导语：距离上一次写canvas，已经过去两年半，如今业务需要，再次拾起，随手记录。
【思考】 时钟的绘制主要在于圆的绘制：1. 使用context.arc()方法直接绘制圆或圆弧； 2. 使用圆的方程（x = r * cosA + X, y = r * sinA + Y）进行描点绘制。指针运行速率较慢，故使用setInterval进行刷新重绘。
【优化】可以使用两个canvas，一个用来绘制表盘，另一个绘制指针，如此，只需刷新重绘指针canvas，表盘canvas保持不变。
<!DOCTYPE html>
<html>
<head>
<title>Canvas Clock</title>
</head>
<body>
<canvas id="clock">Your borswer does not support canvas element.</canvas>
<script type="text/javascript">
/**
* 圆的方程：x = r * cosA + X, y = r * sinA + Y
* 浏览器为了达到抗锯齿的效果会做额外的运算，故为提高渲染效率，均使用整数进行绘制。
*/
(function() {
let clockCvs = document.getElementById('clock')
if (!clockCvs || !clockCvs.getContext) return
clockCvs.width = 310
clockCvs.height = 310
let clockCtx = clockCvs.getContext('2d')
// X坐标偏移
const X = 155
// Y坐标偏移
const Y = 155
// 钟的半径
const R = 150 start()
setInterval(start, 1000) function start () {
clockCtx.clearRect(0, 0, clockCvs.width, clockCvs.height)
renderClockPlate()
renderClockTime()
renderClockHand()
} // 渲染表盘
function renderClockPlate () {
drawCircle(X, Y, '#070702', R, 1)
drawCircle(X, Y, '#4f4f52', R - 3, 5)
drawCircle(X, Y, '#070702', R - 6, 3)
drawCircle(X, Y, '#dddddd', R - 8)
drawCircle(X, Y, '#121213', R - 10, 3)
drawCircle(X, Y, '#19191a', R - 12, 0, 'fill', true) drawCircle(X, Y, '#4e4738', 15, 0, 'fill')
drawCircle(X, Y, '#eac55a', 10, 0, 'fill')
drawCircle(X, Y, '#3e3e41', 8, 0, 'fill')
drawCircle(X, Y, '#000000', 3, 0, 'fill')
} // 渲染时间
function renderClockTime () {
for (let angle = -90; angle < 270; angle = angle + 6) {
let x = Math.round((R - 18) * Math.cos(angle / 180 * Math.PI) + X)
let y = Math.round((R - 18) * Math.sin(angle / 180 * Math.PI) + Y)
let r = angle % 90 === 0 ? 4 : 2
drawCircle(x, y, '#eac55a', r, 0, 'fill')
if (angle % 30 === 0) {
x = Math.round((R - 35) * Math.cos(angle / 180 * Math.PI) + X - 4)
y = Math.round((R - 35) * Math.sin(angle / 180 * Math.PI) + Y + 6)
clockCtx.font = angle % 90 === 0 ? 'bold 15px yahei' : '12px yahei'
clockCtx.fillText((angle + 90) / 30 || 12, x , y)
}
}
} // 渲染表针
function renderClockHand () {
let date = new Date()
let hour = date.getHours()
let minute = date.getMinutes()
let second = date.getSeconds()
// 秒针
let angle1 = (second * 6 - 90)
let x = Math.round((R - 45) * Math.cos(angle1 / 180 * Math.PI) + X)
let y = Math.round((R - 45) * Math.sin(angle1 / 180 * Math.PI) + Y)
drawLine([[X, Y], [x, y]], 1)
// 分针
let angle2 = (minute * 6 - 90)
x = Math.round((R - 65) * Math.cos(angle2 / 180 * Math.PI) + X)
y = Math.round((R - 65) * Math.sin(angle2 / 180 * Math.PI) + Y)
drawLine([[X, Y], [x, y]], 2)
// 时针， 时针角度 = 小时角度 + 分钟角度
let angle3 = ((hour % 12) * 30 - 90) + (angle2 / 12)
x = Math.round((R - 90) * Math.cos(angle3 / 180 * Math.PI) + X)
y = Math.round((R - 90) * Math.sin(angle3 / 180 * Math.PI) + Y)
drawLine([[X, Y], [x, y]], 4) } /**
* @param {String} color 颜色
* @param {Number} r 圆半径
* @param {Number} lineWidth 线条粗细
* @param {String} type 类型，stroke/fill
* @param {Boolean} isLinear 是否渐变
*/
function drawCircle (x, y,color = '#000000', r = 10, lineWidth = 2, type = 'stroke', isLinear = false) {
let grd = clockCtx.createLinearGradient(0, 0, clockCvs.width, clockCvs.height)
grd.addColorStop(0, color)
grd.addColorStop(0.5, '#555555')
grd.addColorStop(1, color)
clockCtx[type + 'Style'] = isLinear ? grd : color
clockCtx.lineWidth = lineWidth
clockCtx.beginPath()
clockCtx.arc(x, y, r, 0, Math.PI * 2, true)
clockCtx.closePath()
clockCtx[type]()
} /**
* @param {Array} pos 坐标点集合，如 [[0, 0], [120, 120]]
* @param {String} color 颜色
* @param {Number} lineWidth 线条粗细
*/
function drawLine (pos, lineWidth = 2, color = '#eac55a') {
clockCtx.strokeStyle = color
clockCtx.lineWidth = lineWidth
clockCtx.beginPath()
clockCtx.moveTo(pos[0][0], pos[0][1])
for (let i = 0, len = pos.length; i < len; i++) {
clockCtx.lineTo(pos[i][0], pos[i][1])
}
clockCtx.stroke()
clockCtx.closePath()
}
})()
</script>
</body>
</html>
优化前
<!DOCTYPE html>
<html>
<head>
<title>Canvas Clock</title>
</head>
<body>
<canvas id="clock" style="position: absolute;">Your borswer does not support canvas element.</canvas>
<canvas id="clockHand" style="position: absolute;">Your borswer does not support canvas element.</canvas>
<script type="text/javascript">
/**
* 圆的方程：x = r * cosA + X, y = r * sinA + Y
* 浏览器为了达到抗锯齿的效果会做额外的运算，故为提高渲染效率，均使用整数进行绘制。
*/
(function() {
let clockCvs = document.getElementById('clock')
let clockHandCvs = document.getElementById('clockHand')
if (!clockCvs || !clockCvs.getContext) return
clockCvs.width = clockHandCvs.width = 310
clockCvs.height = clockHandCvs.height = 310
let clockCtx = clockCvs.getContext('2d')
let clockHandCtx = clockHandCvs.getContext('2d')
// X坐标偏移
const X = 155
// Y坐标偏移
const Y = 155
// 钟的半径
const R = 150 renderClockPlate()
renderClockTime()
renderClockHand()
setInterval(function () {
clockHandCtx.clearRect(0, 0, clockHandCvs.width, clockHandCvs.height)
renderClockHand()
}, 1000) // 渲染表盘
function renderClockPlate () {
drawCircle(clockCtx, clockCvs, X, Y, '#070702', R, 1)
drawCircle(clockCtx, clockCvs, X, Y, '#4f4f52', R - 3, 5)
drawCircle(clockCtx, clockCvs, X, Y, '#070702', R - 6, 3)
drawCircle(clockCtx, clockCvs, X, Y, '#dddddd', R - 8)
drawCircle(clockCtx, clockCvs, X, Y, '#121213', R - 10, 3)
drawCircle(clockCtx, clockCvs, X, Y, '#19191a', R - 12, 0, 'fill', true) drawCircle(clockCtx, clockCvs, X, Y, '#4e4738', 15, 0, 'fill')
drawCircle(clockCtx, clockCvs, X, Y, '#eac55a', 10, 0, 'fill')
drawCircle(clockCtx, clockCvs, X, Y, '#3e3e41', 8, 0, 'fill')
drawCircle(clockCtx, clockCvs, X, Y, '#000000', 3, 0, 'fill')
} // 渲染时间
function renderClockTime () {
for (let angle = -90; angle < 270; angle = angle + 6) {
let x = Math.round((R - 18) * Math.cos(angle / 180 * Math.PI) + X)
let y = Math.round((R - 18) * Math.sin(angle / 180 * Math.PI) + Y)
let r = angle % 90 === 0 ? 4 : 2
drawCircle(clockCtx, clockCvs, x, y, '#eac55a', r, 0, 'fill')
if (angle % 30 === 0) {
x = Math.round((R - 35) * Math.cos(angle / 180 * Math.PI) + X - 4)
y = Math.round((R - 35) * Math.sin(angle / 180 * Math.PI) + Y + 6)
clockCtx.font = angle % 90 === 0 ? 'bold 15px yahei' : '12px yahei'
clockCtx.fillText((angle + 90) / 30 || 12, x , y)
}
}
} // 渲染表针
function renderClockHand () {
let date = new Date()
let hour = date.getHours()
let minute = date.getMinutes()
let second = date.getSeconds()
// 秒针
let angle1 = (second * 6 - 90)
let x = Math.round((R - 45) * Math.cos(angle1 / 180 * Math.PI) + X)
let y = Math.round((R - 45) * Math.sin(angle1 / 180 * Math.PI) + Y)
drawLine(clockHandCtx, [[X, Y], [x, y]], 1)
// 分针
let angle2 = (minute * 6 - 90)
x = Math.round((R - 65) * Math.cos(angle2 / 180 * Math.PI) + X)
y = Math.round((R - 65) * Math.sin(angle2 / 180 * Math.PI) + Y)
drawLine(clockHandCtx, [[X, Y], [x, y]], 2)
// 时针， 时针角度 = 小时角度 + 分钟角度
let angle3 = ((hour % 12) * 30 - 90) + (angle2 / 12)
x = Math.round((R - 90) * Math.cos(angle3 / 180 * Math.PI) + X)
y = Math.round((R - 90) * Math.sin(angle3 / 180 * Math.PI) + Y)
drawLine(clockHandCtx, [[X, Y], [x, y]], 4)
} /**
* @param {String} color 颜色
* @param {Number} r 圆半径
* @param {Number} lineWidth 线条粗细
* @param {String} type 类型，stroke/fill
* @param {Boolean} isLinear 是否渐变
*/
function drawCircle (ctx, cvs, x, y,color = '#000000', r = 10, lineWidth = 2, type = 'stroke', isLinear = false) {
let grd = ctx.createLinearGradient(0, 0, cvs.width, cvs.height)
grd.addColorStop(0, color)
grd.addColorStop(0.5, '#555555')
grd.addColorStop(1, color)
ctx[type + 'Style'] = isLinear ? grd : color
ctx.lineWidth = lineWidth
ctx.beginPath()
ctx.arc(x, y, r, 0, Math.PI * 2, true)
ctx.closePath()
ctx[type]()
} /**
* @param {Array} pos 坐标点集合，如 [[0, 0], [120, 120]]
* @param {String} color 颜色
* @param {Number} lineWidth 线条粗细
*/
function drawLine (ctx, pos, lineWidth = 2, color = '#eac55a') {
ctx.strokeStyle = color
ctx.lineWidth = lineWidth
ctx.beginPath()
ctx.moveTo(pos[0][0], pos[0][1])
for (let i = 0, len = pos.length; i < len; i++) {
ctx.lineTo(pos[i][0], pos[i][1])
}
ctx.stroke()
ctx.closePath()
}
})()
</script>
</body>
</html>