examples: Add a snake game (#1276)

examples/snake/main.go

@@ -0,0 +1,208 @@
+// Copyright 2020 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.
+
+// +build example jsgo
+
+package main
+
+import (
+	"fmt"
+	"image/color"
+	"log"
+	"math/rand"
+	"time"
+
+	"github.com/hajimehoshi/ebiten"
+	"github.com/hajimehoshi/ebiten/ebitenutil"
+	"github.com/hajimehoshi/ebiten/inpututil"
+)
+
+const (
+	screenWidth  = 640
+	screenHeight = 480
+	gridSize     = 10
+	xNumInScreen = screenWidth / gridSize
+	yNumInScreen = screenHeight / gridSize
+)
+
+const (
+	dirNone = iota
+	dirLeft
+	dirRight
+	dirDown
+	dirUp
+)
+
+type Position struct {
+	X int
+	Y int
+}
+
+type Game struct {
+	moveDirection int
+	snakeBody     []Position
+	apple         Position
+	timer         int
+	moveTime      int
+	score         int
+	bestScore     int
+	level         int
+}
+
+func init() {
+	rand.Seed(time.Now().UnixNano())
+}
+
+func (g *Game) collidesWithApple() bool {
+	return g.snakeBody[0].X == g.apple.X &&
+		g.snakeBody[0].Y == g.apple.Y
+}
+
+func (g *Game) collidesWithSelf() bool {
+	for _, v := range g.snakeBody[1:] {
+		if g.snakeBody[0].X == v.X &&
+			g.snakeBody[0].Y == v.Y {
+			return true
+		}
+	}
+	return false
+}
+
+func (g *Game) collidesWithWall() bool {
+	return g.snakeBody[0].X < 0 ||
+		g.snakeBody[0].Y < 0 ||
+		g.snakeBody[0].X >= xNumInScreen ||
+		g.snakeBody[0].Y >= yNumInScreen
+}
+
+func (g *Game) needsToMoveSnake() bool {
+	return g.timer%g.moveTime == 0
+}
+
+func (g *Game) reset() {
+	g.apple.X = 3 * gridSize
+	g.apple.Y = 3 * gridSize
+	g.moveTime = 4
+	g.snakeBody = g.snakeBody[:1]
+	g.snakeBody[0].X = xNumInScreen / 2
+	g.snakeBody[0].Y = yNumInScreen / 2
+	g.score = 0
+	g.level = 1
+	g.moveDirection = dirNone
+}
+
+func (g *Game) Update(screen *ebiten.Image) error {
+	if inpututil.IsKeyJustPressed(ebiten.KeyLeft) || inpututil.IsKeyJustPressed(ebiten.KeyA) {
+		if g.moveDirection != dirRight {
+			g.moveDirection = dirLeft
+		}
+	} else if inpututil.IsKeyJustPressed(ebiten.KeyRight) || inpututil.IsKeyJustPressed(ebiten.KeyD) {
+		if g.moveDirection != dirLeft {
+			g.moveDirection = dirRight
+		}
+	} else if inpututil.IsKeyJustPressed(ebiten.KeyDown) || inpututil.IsKeyJustPressed(ebiten.KeyS) {
+		if g.moveDirection != dirUp {
+			g.moveDirection = dirDown
+		}
+	} else if inpututil.IsKeyJustPressed(ebiten.KeyUp) || inpututil.IsKeyJustPressed(ebiten.KeyW) {
+		if g.moveDirection != dirDown {
+			g.moveDirection = dirUp
+		}
+	} else if inpututil.IsKeyJustPressed(ebiten.KeyEscape) {
+		g.reset()
+	}
+
+	if g.needsToMoveSnake() {
+		if g.collidesWithWall() || g.collidesWithSelf() {
+			g.reset()
+		}
+
+		if g.collidesWithApple() {
+			g.apple.X = rand.Intn(xNumInScreen - 1)
+			g.apple.Y = rand.Intn(yNumInScreen - 1)
+			g.snakeBody = append(g.snakeBody, Position{
+				X: g.snakeBody[len(g.snakeBody)-1].X,
+				Y: g.snakeBody[len(g.snakeBody)-1].Y,
+			})
+			if len(g.snakeBody) > 10 && len(g.snakeBody) < 20 {
+				g.level = 2
+				g.moveTime = 3
+			} else if len(g.snakeBody) > 20 {
+				g.level = 3
+				g.moveTime = 2
+			} else {
+				g.level = 1
+			}
+			g.score++
+			if g.bestScore < g.score {
+				g.bestScore = g.score
+			}
+		}
+
+		for i := int64(len(g.snakeBody)) - 1; i > 0; i-- {
+			g.snakeBody[i].X = g.snakeBody[i-1].X
+			g.snakeBody[i].Y = g.snakeBody[i-1].Y
+		}
+		switch g.moveDirection {
+		case dirLeft:
+			g.snakeBody[0].X--
+		case dirRight:
+			g.snakeBody[0].X++
+		case dirDown:
+			g.snakeBody[0].Y++
+		case dirUp:
+			g.snakeBody[0].Y--
+		}
+	}
+
+	g.timer++
+
+	return nil
+}
+
+func (g *Game) Draw(screen *ebiten.Image) {
+	for _, v := range g.snakeBody {
+		ebitenutil.DrawRect(screen, float64(v.X*gridSize), float64(v.Y*gridSize), gridSize, gridSize, color.RGBA{0x80, 0xa0, 0xc0, 0xff})
+	}
+	ebitenutil.DrawRect(screen, float64(g.apple.X*gridSize), float64(g.apple.Y*gridSize), gridSize, gridSize, color.RGBA{0xFF, 0x00, 0x00, 0xff})
+
+	if g.moveDirection == dirNone {
+		ebitenutil.DebugPrint(screen, fmt.Sprintf("Press up/down/left/right to start"))
+	} else {
+		ebitenutil.DebugPrint(screen, fmt.Sprintf("FPS: %0.2f Level: %d Score: %d Best Score: %d", ebiten.CurrentFPS(), g.level, g.score, g.bestScore))
+	}
+}
+
+func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
+	return screenWidth, screenHeight
+}
+
+func newGame() *Game {
+	g := &Game{
+		apple:     Position{X: 3 * gridSize, Y: 3 * gridSize},
+		moveTime:  4,
+		snakeBody: make([]Position, 1),
+	}
+	g.snakeBody[0].X = xNumInScreen / 2
+	g.snakeBody[0].Y = yNumInScreen / 2
+	return g
+}
+
+func main() {
+	ebiten.SetWindowSize(screenWidth, screenHeight)
+	ebiten.SetWindowTitle("Snake (Ebiten Demo)")
+	if err := ebiten.RunGame(newGame()); err != nil {
+		log.Fatal(err)
+	}
+}