本文實例講述了JavaScript+html5 canvas繪制時鐘效果。分享給大家供大家參考，具體如下：
HTML部分：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0,minimum-scale=1.0,maximum-scale=1.0">
<title>canvas繪圖</title>
</head>
<body onload="init()">
<canvas id="canvas" width="200px" height="200px"></canvas>
</body>
</html>
JavaScript部分：
function init(){
var canvas = document.getElementById("canvas"),
context = canvas.getContext("2d");
setInterval(function(){draw(canvas, context)},1000);
}
function draw(canvas, context){
var x = canvas.width,
y = canvas.height,
r = Math.min(x/2, y/2);
context.clearRect(0, 0, x, y); //清除繪畫歷史
//繪畫鐘框
context.fillStyle = "#f1f1f1";
drawCircle(context, x, y, r);
//繪畫文字
var tx = x/2,ty = y/2,tr = 0.8*r;
context.font = "bold 12px 微軟雅黑";
context.fillStyle = "#000";
drawText(context, "1", tx + 0.5*tr,ty - 0.866*tr);
drawText(context, "2", tx + 0.866*tr, ty - 0.5*tr);
drawText(context, "3", tx + tr, ty);
drawText(context, "4", tx + 0.866*tr, ty + 0.5*tr);
drawText(context, "5", tx + 0.5*tr, ty + 0.866*tr);
drawText(context, "6", tx, ty + tr);
drawText(context, "7", tx - 0.5*tr, ty + 0.866*tr);
drawText(context, "8", tx - 0.866*tr, ty + 0.5*tr);
drawText(context, "9", tx - tr, ty);
drawText(context, "10", tx - 0.866*tr, ty - 0.5*tr);
drawText(context, "11", tx - 0.5*tr, ty - 0.866*tr);
drawText(context, "12", tx, ty - tr);
//獲取當前時間
var date = new Date(),
h = date.getHours(),
m = date.getMinutes(),
s = date.getSeconds(),
angleH = (360/12)*Math.PI/180,
angleM = (360/60)*Math.PI/180
context.strokeSyle = "#000";
//繪制時刻度
drawScale(context, x, y, r, angleH, -0.88*r, -0.96*r, 3);
//繪制分刻度
drawScale(context, x, y, r, angleM, -0.93*r, -0.96*r, 1);
//繪畫時分秒針
drawCircle(context, x, y, 3);
drawNeedle(context, x, y, r, h*angleH + m*angleM/12, -0.5*r);
drawNeedle(context, x, y, r, m*angleM + s*angleM/60, -0.6*r);
drawNeedle(context, x, y, r, s*angleM, -0.75*r);
}
//繪畫圓
function drawCircle(context, x, y, r){
context.save();
context.beginPath();
context.arc(x/2, y/2, r, 0, Math.PI*2, 0);
context.fill();
context.closePath();
context.restore();
}
//繪畫文字方法
function drawText(context, text, x, y){
context.save();
x -= (context.measureText(text).width/2);
y += 4;
context.translate(x, y);
context.fillText(text, 0, 0);
context.restore();
}
//繪制刻度方法
function drawScale(context, x, y, r, rotate, start, end, lineWidth){
context.save();
context.beginPath();
context.translate(x/2,y/2);
context.lineWidth = lineWidth;
for (var i = 0; i < 60; i++) {
context.rotate(rotate);
context.moveTo(0, start);
context.lineTo(0, end);
}
context.closePath();
context.stroke();
context.restore();
}
//繪畫時分秒針方法
function drawNeedle(context, x, y, r, rotate, line){
context.save();
context.translate(x/2,y/2);
context.beginPath();
context.rotate(rotate);
context.moveTo(0, 0.1*r);
context.lineTo(0, line);
context.closePath();
context.stroke();
context.restore();
}
希望本文所述對大家JavaScript程序設計有所幫助。