众所周知,Javascript结合HTML的canvas元素可以开发出丰富多彩的浏览器界面效果,并用于网页游戏的开发,下面分享一个在浏览器上实现的一个多彩弹力球Demo, 在这里有几点需要注意:
1、理解JavaScript类的建立,可参考:点击打开链接。
2、理解JavaScript的原型继承机制,可参考:点击打开链接。
3、理解canvas元素的使用。
我们先来看这个Demo实现的效果:
下面将源代码附上:
1、HTML文档:
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>bouncing - balls</title> <link rel="stylesheet" href="css/ballStyle.css"> </head> <body> <canvas></canvas><!--添加canvas元素--> <script src = "js/colorball.js"></script> </body> </html>
2、js文档,colorball.js
let canvas = document.querySelector('canvas'); let ctx = canvas.getContext('2d'); let width = canvas.width = window.innerWidth;//快速设置变量 let height = canvas.height = window.innerHeight; //返回一个随机数 function random(min, max) { let num = Math.floor(Math.random() * (max - min + 1) + min); return num; } //小球的构造器 function Ball(x, y, velX, velY, color, size) { this.x = x;//最开始的坐标 this.y = y; this.velX = velX;//水平速度 this.velY = velY;//垂直速度 this.color = color;//颜色 this.size = size;//尺寸 } //画出小球 Ball.prototype.draw = function() { ctx.beginPath();//定义画图的开始 ctx.fillStyle = this.color;//定义颜色 ctx.arc(this.x, this.y, this.size, 0, 2 * Math.PI);//arc画圆弧 ctx.fill();//结束绘画 }; //let testBall = new Ball(50, 100, 4, 4, 'blue', 10);//测试 //更新位置 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) >= width) { this.velY = -(this.velY); } if((this.y - this.size) <= 0) { this.velY = -(this.velY); } this.x += this.velX; this.y += this.velY; }; //碰撞检测,当两个小球相撞颜色发生改变 Ball.prototype.collisionDetect = function() { for(let i = 0; i < balls.length; i++) { if(!(this === balls[i])) { let dx = this.x - balls[i].x; let dy = this.y - balls[i].y; let distance = Math.sqrt(dx * dx + dy * dy); if(distance < this.size + balls[i].size) { balls[i].color = this.color = 'rgb(' + random(0, 255) + ',' + random(0, 255) + ',' + random(0, 255) +')'; } } } }; let balls = [];//存储球 //动画 function loop() { ctx.fillStyle = 'rgba(0, 0, 0, 0.25)'; ctx.fillRect(0, 0, width, height); while (balls.length < 200) { let ball = new Ball( random(0, width), random(0, height), random(-8, 7), random(-7, 8), 'rgb(' + random(0,255) + ',' + random(0,255) + ',' + random(0,255) +')', random(10, 20) ); balls.push(ball); } for(let i = 0; i < balls.length; i++) { balls[i].draw(); balls[i].update(); balls[i].collisionDetect(); } requestAnimationFrame(loop); } loop();
3、CSS文档,ballStyle.css
html, body { margin: 0; } html { font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; height: 100%; } body { overflow: hidden; height: inherit; }