JavaScriptの練習：簡単なアニメ（ボールが動く）
業務系のアプリつくりが目的なんですが、やはりこういうのは避けて通れないみたいです。できたものはこちら。
ボールがあっちこっちに動きます。canvasの端に来ると速度の符号を変えて完全弾性衝突のようになっているところが「ほーお」とうなづけるところでした。
アニメにするには、アニメのループ関数の中に「requestAnimationFrame(loop);」を入れて、loop()を一度、外から呼び出す必要があるようです。
あと、軌跡が残るのは、「ctx.fillStyle = ‘rgba(0, 0, 0, 0.25)’」で、0.25の半透明を指定しており、過去4回分が少しずつ色を薄めつつ残ることになります。うまくできています。
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;
}
HTMLはこちら
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Bouncing balls</title>
<link rel="stylesheet" href="style.css">
</head>
<body>
<h1>bouncing balls</h1>
<canvas></canvas>
<script src="script.js"></script>
</body>
</html>
JavaScriptはこちら。
// setup canvas
var canvas = document.querySelector('canvas');
var ctx = canvas.getContext('2d');
var width = canvas.width = window.innerWidth;
var height = canvas.height = window.innerHeight;
var testBall = new Ball(50, 100, 4, 4, 'blue', 10);
// function to generate random number
function random(min,max) {
var num = Math.floor(Math.random()*(max-min)) + min;
return num;
}
function Ball(x, y, velX, velY, color, size) {
this.x = x;
this.y = y;
this.velX = velX;
this.velY = velY;
this.color = color;
this.size = size;
}
Ball.prototype.draw = function() {
ctx.beginPath();
ctx.fillStyle = this.color;
ctx.arc(this.x, this.y, this.size, 0, 2 * Math.PI);
ctx.fill();
}
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;
}
var balls = [];
function loop() {
ctx.fillStyle = 'rgba(0, 0, 0, 0.25)';
ctx.fillRect(0, 0, width, height);
while (balls.length < 25) {
var size = random(10,20);
var ball = new Ball(
// ball position always drawn at least one ball width
// away from the adge of the canvas, to avoid drawing errors
random(0 + size,width - size),
random(0 + size,height - size),
random(-7,7),
random(-7,7),
'rgb(' + random(0,255) + ',' + random(0,255) + ',' + random(0,255) +')',
size
);
balls.push(ball);
}
for (var i = 0; i < balls.length; i++) {
balls[i].draw();
balls[i].update();
balls[i].collisionDetect();
}
requestAnimationFrame(loop);
}
Ball.prototype.collisionDetect = function() {
for (var j = 0; j < balls.length; j++) {
if (!(this === balls[j])) {
var dx = this.x - balls[j].x;
var dy = this.y - balls[j].y;
var distance = Math.sqrt(dx * dx + dy * dy);
if (distance < this.size + balls[j].size) {
balls[j].color = this.color = 'rgb(' + random(0, 255) + ',' + random(0, 255) + ',' + random(0, 255) +')';
}
}
}
}
loop();
CSSはこちら
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 white;
}