本文实例讲述了JavaScript+html5 canvas绘制时钟效果。分享给大家供大家参考，具体如下：
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绘图</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); //清除绘画历史
//绘画钟框
context.fillStyle = "#f1f1f1";
drawCircle(context, x, y, r);
//绘画文字
var tx = x/2,ty = y/2,tr = 0.8*r;
context.font = "bold 12px 微软雅黑";
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);
//获取当前时间
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";
//绘制时刻度
drawScale(context, x, y, r, angleH, -0.88*r, -0.96*r, 3);
//绘制分刻度
drawScale(context, x, y, r, angleM, -0.93*r, -0.96*r, 1);
//绘画时分秒针
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);
}
//绘画圆
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();
}
//绘画文字方法
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();
}
//绘制刻度方法
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();
}
//绘画时分秒针方法
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();
}
希望本文所述对大家JavaScript程序设计有所帮助。