ebiten/examples/typewriter/main.go

// Copyright 2017 The Ebiten Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package main

import (
	"log"
	"strings"

	"github.com/hajimehoshi/ebiten/v2"
	"github.com/hajimehoshi/ebiten/v2/ebitenutil"
	"github.com/hajimehoshi/ebiten/v2/inpututil"
)

const (
	screenWidth  = 640
	screenHeight = 480
)

// repeatingKeyPressed return true when key is pressed considering the repeat state.
func repeatingKeyPressed(key ebiten.Key) bool {
	const (
		delay    = 30
		interval = 3
	)
	d := inpututil.KeyPressDuration(key)
	if d == 1 {
		return true
	}
	if d >= delay && (d-delay)%interval == 0 {
		return true
	}
	return false
}

type Game struct {
	runes   []rune
	text    string
	counter int
}

func (g *Game) Update() error {
	// Add runes that are input by the user by AppendInputChars.
	// Note that AppendInputChars result changes every frame, so you need to call this
	// every frame.
	g.runes = ebiten.AppendInputChars(g.runes[:0])
	g.text += string(g.runes)

	// Adjust the string to be at most 10 lines.
	ss := strings.Split(g.text, "\n")
	if len(ss) > 10 {
		g.text = strings.Join(ss[len(ss)-10:], "\n")
	}

	// If the enter key is pressed, add a line break.
	if repeatingKeyPressed(ebiten.KeyEnter) || repeatingKeyPressed(ebiten.KeyNumpadEnter) {
		g.text += "\n"
	}

	// If the backspace key is pressed, remove one character.
	if repeatingKeyPressed(ebiten.KeyBackspace) {
		if len(g.text) >= 1 {
			g.text = g.text[:len(g.text)-1]
		}
	}

	g.counter++
	return nil
}

func (g *Game) Draw(screen *ebiten.Image) {
	// Blink the cursor.
	t := g.text
	if g.counter%60 < 30 {
		t += "_"
	}
	ebitenutil.DebugPrint(screen, t)
}

func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
	return screenWidth, screenHeight
}

func main() {
	g := &Game{
		text:    "Type on the keyboard:\n",
		counter: 0,
	}

	ebiten.SetWindowSize(screenWidth, screenHeight)
	ebiten.SetWindowTitle("TypeWriter (Ebitengine Demo)")
	if err := ebiten.RunGame(g); err != nil {
		log.Fatal(err)
	}
}