以下是利用JavaScript調用HTML5Canvas畫布所做的效果
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>canvas</title>
<style>body{text-align: center;background:ddd;overflow: hidden;background: #blue;}#canvas{display: inline-block;}</style>
</head>
<body>
<canvas id="canvas"></canvas>
<script>
//定義畫布寬高和生成點的個數
var WIDTH = window.innerWidth, HEIGHT = window.innerHeight, POINT = ;
var canvas = document.getElementById('canvas');
canvas.width = WIDTH,
canvas.height = HEIGHT;
var context = canvas.getContext('2d');
context.strokeStyle = 'rgba(0,0,0,0.02)',
context.strokeWidth = ,
context.fillStyle = 'rgba(255,255,0,0.5)';
var circleArr = [];
//線條：開始xy坐标，結束xy坐标，線條透明度
function Line (x, y, _x, _y, o) {
this.beginX = x,
this.beginY = y,
this.closeX = _x,
this.closeY = _y,
this.o = o;
}
//點：圓心xy坐标，半徑，每幀移動xy的距離
function Circle (x, y, r, moveX, moveY) {
this.x = x,
this.y = y,
this.r = r,
this.moveX = moveX,
this.moveY = moveY;
}
//生成max和min之間的随機數
function num (max, _min) {
var min = arguments[] || ;
return Math.floor(Math.random()*(max-min+)+min);
}
// 繪制原點
function drawCricle (cxt, x, y, r, moveX, moveY) {
var circle = new Circle(x, y, r, moveX, moveY)
cxt.beginPath()
cxt.arc(circle.x, circle.y, circle.r, , *Math.PI)
cxt.closePath()
cxt.fill();
return circle;
}
//繪制線條
function drawLine (cxt, x, y, _x, _y, o) {
var line = new Line(x, y, _x, _y, o)
cxt.beginPath()
cxt.strokeStyle = 'rgba(0,0,0,'+ o +')'
cxt.moveTo(line.beginX, line.beginY)
cxt.lineTo(line.closeX, line.closeY)
cxt.closePath()
cxt.stroke();
}
//初始化生成原點
function init () {
circleArr = [];
for (var i = ; i < POINT; i++) {
circleArr.push(drawCricle(context, num(WIDTH), num(HEIGHT), num(, ), num(, -)/, num(, -)/));
}
draw();
}
//每幀繪制
function draw () {
context.clearRect(,,canvas.width, canvas.height);
for (var i = ; i < POINT; i++) {
drawCricle(context, circleArr[i].x, circleArr[i].y, circleArr[i].r);
}
for (var i = ; i < POINT; i++) {
for (var j = ; j < POINT; j++) {
if (i + j < POINT) {
var A = Math.abs(circleArr[i+j].x - circleArr[i].x),
B = Math.abs(circleArr[i+j].y - circleArr[i].y);
var lineLength = Math.sqrt(A*A + B*B);
var C = /lineLength*-;
var lineOpacity = C > ? : C;
if (lineOpacity > ) {
drawLine(context, circleArr[i].x, circleArr[i].y, circleArr[i+j].x, circleArr[i+j].y, lineOpacity);
}
}
}
}
}
//調用執行
window.onload = function () {
init();
setInterval(function () {
for (var i = ; i < POINT; i++) {
var cir = circleArr[i];
cir.x += cir.moveX;
cir.y += cir.moveY;
if (cir.x > WIDTH) cir.x = ;
else if (cir.x < ) cir.x = WIDTH;
if (cir.y > HEIGHT) cir.y = ;
else if (cir.y < ) cir.y = HEIGHT;
}
draw();
}, );
}
</script>
</body>
</html>
效果如下：
![JavaScript自學筆記【4】函數的聲明與調用目錄二、函數的聲明 三、函數的調用[圖]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)