved)

internal/driver/glfw/window_notwindows.go

@@ -0,0 +1,6 @@
+// +build !windows
+
+package glfw
+
+func (w *window) setDarkMode() {
+}

internal/driver/glfw/window_windows.go

@@ -0,0 +1,43 @@
+package glfw
+
+import (
+	"runtime"
+	"syscall"
+	"unsafe"
+
+	"fyne.io/fyne/v2"
+	"golang.org/x/sys/windows/registry"
+)
+
+func (w *window) setDarkMode() {
+	if runtime.GOOS == "windows" {
+		hwnd := w.view().GetWin32Window()
+		dark := isDark()
+
+		dwm := syscall.NewLazyDLL("dwmapi.dll")
+		setAtt := dwm.NewProc("DwmSetWindowAttribute")
+		ret, _, err := setAtt.Call(uintptr(unsafe.Pointer(hwnd)), // window handle
+			20,                             // DWMWA_USE_IMMERSIVE_DARK_MODE
+			uintptr(unsafe.Pointer(&dark)), // on or off
+			8)                              // sizeof(darkMode)
+
+		if ret != 0 { // err is always non-nil, we check return value
+			fyne.LogError("Failed to set dark mode", err)
+		}
+	}
+}
+
+func isDark() bool {
+	k, err := registry.OpenKey(registry.CURRENT_USER, `SOFTWARE\Microsoft\Windows\CurrentVersion\Themes\Personalize`, registry.QUERY_VALUE)
+	if err != nil { // older version of Windows will not have this key
+		return false
+	}
+	defer k.Close()
+
+	useLight, _, err := k.GetIntegerValue("AppsUseLightTheme")
+	if err != nil { // older version of Windows will not have this value
+		return false
+	}
+
+	return useLight == 0
+}