什么是贪吃蛇？
贪吃蛇（Snake）是起源于1976年的街机游戏 Blockade。此类游戏在1990年代由于一些具有小型屏幕的移动电话的引入而再度流行起来，在现在的手机上基本都可安装此小游戏。版本亦有所不同。
在游戏中，玩家操控一条细长的直线（俗称蛇或虫），它会不停前进，玩家只能操控蛇的头部朝向（上下左右），一路拾起触碰到之物（或称作“豆”），并要避免触碰到自身或者其他障碍物。每次贪吃蛇吃掉一个食物，它的身体便增长一些。吃掉一些食物后会使蛇的移动速度逐渐加快，让游戏的难度渐渐变大。游戏设计大致分为四面都有墙(都不可穿越)以及某部分的墙可以穿越，以及四面墙都可以穿越的模式。有些游戏碰到自己身体也不会死掉，例如蛇蛇食颜色、贪吃蛇进化论等等。本文将介绍如何用MoonBit实现贪吃蛇，完整的代码：https://github.com/moonbitlang/moonbit-docs/tree/main/examples/snake
如果你想尝试一下，可以点击此处进行尝试：https://www.moonbitlang.cn/gallery/snake/。
如何用MoonBit实现贪吃蛇
用struct GameState来创建整个游戏：
struct GameState{
mut grid: Array[Int]
mut body: List[Position]
mut dir: Direction
}
用grid来初始化每个格子的颜色：
0 0 0 0 0 0
0 2 0 1 0 0
0 0 0 0 0 0
0代表普通格子，1代表蛇的身体，2代表食物
初始化后的游戏界面：
生成食物
fn random() -> Double = "Math" "random"
fn floor(i: Double) -> Int = "Math" "floor"
fn generate_Food(self: GameState){
while true {
let i : Int = floor(random() * 20.0)
let j : Int = floor(random() * 20.0)
if(self.grid[j * grid_col_count + i] == grid_num(Default)){
self.setGridType({x: i, y: j}, Food)
return
}
}
}
首先通过两个外部引用函数随机生成新食物的横坐标和纵坐标，然后通过grid_num来判断新生成的坐标是否可以放置，最后通过setGridType方法来设置为食物。
控制蛇行进
pub fn tran_step(self : GameState, a : Int){
let mut action : Direction = Default
match a {
1 => action = Up
2 => action = Down
3 => action = Left
4 => action = Right
_ => action = Default
}
self.step(action)
}
pub fn step(self : GameState, action : Direction) {
match action {
// move up
Up =>{
if length(self.body) == 1{
self.dir = Up
}else{
if self.dir == Left || self.dir == Right || self.dir == Up{
self.dir = Up
}else{
self.dir = self.dir
}
}
}
// move down
Down =>{
if length(self.body) == 1{
self.dir = Down
}else{
if self.dir == Left || self.dir == Right || self.dir == Down{
self.dir = Down
}else{
self.dir = self.dir
}
}
}
// move left
Left =>{
if length(self.body) == 1{
self.dir = Left
}else{
if self.dir == Up || self.dir == Left || self.dir == Down{
self.dir = Left
}else{
self.dir = self.dir
}
}
}
// move right
Right =>{
if length(self.body) == 1{
self.dir = Right
}else{
if self.dir == Up || self.dir == Right || self.dir == Down{
self.dir = Right
}else{
self.dir = self.dir
}
}
}
_ =>{
self.dir = self.dir
}
}
self.go_step()
}
首先，step方法识别外部键盘的响应并对应不同的方向改变。然后，调用go_step方法完成蛇的移动
fn go_step(self: GameState, prev: Direction){
if (prev == Down && self.dir == Up ) || (prev == Up && self.dir == Down ) || (prev == Left && self.dir == Right ) || (prev == Right && self.dir == Left ){
self.dir = prev
}else {
self.dir = self.dir
}
let head : Position = get_head(self.body)
let newHead : Position = {x: head.x , y: head.y }
newHead.x = dir_posi(self.dir).x + newHead.x
newHead.y = dir_posi(self.dir).y + newHead.y
newHead.x = (newHead.x + grid_col_count) % grid_col_count
newHead.y = (newHead.y + grid_col_count) % grid_col_count
if self.grid[newHead.y * grid_col_count + newHead.x] == 1{
initialize(self)
return
}else if self.grid[newHead.y * grid_col_count + newHead.x] == 2{
self.setGridType(newHead, Body)
self.body = Cons(newHead, self.body)
generate_Food(self)
}else {
self.setGridType(newHead, Body)
self.body = Cons(newHead, self.body)
self.setGridType(get_tail(self.body), Default)
self.body = delete_tail(self.body)
}
}
首先，通过tran_step方法识别外部键盘的响应并对应不同的输入方向指令。
其次，通过step方法来过滤输入方向是否合法。游戏规定蛇无法转向180度，但在蛇身长度为1时，蛇可以上下左右自由移动。
最后，调用go_step方法完成蛇的移动。
fn go_step(self: GameState){
let head : Position = get_head(self.body)
let newHead : Position = {x: head.x , y: head.y }
newHead.x = dir_posi(self.dir).x + newHead.x
newHead.y = dir_posi(self.dir).y + newHead.y
newHead.x = (newHead.x + grid_col_count) % grid_col_count
newHead.y = (newHead.y + grid_col_count) % grid_col_count
if self.grid[newHead.y * grid_col_count + newHead.x] == 1{
initialize(self)
return
}else if self.grid[newHead.y * grid_col_count + newHead.x] == 2{
self.setGridType(newHead, Body)
self.body = Cons(newHead, self.body)
generate_Food(self)
}else {
self.setGridType(newHead, Body)
self.body = Cons(newHead, self.body)
self.setGridType(get_tail(self.body), Default)
self.body = delete_tail(self.body)
}
}
在go_step方法中，首先通过self.dir的Position获得 新头的位置，其次判断新头的位置是普通格子，蛇的身体还是食物。
- 如果为普通格子，则将新头设置为蛇身，删除蛇原本的尾巴
- 如果为蛇的身体，本轮游戏结束，重新initialize整场游戏
- 如果为食物，则吃掉这个食物，并把食物的位置设置成蛇身
通过外部引用画图
声明外部函数引用
type Canvas_ctx
fn set_stroke_color(self : Canvas_ctx, color : Int) = "canvas" "set_stroke_color"
fn set_line_width(self : Canvas_ctx, width : Double) = "canvas" "set_line_width"
fn stroke_rect(self : Canvas_ctx, x : Int, y : Int, width : Int, height : Int) = "canvas" "stroke_rect"
fn fill_rect(self : Canvas_ctx, x : Int, y : Int, width : Int, height : Int) = "canvas" "fill_rect"
fn set_fill_style(self : Canvas_ctx, color : Int) = "canvas" "set_fill_style"
然后进行画图
pub fn draw(canvas : Canvas_ctx, snake : GameState) {
let mut c = 0
// draw backgroud
while c < grid_col_count {
canvas.set_fill_style(0)
canvas.fill_rect(c, 0, 1, grid_row_count)
c = c + 1
}
draw_piece(canvas, snake.grid, (0, 0))
}
pub fn draw_piece(canvas : Canvas_ctx, matrix : Array[Int],
offset : (Int, Int)) {
let mut r = 0
let mut c = 0
let mut c0 = 0
while c < matrix.length() {
if matrix[c] == 0 {
c = c + 1
continue
}
c0 = c % grid_col_count
r = c / grid_col_count
canvas.set_fill_style(matrix[c] + 1)
canvas.fill_rect( offset.0 + c0, r, 1, 1)
canvas.set_stroke_color(1)
canvas.set_line_width(0.1)
canvas.stroke_rect( c0, r, 1, 1)
c = c + 1
}
}
JavaScript 键盘监听与画面更新
window.addEventListener("keydown", (e) => {
if (!requestAnimationFrameId) return
switch (e.key) {
case "ArrowLeft": {
snake_step(snake, 3)
snake_draw(context, snake)
break
}
case "ArrowRight": {
snake_step(snake, 4)
snake_draw(context, snake)
break
}
case "ArrowDown": {
snake_step(snake, 2)
snake_draw(context, snake)
break
}
case "ArrowUp": {
snake_step(snake, 1)
snake_draw(context, snake)
break
}
}
})
update画面，调用snake_step和snake_draw方法
function update(time = 0) {
const deltaTime = time - lastTime
dropCounter += deltaTime
if (dropCounter > dropInterval) {
snake_step(snake, 5);
dropCounter = 0
}
lastTime = time
snake_draw(context, snake)
requestAnimationFrameId = requestAnimationFrame(update)
}