From 8d9c1063aba135afbbbbcdabad0a479525976c09 Mon Sep 17 00:00:00 2001
From: Andy Williams <andy@andywilliams.me>
Date: Sat, 22 May 2021 15:12:25 +0100
Subject: [PATCH] Cherry picking Windows 10 theme workaround for dark mode

Fixes #2184
---
 internal/driver/glfw/window.go                |  7 +--
 .../{window_other.go => window_notlinux.go}   |  0
 internal/driver/glfw/window_notwindows.go     |  6 +++
 internal/driver/glfw/window_windows.go        | 43 +++++++++++++++++++
 4 files changed, 53 insertions(+), 3 deletions(-)
 rename internal/driver/glfw/{window_other.go => window_notlinux.go} (100%)
 create mode 100644 internal/driver/glfw/window_notwindows.go
 create mode 100644 internal/driver/glfw/window_windows.go

diff --git a/internal/driver/glfw/window.go b/internal/driver/glfw/window.go
index b37c5872e3..2624f24e3f 100644
--- a/internal/driver/glfw/window.go
+++ b/internal/driver/glfw/window.go
@@ -1,6 +1,5 @@
 package glfw
 
-import "C"
 import (
 	"bytes"
 	"context"
@@ -10,6 +9,8 @@ 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"
@@ -17,8 +18,6 @@ import (
 	"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)
diff --git a/internal/driver/glfw/window_other.go b/internal/driver/glfw/window_notlinux.go
similarity index 100%
rename from internal/driver/glfw/window_other.go
rename to internal/driver/glfw/window_notlinux.go
diff --git a/internal/driver/glfw/window_notwindows.go b/internal/driver/glfw/window_notwindows.go
new file mode 100644
index 0000000000..e5233c26f4
--- /dev/null
+++ b/internal/driver/glfw/window_notwindows.go
@@ -0,0 +1,6 @@
+// +build !windows
+
+package glfw
+
+func (w *window) setDarkMode() {
+}
diff --git a/internal/driver/glfw/window_windows.go b/internal/driver/glfw/window_windows.go
new file mode 100644
index 0000000000..9b72799872
--- /dev/null
+++ b/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
+}