Add new example: squirals (#952)

.gitignore

@@ -2,3 +2,4 @@
 *~
 *.aar
 *.apk
+.vscode

examples/squiral/main.go

@@ -0,0 +1,351 @@
+// Copyright 2019 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
+
+// This demo is inspired by the xscreensaver 'squirals'.
+
+package main
+
+import (
+	"fmt"
+	"image/color"
+	"math/rand"
+	"time"
+
+	"github.com/hajimehoshi/ebiten"
+	"github.com/hajimehoshi/ebiten/ebitenutil"
+	"github.com/hajimehoshi/ebiten/inpututil"
+)
+
+const (
+	width         = 800
+	height        = 600
+	scale         = 1
+	numOfSquirals = width / 32
+)
+
+type palette struct {
+	name   string
+	colors []color.Color
+}
+
+var (
+	background = color.Black
+
+	palettes = []palette{
+		{
+			name: "sand dunes",
+			colors: []color.Color{
+				color.RGBA{0xF2, 0x74, 0x05, 0xFF}, // #F27405
+				color.RGBA{0xD9, 0x52, 0x04, 0xFF}, // #D95204
+				color.RGBA{0x40, 0x18, 0x01, 0xFF}, // #401801
+				color.RGBA{0xA6, 0x2F, 0x03, 0xFF}, // #A62F03
+				color.RGBA{0x73, 0x2A, 0x19, 0xFF}, // #732A19
+			},
+		},
+		{
+			name: "mono desert sand",
+			colors: []color.Color{
+				color.RGBA{0x7F, 0x6C, 0x52, 0xFF}, // #7F6C52
+				color.RGBA{0xFF, 0xBA, 0x58, 0xFF}, // #FFBA58
+				color.RGBA{0xFF, 0xD9, 0xA5, 0xFF}, // #FFD9A5
+				color.RGBA{0x7F, 0x50, 0x0F, 0xFF}, // #7F500F
+				color.RGBA{0xCC, 0xAE, 0x84, 0xFF}, // #CCAE84
+			},
+		},
+		{
+			name: "land sea gradient",
+			colors: []color.Color{
+				color.RGBA{0x00, 0xA2, 0xE8, 0xFF}, // #00A2E8
+				color.RGBA{0x67, 0xA3, 0xF5, 0xFF}, // #67A3F5
+				color.RGBA{0xFF, 0xFF, 0xD5, 0xFF}, // #FFFFD5
+				color.RGBA{0xDD, 0xE8, 0x0C, 0xFF}, // #DDE80C
+				color.RGBA{0x74, 0x9A, 0x0D, 0xFF}, // #749A0D
+			},
+		},
+	}
+	selectedPalette = 0
+	colorCycle      = 0
+	canvas          *ebiten.Image
+	auto            *automaton
+	// blocker is an arbitrary color used to prevent the
+	// squirals from leaving the canvas.
+	blocker = color.RGBA{0, 0, 0, 254}
+
+	// dirCycles defines by offset which direction a squiral
+	// should try next for the two cases:
+	// clockwise:
+	//	1. try to turn right (index+1)
+	//  2. try to go straight (index+0)
+	//  3. try to turn left (index+3)
+	// counter-clockwise:
+	//  1. try to turn left (index+3)
+	//  2. try to go straight (index+0)
+	//  3. try to turn right (index+1)
+	dirCycles = [2][3]int{
+		[3]int{1, 0, 3}, // cw
+		[3]int{3, 0, 1}, // ccw
+	}
+
+	// dirs contains vectors for the directions: east, south, west, north
+	// in the specified order.
+	dirs = [4]vec2{vec2{1, 0}, vec2{0, 1}, vec2{-1, 0}, vec2{0, -1}}
+
+	// neighbors defines neighboring cells depending on the moving
+	// direction of the squiral:
+	// index of 0 -> squiral moves vertically,
+	// index of 1 -> squiral moves horizontally.
+	// These neighbors are tested for "collisions" during simulation.
+	neighbors = [2][2]vec2{
+		[2]vec2{vec2{0, 1}, vec2{0, -1}}, // east, west
+		[2]vec2{vec2{1, 0}, vec2{-1, 0}}, // south, north
+	}
+)
+
+type vec2 struct {
+	x int
+	y int
+}
+
+type squiral struct {
+	speed int
+	pos   vec2
+	dir   int
+	rot   int
+	col   color.Color
+	dead  bool
+}
+
+func (s *squiral) spawn() {
+	s.dead = false
+
+	rx := rand.Intn(width-4) + 2
+	ry := rand.Intn(height-4) + 2
+
+	for dx := -2; dx <= 2; dx++ {
+		for dy := -2; dy <= 2; dy++ {
+			tx, ty := rx+dx, ry+dy
+			if auto.colorMap[tx][ty] != background {
+				s.dead = true
+				return
+			}
+		}
+	}
+
+	s.speed = rand.Intn(5) + 1
+	s.pos.x = rx
+	s.pos.y = ry
+	s.dir = rand.Intn(4)
+
+	colorCycle = (colorCycle + 1) % len(palettes[selectedPalette].colors)
+	s.col = palettes[selectedPalette].colors[colorCycle]
+
+	s.rot = rand.Intn(2)
+}
+
+func (s *squiral) step(debug int) {
+	if s.dead {
+		return
+	}
+	x, y := s.pos.x, s.pos.y // shorthands
+
+	change := rand.Intn(1000)
+	if change < 2 {
+		// On 0.2% of iterations, switch rotation direction.
+		s.rot = (s.rot + 1) % 2
+	}
+
+	// 1. try to advance the spiral in its rotation
+	// direction (clockwise or counter-clockwise).
+	for _, next := range dirCycles[s.rot] {
+		dir := (s.dir + next) % 4
+		off := dirs[dir]
+		// Peek all targets by priority.
+		target := vec2{
+			x: x + off.x,
+			y: y + off.y,
+		}
+		if auto.colorMap[target.x][target.y] == background {
+			// If the target is free we need to also check the
+			// surrounding cells.
+
+			// a. Test if next cell in direction dir does not have
+			// the same color as this squiral.
+			ntarg := vec2{
+				x: target.x + off.x,
+				y: target.y + off.y,
+			}
+			if auto.colorMap[ntarg.x][ntarg.y] == s.col {
+				// If this has the same color, we cannot go into this direction,
+				// to avoid ugly blocks of equal color.
+				continue // try next direction
+			}
+
+			// b. Test all outer fields for the color of the
+			// squiral itself.
+			horivert := dir % 2
+			xtarg := vec2{}
+			set := true
+			for _, out := range neighbors[horivert] {
+				xtarg.x = target.x + out.x
+				xtarg.y = target.y + out.y
+
+				// If one of the outer targets equals the squiral's
+				// color, again continue with next direction.
+				if auto.colorMap[xtarg.x][xtarg.y] == s.col {
+					// If this is not free we cannot go into this direction.
+					set = false
+					break // try next direction
+				}
+
+				xtarg.x = ntarg.x + out.x
+				xtarg.y = ntarg.y + out.y
+
+				// If one of the outer targets equals the squiral's
+				// color, again continue with next direction.
+				if auto.colorMap[xtarg.x][xtarg.y] == s.col {
+					// If this is not free we cannot go into this direction.
+					set = false
+					break // try next direction
+				}
+			}
+
+			if set {
+				s.pos = target
+				s.dir = dir
+				// 2. set the color of this squiral to its
+				// current position.
+				setpix(s.pos, s.col)
+				return
+			}
+		}
+	}
+
+	s.dead = true
+}
+
+type automaton struct {
+	squirals [numOfSquirals]squiral
+	colorMap [width][height]color.Color
+}
+
+func (au *automaton) init() {
+	// Init the test grid with color (0,0,0,0) and the borders of
+	// it with color(0,0,0,254) as a blocker color, so the squirals
+	// cannot escape the scene.
+	for x := 0; x < width; x++ {
+		for y := 0; y < height; y++ {
+			if x == 0 || x == width-1 || y == 0 || y == height-1 {
+				auto.colorMap[x][y] = blocker
+			} else {
+				auto.colorMap[x][y] = background
+			}
+		}
+	}
+
+	for i := 0; i < numOfSquirals; i++ {
+		auto.squirals[i].spawn()
+	}
+}
+
+func (au *automaton) step() {
+	for i := 0; i < numOfSquirals; i++ {
+		for s := 0; s < au.squirals[i].speed; s++ {
+			au.squirals[i].step(i)
+			if au.squirals[i].dead {
+				au.squirals[i].spawn()
+			}
+		}
+	}
+}
+
+func setpix(xy vec2, col color.Color) {
+	canvas.Set(xy.x, xy.y, col)
+	auto.colorMap[xy.x][xy.y] = col
+}
+
+func init() {
+	rand.Seed(time.Now().UnixNano())
+	c, _ := ebiten.NewImage(width, height, ebiten.FilterDefault)
+	canvas = c
+	canvas.Fill(background)
+
+	auto = &automaton{}
+	auto.init()
+}
+
+func update(screen *ebiten.Image) error {
+	reset := false
+
+	if inpututil.IsKeyJustPressed(ebiten.KeyB) {
+		if background == color.White {
+			background = color.Black
+		} else {
+			background = color.White
+		}
+		reset = true
+	} else if inpututil.IsKeyJustPressed(ebiten.KeyT) {
+		selectedPalette = (selectedPalette + 1) % len(palettes)
+		reset = true
+	} else if inpututil.IsKeyJustPressed(ebiten.KeyR) {
+		reset = true
+	}
+
+	if reset {
+		canvas.Fill(background)
+		auto.init()
+	}
+
+	auto.step()
+
+	if ebiten.IsDrawingSkipped() {
+		return nil
+	}
+
+	draw(screen)
+
+	return nil
+}
+
+func draw(screen *ebiten.Image) {
+	screen.DrawImage(canvas, nil)
+	ebitenutil.DebugPrintAt(
+		screen,
+		fmt.Sprintf("TPS: %0.2f, FPS: %0.2f", ebiten.CurrentTPS(), ebiten.CurrentFPS()),
+		1, 0,
+	)
+	ebitenutil.DebugPrintAt(
+		screen,
+		"[r]: respawn",
+		1, 16,
+	)
+	ebitenutil.DebugPrintAt(
+		screen,
+		"[b]: toggle background (white/black)",
+		1, 32,
+	)
+	ebitenutil.DebugPrintAt(
+		screen,
+		fmt.Sprintf("[t]: cycle theme (current: %s)", palettes[selectedPalette].name),
+		1, 48,
+	)
+}
+
+func main() {
+	ebiten.SetMaxTPS(250)
+	if err := ebiten.Run(update, width, height, scale, "Squirals"); err != nil {
+		panic(err)
+	}
+}