Default to fullscreen mode on Steam Deck

flags.go

@@ -86,6 +86,10 @@ func parseFlags() *game.Game {
 	flag.IntVar(&debug, "debug", 0, "Debug level")
 	flag.Parse()
 
+	if game.DefaultFullscreen() {
+		fullscreen = true
+	}
+
 	var forceLanguage *language.Tag
 	if locale == "" {
 		var err error

game/platform_android.go

@@ -29,3 +29,7 @@ func GetLocale() (string, error) {
 	}
 	return string(out), nil
 }
+
+func DefaultFullscreen() bool {
+	return false
+}

game/platform_linux.go

@@ -3,9 +3,20 @@
 package game
 
 import (
+	"bytes"
 	"os"
 )
 
 func GetLocale() (string, error) {
 	return os.Getenv("LANG"), nil
 }
+
+func DefaultFullscreen() bool {
+	buf, err := os.ReadFile("/sys/devices/virtual/dmi/id/board_vendor")
+	if err != nil {
+		return false
+	}
+
+	steamDevice := bytes.Equal(bytes.ToLower(bytes.TrimSpace(buf)), []byte("valve"))
+	return steamDevice // Default to fullscreen mode on Steam Deck.
+}

game/platform_wasm.go

@@ -7,3 +7,7 @@ import "syscall/js"
 func GetLocale() (string, error) {
 	return js.Global().Get("navigator").Get("language").String(), nil
 }
+
+func DefaultFullscreen() bool {
+	return false
+}

game/platform_windows.go

@@ -0,0 +1,7 @@
+//go:build windows
+
+package game
+
+func DefaultFullscreen() bool {
+	return false
+}