游戏障碍

按下按钮可移动红色方块:

添加一些障碍

现在我们想为游戏添加一些障碍。

将新组件添加到游戏区域。将其设为绿色,宽 10 像素,高 200 像素,然后将其放置在右侧 300 像素、向下 120 像素的位置。

还要更新每一帧中的障碍物组件:

实例

var myGamePiece;
var myObstacle;
function startGame() {
 myGamePiece = new component(30, 30, "red", 10, 120);
 myObstacle = new component(10, 200, "green", 300, 120);
 myGameArea.start();
}
function updateGameArea() {
 myGameArea.clear();
 myObstacle.update();
 myGamePiece.newPos();
 myGamePiece.update();
}

亲自试一试

撞到障碍 = 游戏结束

在上面的例子中,当您碰到障碍物时什么也不会发生。在游戏中,这并不令人满意。

我们如何知道我们的红色方块是否撞到了障碍物?

在组件构造函数中创建一个新方法,用于检查该组件是否与另一个组件相撞。每次帧更新时都应调用此方法,每秒 50 次。

还要向 myGameArea 对象添加 stop() 方法,该方法会清除 20 毫秒的间隔。

实例

var myGameArea = {
 canvas : document.createElement("canvas"),
 start : function() {
 this.canvas.width = 480;
 this.canvas.height = 270;
 this.context = this.canvas.getContext("2d");
 document.body.insertBefore(this.canvas, document.body.childNodes[0]);
 this.interval = setInterval(updateGameArea, 20);
 },
 clear : function() {
 this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
 },
 stop : function() {
 clearInterval(this.interval);
 }
}
function component(width, height, color, x, y) {
 this.width = width;
 this.height = height;
 this.speedX = 0;
 this.speedY = 0;
 this.x = x;
 this.y = y;
 this.update = function() {
 ctx = myGameArea.context;
 ctx.fillStyle = color;
 ctx.fillRect(this.x, this.y, this.width, this.height);
 }
 this.newPos = function() {
 this.x += this.speedX;
 this.y += this.speedY;
 }
 this.crashWith = function(otherobj) {
 var myleft = this.x;
 var myright = this.x + (this.width);
 var mytop = this.y;
 var mybottom = this.y + (this.height);
 var otherleft = otherobj.x;
 var otherright = otherobj.x + (otherobj.width);
 var othertop = otherobj.y;
 var otherbottom = otherobj.y + (otherobj.height);
 var crash = true;
 if ((mybottom < othertop) ||
 (mytop > otherbottom) ||
 (myright < otherleft) ||
 (myleft > otherright)) {
 crash = false;
 }
 return crash;
 }
}
function updateGameArea() {
 if (myGamePiece.crashWith(myObstacle)) {
 myGameArea.stop();
 } else {
 myGameArea.clear();
 myObstacle.update();
 myGamePiece.newPos();
 myGamePiece.update();
 }
}

亲自试一试

移动障碍物

障碍物在静止时没有危险,因此我们希望它动起来。

每次更新时更改 myObstacle.x 的属性值:

实例

function updateGameArea() {
 if (myGamePiece.crashWith(myObstacle)) {
 myGameArea.stop();
 } else {
 myGameArea.clear();
 myObstacle.x += -1;
 myObstacle.update();
 myGamePiece.newPos();
 myGamePiece.update();
 }
}

亲自试一试

多重障碍

添加多个障碍怎么样?

为此,我们需要一个用于计算帧数的属性,以及一个以给定帧速率执行某些操作的方法。

实例

var myGameArea = {
 canvas : document.createElement("canvas"),
 start : function() {
 this.canvas.width = 480;
 this.canvas.height = 270;
 this.context = this.canvas.getContext("2d");
 document.body.insertBefore(this.canvas, document.body.childNodes[0]);
 this.frameNo = 0;
 this.interval = setInterval(updateGameArea, 20);
 },
 clear : function() {
 this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
 },
 stop : function() {
 clearInterval(this.interval);
 }
}
function everyinterval(n) {
 if ((myGameArea.frameNo / n) % 1 == 0) {return true;}
 return false;
}

如果当前帧编号与给定间隔相对应,则 everyinterval 函数返回 true。

首先,如需定义多个障碍物,将障碍物变量声明为数组。

其次,我们需要对 updateGameArea 函数做一些更改。

实例

var myGamePiece;
var myObstacles = [];
function updateGameArea() {
 var x, y;
 for (i = 0; i < myObstacles.length; i += 1) {
 if (myGamePiece.crashWith(myObstacles[i])) {
 myGameArea.stop();
 return;
 }
 }
 myGameArea.clear();
 myGameArea.frameNo += 1;
 if (myGameArea.frameNo == 1 || everyinterval(150)) {
 x = myGameArea.canvas.width;
 y = myGameArea.canvas.height - 200
 myObstacles.push(new component(10, 200, "green", x, y));
 }
 for (i = 0; i < myObstacles.length; i += 1) {
 myObstacles[i].x += -1;
 myObstacles[i].update();
 }
 myGamePiece.newPos();
 myGamePiece.update();
}

亲自试一试

在 updateGameArea 函数中,我们必须循环遍历每个障碍物来查看是否发生碰撞。如果发生碰撞,updateGameArea 函数将停止,并且不再进行绘制。

updateGameArea 函数对帧进行计数,并每隔 150 帧添加一个障碍物。

随机大小的障碍

为了增添游戏的难度和趣味,我们将发送随机大小的障碍物,以便红色方块必须上下移动才不会发生碰撞。

实例

function updateGameArea() {
 var x, height, gap, minHeight, maxHeight, minGap, maxGap;
 for (i = 0; i < myObstacles.length; i += 1) {
 if (myGamePiece.crashWith(myObstacles[i])) {
 myGameArea.stop();
 return;
 }
 }
 myGameArea.clear();
 myGameArea.frameNo += 1;
 if (myGameArea.frameNo == 1 || everyinterval(150)) {
 x = myGameArea.canvas.width;
 minHeight = 20;
 maxHeight = 200;
 height = Math.floor(Math.random()*(maxHeight-minHeight+1)+minHeight);
 minGap = 50;
 maxGap = 200;
 gap = Math.floor(Math.random()*(maxGap-minGap+1)+minGap);
 myObstacles.push(new component(10, height, "green", x, 0));
 myObstacles.push(new component(10, x - height - gap, "green", x, height + gap));
 }
 for (i = 0; i < myObstacles.length; i += 1) {
 myObstacles[i].x += -1;
 myObstacles[i].update();
 }
 myGamePiece.newPos();
 myGamePiece.update();
}

亲自试一试