hello.go

package main

import (
	"fmt"
	"os"
	"time"

	"github.com/gdamore/tcell"
)

func printAt(s tcell.Screen, x int, y int, message string) {
	var mrune []rune
	for _, r := range message {
		mrune = append(mrune, r)
	}
	s.SetContent(x, y, mrune[0], mrune[1:], tcell.StyleDefault)
}

func initScreen() tcell.Screen {
	s, e := tcell.NewScreen()
	if e != nil {
		fmt.Fprintf(os.Stderr, "%v\n", e)
		os.Exit(1)
	}
	if e = s.Init(); e != nil {
		fmt.Fprintf(os.Stderr, "%v\n", e)
		os.Exit(1)
	}
	return s
}

func main() {
	s := initScreen()
	s.SetStyle(tcell.StyleDefault.
		Foreground(tcell.ColorBlack).
		Background(tcell.ColorWhite))
	s.Clear()
	w, h := s.Size()

	quit := make(chan struct{})
	go func() {
		for {
			ev := s.PollEvent()
			switch ev := ev.(type) {
			case *tcell.EventKey:
				switch ev.Key() {
				case tcell.KeyEscape, tcell.KeyEnter:
					close(quit)
					return
				case tcell.KeyCtrlL:
					s.Sync()
				}
			case *tcell.EventResize:
				s.Clear()
				s.Sync()
				w, h = s.Size()
			}
		}
	}()

	x, y := 0, 0
	xd, yd := 1, 1
	m := "Hello GO"
	lm := len(m)

loop:
	for {
		var p = fmt.Sprintf("w=%d h=%d x=%d y=%d   ", w, h, x, y)
		printAt(s, x, y, m)
		printAt(s, 0, 0, p)
		s.Show()
		select {
		case <-quit:
			break loop
		case <-time.After(time.Millisecond * 50):
		}
		//s.Clear()
		//s.Show()
		if x < 0 {
			x = -1
			xd = 1
		} else if x >= w-lm {
			x = w - lm - 1
			xd = -1
		}
		x += xd
		if y < 0 {
			yd = 1
			y = 0
		} else if y > h-1 {
			y = h - 1
			yd = -1
		}
		y += yd
	}
	s.Fini()
}