canvas Draw the clock interface and use the timer to redraw the entire canvas regularly to achieve the effect of simulating a dynamic clock.
The difficulty lies in:
The wrapping of the scale is not difficult to calculate, but the wrapping of the text is more tricky. The text drawn by the canvas is above the drawing coordinates (the text baseline and alignment), the offset needs to be calculated so that the midpoint of the text falls exactly on the circle.
This step is quite painless, because there is no way to measure the character height in the API, and using fontSize is not actually the exact height of the character. Therefore, the y coordinate is offset downward by half the line height, making it Vertically centered, but always not accurate enough. The x coordinate of half the line width is offset to the left so that it is horizontally centered. There is no such problem because the API provides a method for measuring the line width.
Everything happens because ctx.measureText(text).width exists, but ctx.measureText(numText).height does not exist. Printing measurement results also has only one width attribute. The document says that canvas's support for drawing text is relatively weak. From this point of view, it is more than weak.
Directly setting the baseline and alignment to center seems to have a certain error, and it doesn’t always look so pleasing to the eye. Both methods are written in the code below.
Walking clock preview:
The time display may have slight errors.
Knowledge points and solution reference diagrams
The main knowledge points are the coordinate formula of a circle, and the calculation of trigonometric functions sin and cos. In fact, the coordinate formula of a circle is not used much, and introducing the evaluation may complicate it.
The following picture is a reference picture for calculating tick coordinates and whole point text drawing coordinates:
Canvas drawing clock effect code writing
The following is the entire code:
<!DOCTYPE html><html lang="en"><head>
<meta charset="UTF-8">
<meta name="viewport" content="width=1024, height=768,initial-scale=1.0,maximum-scale=1.0,user-scalable=0">
<title>时钟</title></head><body><p style="margin: 50px">
<canvas width="300" height="300"></canvas>
<canvas width="200" height="200" style="background-color: #bbbbbb"></canvas>
<canvas width="200" height="200"></canvas>
<canvas width="200" height="200"></canvas></p><script>
var clockHelper = function (canvas, config) {
if (!config) {
config = {}
} var ctx = canvas.getContext('2d'); var deColor = config.deColor ? config.deColor : '#333333'; var deConfig = {
ringWidth: config.ringWidth ? config.ringWidth : 6,//圆环宽度
ringColor: config.ringColor ? config.ringColor : deColor,//圆环颜色
hSaleL: config.hSaleL ? config.hSaleL : 8,//时刻度线长
hScaleWidth: config.hScaleWidth ? config.hScaleWidth : 4,//时刻度线宽
hScaleColor: config.hScaleColor ? config.hScaleColor : deColor,//时刻度颜色
msSaleL: config.msSaleL ? config.msSaleL : 4,//分秒刻度线长
msScaleWidth: config.msScaleWidth ? config.msScaleWidth : 2,//分秒刻度线宽
msScaleColor: deColor,//分秒刻度颜色
hFontSize: config.hFontSize ? config.hFontSize : 18,//整点文字大小
hHandWidth: config.hHandWidth ? config.hHandWidth : 10,//时针宽度
mHandWidth: config.mHandWidth ? config.mHandWidth : 5,//分针宽度
sHandWidth: config.sHandWidth ? config.sHandWidth : 2,//秒针宽度
hHandColor: config.hHandColor ? config.hHandColor : deColor,//时针颜色
mHandColor: config.mHandColor ? config.mHandColor : deColor,//分针颜色
sHandColor: config.sHandColor ? config.sHandColor : '#bb3333',//秒针颜色
handMode: ['ms', 's'].indexOf("" + config.handMode) !== -1 ? config.handMode : 's',//指针读秒模式，ms:毫秒，s：秒。
clockFaceColor: config.clockFaceColor ? config.clockFaceColor : '',
}; var ox = canvas.width / 2; var oy = canvas.height / 2; var width = canvas.width; var height = canvas.height;
ctx.font = deConfig.hFontSize + "px 黑体"; //中线圆环半径
var ringR = (width < height) ? (width / 2 - deConfig.ringWidth / 2) : (height / 2 - deConfig.ringWidth / 2); //内圆环半径
var ringInnerR = (width < height) ? (width / 2 - deConfig.ringWidth) : (height / 2 - deConfig.ringWidth); var timer; var timeSleep = 100; var isStart = false; function start() {
if (isStart) { return;
}
isStart = true; if (deConfig.handMode == 'ms') {
timeSleep = 100;
} else {
timeSleep = 1000;
}
ctx.clearRect(0, 0, width, height);
draw();
timer = setInterval(function () {
if (isStart) {
ctx.clearRect(0, 0, width, height);
draw();
}
}, timeSleep);
} function stop() {
isStart = false;
clearInterval(timer)
} function draw() {
beforeDraw();
drawCircleFace();
drawHands();
afterDraw();
} function drawCircleFace() {
ctx.fillStyle = deConfig.ringColor;
ctx.strokeStyle = deConfig.ringColor;
ctx.lineWidth = deConfig.ringWidth;
ctx.beginPath();
ctx.arc(ox, oy, ringR, 0, Math.PI * 2);
ctx.stroke(); if (deConfig.clockFaceColor) {
ctx.fillStyle = deConfig.clockFaceColor;
ctx.fill();
} var x1 = ox; var y1 = oy; var x2 = ox; var y2 = oy; var radin = 0;
ctx.lineWidth = deConfig.hScaleWidth; // ctx.beginPath();
for (var i = 1; i <= 60; i++) {
radin = i * 6 * Math.PI / 180;
x1 = ox + ringInnerR * Math.sin(radin);
y1 = oy - ringInnerR * Math.cos(radin); if (i % 5 === 0) {
ctx.lineWidth = deConfig.hScaleWidth;
x2 = ox + (ringInnerR - deConfig.hSaleL) * Math.sin(radin);
y2 = oy - (ringInnerR - deConfig.hSaleL) * Math.cos(radin);
ctx.fillStyle = deConfig.hScaleColor; var numText = i / 5 + ""; var textWidth = ctx.measureText(numText).width; var x3 = ox + (ringInnerR - deConfig.hSaleL - deConfig.hFontSize) * Math.sin(radin); var y3 = oy - (ringInnerR - deConfig.hSaleL - deConfig.hFontSize) * Math.cos(radin);
ctx.textAlign = 'center';
ctx.textBaseline = 'middle'; //不设置文字居中，基线居中，自己计算。貌似都有误差。因为旋转过程中，角度变化，且文字宽高不尽相同
// var x3 = ox + (ringInnerR - deConfig.hSaleL - deConfig.hFontSize) * Math.sin(radin) - textWidth / 2;
// var y3 = oy - (ringInnerR - deConfig.hSaleL - deConfig.hFontSize) * Math.cos(radin) + deConfig.hFontSize/ 2;
//x2，y2已经求过，化简为：
// var x3 = x2 - deConfig.hFontSize * Math.sin(radin) - textWidth / 2;
// var y3 = y2 + deConfig.hFontSize * Math.cos(radin) + textWidth / 2;
//文字x轴向左偏移一半文字宽，使之水平居中;向下偏移一半高度,使之垂直居中。
// 实际中发现，字高没法测（api无），而使用fontSize不准。但y轴加上字宽，位置倒是更对齐一些。
// var x3 = x2 + textWidth / 2;
// var y3 = y2 - deConfig.hFontSize / 2;
ctx.fillText(numText, x3, y3);
} else {
ctx.lineWidth = deConfig.msScaleWidth;
x2 = ox + (ringInnerR - deConfig.msSaleL) * Math.sin(radin);
y2 = oy - (ringInnerR - deConfig.msSaleL) * Math.cos(radin);
}
ctx.beginPath();
ctx.moveTo(x1, y1);
ctx.lineTo(x2, y2);
ctx.stroke();
}
} //改变坐标中点，并旋转画布也许是更好的选择。
function drawHands() {
var date = new Date(); var h = date.getHours() % 12; var m = date.getMinutes(); var s = date.getSeconds(); var ms = date.getMilliseconds(); // console.log(h + "：" + m + "：" + s);
// 时针
var hRadin = (h + m / 60 + s / 3600) * Math.PI * 2 / 12; var mRadin = (m + s / 60) * Math.PI * 2 / 60; var sRadin; if (deConfig.handMode == 'ms') {
sRadin = (s + ms / 1000) * Math.PI * 2 / 60;
} else {
sRadin = s * Math.PI * 2 / 60;
} var x = 0; var y = 0; var hDotR = deConfig.hHandWidth + 2; var mDotR = 0.6 * hDotR var sDotR = 0.5 * hDotR //秒针半径
var sHandR = ringInnerR - deConfig.hSaleL * 2
//分针半径
var mHandR = 0.8 * sHandR; //时针半径
var hHandR = 0.7 * mHandR; //时针
ctx.beginPath();
ctx.lineWidth = deConfig.hHandWidth;
ctx.strokeStyle = deConfig.hHandColor;
ctx.strokeStyle = deConfig.hHandColor;
ctx.moveTo(ox, oy);
x = ox + hHandR * Math.cos(hRadin - Math.PI / 2);
y = oy + hHandR * Math.sin(hRadin - Math.PI / 2);
ctx.lineTo(x, y);
ctx.stroke(); //针尖。直接圆型了（矩形指针来绘制针尖，计算复杂。。。）
ctx.beginPath();
ctx.lineWidth = 0;
ctx.arc(x, y, deConfig.hHandWidth / 2, 0, 2 * Math.PI);
ctx.fill(); //中心
ctx.beginPath(); // ctx.lineWidth = hDotR;
ctx.arc(ox, oy, hDotR / 2, 0, Math.PI * 2);
ctx.fill();
ctx.stroke(); //分针
ctx.beginPath();
ctx.lineWidth = deConfig.mHandWidth;
ctx.strokeStyle = deConfig.mHandColor;
ctx.fillStyle = deConfig.mHandColor;
ctx.moveTo(ox, oy);
x = ox + mHandR * Math.cos(mRadin - Math.PI / 2);
y = oy + mHandR * Math.sin(mRadin - Math.PI / 2);
ctx.lineTo(x, y);
ctx.stroke(); //针尖。直接圆型了（矩形指针来绘制针尖，计算复杂。。。）
ctx.beginPath();
ctx.lineWidth = 0;
ctx.arc(x, y, deConfig.mHandWidth / 2, 0, 2 * Math.PI);
ctx.fill(); //中心
ctx.beginPath();
ctx.arc(ox, oy, mDotR / 2, 0, Math.PI * 2);
ctx.stroke(); //秒针
ctx.beginPath();
ctx.strokeStyle = deConfig.sHandColor;
ctx.fillStyle = deConfig.sHandColor;
ctx.lineWidth = deConfig.sHandWidth; //秒针有长短两线
x = ox - sHandR / 4 * Math.cos(sRadin - Math.PI / 2);
y = oy - sHandR / 4 * Math.sin(sRadin - Math.PI / 2);
ctx.moveTo(x, y);
x = ox + sHandR * Math.cos(sRadin - Math.PI / 2);
y = oy + sHandR * Math.sin(sRadin - Math.PI / 2);
ctx.lineTo(x, y);
ctx.stroke(); //针尖。直接圆型了（矩形指针来绘制针尖，计算复杂。。。）
ctx.beginPath();
ctx.lineWidth = 0;
ctx.arc(x, y, deConfig.sHandWidth / 2, 0, 2 * Math.PI);
ctx.fill(); //中心
ctx.beginPath();
ctx.fillStyle = deColor;
ctx.arc(ox, oy, sDotR, 0, Math.PI * 2);
ctx.fill();
ctx.stroke();
} function beforeDraw() {
if (typeof exp.beforeDraw === 'function') {
exp.beforeDraw(ctx, deConfig);
}
} function afterDraw() {
if (typeof exp.afterDraw === 'function') {
exp.afterDraw(ctx, deConfig);
}
} var exp = {
start: start,
stop: stop,
beforeDraw: null,
afterDraw: null,
} return exp;
} var clockCanvas1 = document.getElementsByTagName('canvas')[0]; var clockCanvas2 = document.getElementsByTagName('canvas')[1]; var clockCanvas3 = document.getElementsByTagName('canvas')[2]; var clockCanvas4 = document.getElementsByTagName('canvas')[3]; var clock = clockHelper(clockCanvas1, {mHandColor: '#3333bb', sHandColor: '#bb3333'});
clock.start();
setTimeout(function () {
clock.stop()
}, 5000)
setTimeout(function () {
clock.start();
}, 8000)
clockHelper(clockCanvas2, {
mHandColor: 'green',
hHandWidth: 6,
mHandWidth: 4,
hFontSize: 14,
hScaleWidth: 2,
handMode: 'ms'
}).start();
clockHelper(clockCanvas2, {
mHandColor: 'green',
hHandWidth: 6,
mHandWidth: 4,
hFontSize: 14,
hScaleWidth: 2,
handMode: 'ms'
}).start();
clockHelper(clockCanvas3, {
deColor: '#bbbbbb',
sHandColor: '#bbbbbb',
clockFaceColor: '#112233',//钟面
hHandWidth: 6,
mHandWidth: 4,
hFontSize: 14,
hScaleWidth: 2,
handMode: 's'
}).start(); var clock4 = clockHelper(clockCanvas4, {
deColor: '#bbbbbb',
sHandColor: '#bbbbbb', // clockFaceColor: '#112233',
hHandWidth: 6,
mHandWidth: 4,
hFontSize: 14,
hScaleWidth: 2,
handMode: 's'
});
clock4.afterDraw = function (ctx, deConfig) {
var grd = ctx.createLinearGradient(0, 0, clockCanvas4.width, clockCanvas4.height);
grd.addColorStop(0, "rgba(255,0,0,0.3)");
grd.addColorStop(1, "rgba(0,0,255,0.5)");
ctx.fillStyle = grd;
ctx.arc(clockCanvas4.width/2,clockCanvas4.height/2,clockCanvas4.width/2,0,Math.PI*2); // ctx.fillRect(0, 0, clockCanvas4.width, clockCanvas4.height);
ctx.fill();
ctx.fillText('时钟绘制完成后，自定义其他绘制',clockCanvas4.width/2,clockCanvas4.height - deConfig.hFontSize);
};
clock4.start();</script></body></html>Copy after login
Instructions:
1. The first parameter of clockHelper is passed into the canvas. The second parameter is passed into the configuration object of the clock interface, including the color and size of the pointer and scale, etc. The configuration items are relative to the deConfig default object in clockHelper. You can pass in the parameters by referring to the properties of deConfig.
2. The encapsulation of clockHelper is slightly poor, and it is only basically usable. But there aren’t many attributes, so it shouldn’t be difficult to transform.
3. Provides methods before and after drawing the clock interface. You can execute your own logic in the two methods beforeDraw and afterDraw. However, since the pre-design did not leave enough blank pixels, it is of little use. Only some simple repainting can be done. For example, add colors and gradients to the clock face.
Related recommendations:
H5 C3 to achieve clock effect
How to use Canvas to create clock animation
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