feat: start fullscreen no-WFB display at boot

cmd/groundstation-display/main.go

@@ -0,0 +1,71 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"os/exec"
+
+	"github.com/BurntSushi/xgb"
+	"github.com/BurntSushi/xgb/xproto"
+)
+
+const (
+	width  = 1920
+	height = 1080
+)
+
+func main() {
+	conn, err := xgb.NewConn()
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer conn.Close()
+
+	screen := xproto.Setup(conn).DefaultScreen(conn)
+	window, err := xproto.NewWindowId(conn)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	values := uint32(xproto.CwBackPixel | xproto.CwEventMask)
+	xproto.CreateWindow(conn, screen.RootDepth, window, screen.Root, 0, 0, width, height, 0,
+		xproto.WindowClassInputOutput, screen.RootVisual, values,
+		[]uint32{screen.BlackPixel, xproto.EventMaskExposure})
+	xproto.MapWindow(conn, window)
+	conn.Sync()
+
+	// XFCE owns the actual fullscreen policy; use its existing wmctrl helper.
+	_ = exec.Command("wmctrl", "-i", "-r", fmt.Sprintf("0x%08x", window), "-b", "add,fullscreen").Run()
+
+	gc, err := xproto.NewGcontextId(conn)
+	if err != nil {
+		log.Fatal(err)
+	}
+	xproto.CreateGC(conn, gc, xproto.Drawable(window), xproto.GcForeground|xproto.GcBackground,
+		[]uint32{screen.WhitePixel, screen.BlackPixel})
+	font := xproto.Font(window)
+	xproto.OpenFont(conn, font, uint16(len("fixed")), "fixed")
+	xproto.ChangeGC(conn, gc, xproto.GcFont, []uint32{uint32(font)})
+
+	draw := func() {
+		xproto.ClearArea(conn, false, window, 0, 0, width, height)
+		message := "Brak polaczenia WFB"
+		xproto.ImageText8(conn, byte(len(message)), xproto.Drawable(window), gc, 32, 56, message)
+		conn.Sync()
+	}
+	draw()
+
+	for {
+		event, err := conn.WaitForEvent()
+		if err != nil {
+			if os.IsTimeout(err) {
+				continue
+			}
+			return
+		}
+		if _, ok := event.(xproto.ExposeEvent); ok {
+			draw()
+		}
+	}
+}