theme_windows.go

//go:build windows

package main

import (
	"syscall"
	"unsafe"

	"github.com/lxn/win"
	"golang.org/x/sys/windows/registry"
)

// prefersDark reports whether the user selected the dark app theme.
func prefersDark() bool {
	k, err := registry.OpenKey(registry.CURRENT_USER,
		`Software\Microsoft\Windows\CurrentVersion\Themes\Personalize`, registry.QUERY_VALUE)
	if err != nil {
		return false
	}
	defer k.Close()
	v, _, err := k.GetIntegerValue("AppsUseLightTheme")
	if err != nil {
		return false
	}
	return v == 0
}

var procDwmSetWindowAttribute = syscall.NewLazyDLL("dwmapi.dll").NewProc("DwmSetWindowAttribute")

// applyDarkTitleBar switches the window title bar to dark (Windows 10 20H1+/11).
// Best-effort; silently ignored on older systems.
func applyDarkTitleBar(hwnd win.HWND, dark bool) {
	var enabled int32
	if dark {
		enabled = 1
	}
	// DWMWA_USE_IMMERSIVE_DARK_MODE: 20 on current builds, 19 on early Win10 2004.
	for _, attr := range []uintptr{20, 19} {
		procDwmSetWindowAttribute.Call(uintptr(hwnd), attr,
			uintptr(unsafe.Pointer(&enabled)), unsafe.Sizeof(enabled))
	}
}