Add examples/life (#182)

examples/life/README.md

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+# Conway's Game of Life
+
+The original project is [martinlindhe/gol](https://github.com/martinlindhe/gol) by Martin Lindhe.
+
+## License
+
+MIT

examples/life/main.go

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+// The MIT License (MIT)
+//
+// Copyright (c) 2015-2016 Martin Lindhe
+// Copyright (c) 2016      Hajime Hoshi
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+package main
+
+import (
+	"image"
+	"log"
+	"math/rand"
+	"time"
+
+	"github.com/hajimehoshi/ebiten"
+)
+
+var (
+	randSource = rand.NewSource(time.Now().UnixNano())
+	rnd        = rand.New(randSource)
+)
+
+// World represents the game state
+type World struct {
+	area [][]bool
+}
+
+// NewWorld creates a new world
+func NewWorld(width, height int) *World {
+	world := World{}
+	world.area = makeArea(width, height)
+	return &world
+}
+
+// RandomSeed inits world with a random state
+func (w *World) RandomSeed(limit int) {
+	height := len(w.area)
+	width := len(w.area[0])
+
+	for i := 0; i < limit; i++ {
+		x := rnd.Intn(width)
+		y := rnd.Intn(height)
+		w.area[y][x] = true
+	}
+}
+
+// Progress game state by one tick
+func (w *World) Progress() {
+	height := len(w.area)
+	width := len(w.area[0])
+
+	next := makeArea(width, height)
+
+	for y := 0; y < height; y++ {
+		for x := 0; x < width; x++ {
+
+			pop := neighbourCount(w.area, x, y)
+			switch {
+			case pop < 2:
+				// rule 1. Any live cell with fewer than two live neighbours
+				// dies, as if caused by under-population.
+				next[y][x] = false
+
+			case (pop == 2 || pop == 3) && w.area[y][x]:
+				// rule 2. Any live cell with two or three live neighbours
+				// lives on to the next generation.
+				next[y][x] = true
+
+			case pop > 3:
+				// rule 3. Any live cell with more than three live neighbours
+				// dies, as if by over-population.
+				next[y][x] = false
+
+			case pop == 3:
+				// rule 4. Any dead cell with exactly three live neighbours
+				// becomes a live cell, as if by reproduction.
+				next[y][x] = true
+			}
+		}
+	}
+	w.area = next
+}
+
+// DrawImage paints current game state
+func (w *World) DrawImage(img *image.RGBA) {
+	height := len(w.area)
+	width := len(w.area[0])
+
+	for y := 0; y < height; y++ {
+		for x := 0; x < width; x++ {
+			pos := 4*y*width + 4*x
+			if w.area[y][x] {
+				img.Pix[pos] = 0xff
+				img.Pix[pos+1] = 0xff
+				img.Pix[pos+2] = 0xff
+				img.Pix[pos+3] = 0xff
+			} else {
+				img.Pix[pos] = 0
+				img.Pix[pos+1] = 0
+				img.Pix[pos+2] = 0
+				img.Pix[pos+3] = 0
+			}
+		}
+	}
+}
+
+// neighbourCount calculates the Moore neighborhood of x, y
+func neighbourCount(a [][]bool, x, y int) int {
+	height := len(a)
+	width := len(a[0])
+
+	lowX := 0
+	if x > 0 {
+		lowX = x - 1
+	}
+
+	lowY := 0
+	if y > 0 {
+		lowY = y - 1
+	}
+
+	highX := width - 1
+	if x < width-1 {
+		highX = x + 1
+	}
+
+	highY := height - 1
+	if y < height-1 {
+		highY = y + 1
+	}
+
+	near := 0
+	for pY := lowY; pY <= highY; pY++ {
+		for pX := lowX; pX <= highX; pX++ {
+			if !(pX == x && pY == y) && a[pY][pX] {
+				near++
+			}
+		}
+	}
+
+	return near
+}
+
+func makeArea(width, height int) [][]bool {
+	area := make([][]bool, height)
+	for i := 0; i < height; i++ {
+		area[i] = make([]bool, width)
+	}
+	return area
+}
+
+const (
+	screenWidth  = 320
+	screenHeight = 240
+)
+
+var (
+	world      *World
+	noiseImage *image.RGBA
+)
+
+func update(screen *ebiten.Image) error {
+	world.Progress()
+	world.DrawImage(noiseImage)
+	screen.ReplacePixels(noiseImage.Pix)
+	return nil
+}
+
+func main() {
+	population := int((screenWidth * screenHeight) / 10)
+	scale := 2.0
+
+	world = NewWorld(screenWidth, screenHeight)
+	world.RandomSeed(population)
+
+	noiseImage = image.NewRGBA(image.Rect(0, 0, screenWidth, screenHeight))
+	if err := ebiten.Run(update, screenWidth, screenHeight, scale, "Game of Life (Ebiten Demo)"); err != nil {
+		log.Fatal(err)
+	}
+}