弹跳球

很早以前做过一个弹跳球的小游戏。在这个小游戏中很简单的使用了canvas来绘制弹珠。整体看下来是个很简单的小游戏。即游戏中有一个小球可以使用上下左右按键操控左右移动，其余的小球均自由滚动。且顶端记录当前小球的个数。

这个小游戏主要的难点是：canvas

完整代码：

HTML

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>Bouncing balls</title>
    <link rel="stylesheet" href="style.css">
</head>

<body>
    <h1>bouncing balls</h1>
    <p></p>>
    <canvas></canvas>
</body>
</html>

CSS

html, body {
  margin: 0;
}

html {
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  height: 100%;
}

body {
  overflow: hidden;
  height: inherit;
}

h1 {
  font-size: 2rem;
  letter-spacing: -1px;
  position: absolute;
  margin: 0;
  top: -4px;
  right: 5px;
  color: transparent;
  text-shadow: 0 0 4px black;
}

<script type="text/javascript">
    var para = document.querySelector('p');
    var count = 0;

    var canvas = document.querySelector("canvas");
    var ctx = canvas.getContext("2d");

    var width = canvas.width = window.innerWidth;
    var height = canvas.height = window.innerHeight;
    // 定义初始值。
    function random(min, max) {
        var num = Math.floor(Math.random() * (max - min) + min);
        return num;
    }
    // 返回一个随机数。
    function Shape(x, y, velX, velY, exists) {
        this.x = x;
        this.y = y;
        this.velX = velX;
        this.velY = velY;
        this.exists = exists;
    }

    function Ball(x, y, velX, velY, exists, color, size) {
        Shape.call(this, x, y, velY, velX, exists);
        this.color = color;
        this.size = size;
    }
    Ball.prototype = Object.create(Shape.prototype);
    Ball.prototype.constructor = Ball;

    Ball.prototype.draw = function() {
        ctx.beginPath();
        ctx.fillStyle = this.color;
        ctx.arc(this.x, this.y, this.size, 0, 2 * Math.PI);
        ctx.fill();
    }
    // 创建画布。
    Ball.prototype.update = function() {
        if ((this.x + this.size) >= width) {
            this.velX = -(this.velX);
        }
        if ((this.x - this.size) <= 0) {
            this.velX = -(this.velX);
        }
        if ((this.y + this.size) >= height) {
            this.velY = -(this.velY);
        }
        if ((this.y - this.size) <= 0) {
            this.velY = -(this.velY);
        }
        this.x += this.velX;
        this.y += this.velY;
    }
    // 更新小球的位置。
    Ball.prototype.collisionDetect = function() {
        for (j = 0; j < balls.length; j++) {
            if (!(this.x === balls[j].x && this.y === balls[j].y && this.velX === balls[j].velX && this.velY === balls[j].velY)) {
                var dx = this.x - balls[j].x;
                var dy = this.y - balls[j].y;
                var sum1 = Math.sqrt(dx * dx + dy * dy);
                if (sum1 < this.size + balls[j].size) {
                    balls[j].color = this.color = 'rgb(' + random(0, 255) + ',' + random(0, 255) + ',' + random(0, 255) + ')';
                }
            }
        }
    };
    // 使小球移动。
    function EvilCircle(x, y, color, size, velX, velY, exists) {
        Shape.call(this, x, y, exists);
        this.color = "black";
        this.size = 20;
        this.velX = 20;
        this.velY = 20;
    }
    // 创建小球。
    EvilCircle.prototype = Object.create(Shape.prototype);
    EvilCircle.prototype.constructor = EvilCircle;

    EvilCircle.prototype.draw = function() {
        ctx.beginPath();
        ctx.lineWidth = 3;
        ctx.strokeStyle = this.color;
        ctx.arc(this.x, this.y, this.size, 0, 2 * Math.PI);
        ctx.stroke();
    }
    EvilCircle.prototype.checkBound = function() {
        if ((this.x + this.size) >= width) {
            this.x -= this.size;
        }
        if ((this.x - this.size) <= 0) {
            this.x += this.size;
        }
        if ((this.y + this.size) >= height) {
            this.y -= this.size;
        }
        if ((this.y - this.size) <= 0) {
            this.y += this.size;
        }
    }
    // 判断恶魔球是否触碰到边界。
    EvilCircle.prototype.setControls = function() {
        var _this = this;
        window.onkeydown = function(e) {
            if (e.keyCode === 65) {
                _this.x -= _this.velX;
            } else if (e.keyCode === 68) {
                _this.x += _this.velX;
            } else if (e.keyCode === 87) {
                _this.y -= _this.velY;
            } else if (e.keyCode === 83) {
                _this.y += _this.velY;
            }
        }
    }
    // 使用wasd按键移动恶魔小球。
    EvilCircle.prototype.collisionDetect = function() {
        for (j = 0; j < balls.length; j++) {
            if (balls[j].exists) {
                var dx = this.x - balls[j].x;
                var dy = this.y - balls[j].y;
                var sum1 = Math.sqrt(dx * dx + dy * dy);
                if (sum1 < this.size + balls[j].size) {
                    balls[j].exists = false;
                    count--;
                    para.textContent = "小球的个数为：" + count;
                }
            }
        }
    };
    // 吃掉小球后计数
    var evil = new EvilCircle(random(0, width), random(0, height), true);
    evil.setControls();

    var balls = [];

    function loop() {
        ctx.fillStyle = "rgba(255,255,255,1)";
        ctx.fillRect(0, 0, width, height);

        while (balls.length < 20) {
            var ball = new Ball(
                random(0, width),
                random(0, height),
                random(-5, 5),
                random(-5, 5),
                true,
                'rgb(' + random(0, 255) + ',' + random(0, 255) + ',' + random(0, 255) + ')',
                random(10, 20)
            );
            balls.push(ball);
            count++;
            para.textContent = "小球的个数为：" + count;
        }
        for (var i = 0; i < balls.length; i++) {
            if (balls[i].exists) {
                balls[i].draw();
                balls[i].update();
                balls[i].collisionDetect();
            }
        }
        evil.draw();
        evil.checkBound();
        evil.collisionDetect();
        requestAnimationFrame(loop);
    }

    loop();
    </script>

转载请注明出处。欢迎各位指出bug呀~~~

Oriel Yan

lazy~

Oriel Yan

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