因为公司的项目需求，需要做一个K线图，可以让交易者清楚的看到某一交易品种在各个时间段内的报价，以及当前的实时报价。

我所考虑的有两个方向，一是类似于Highcharts等插件的实现方式 -- svg，一是HTML5的canvas。

SVG 是一种使用 XML 描述 2D 图形的语言。 Canvas 通过 JavaScript 来绘制 2D 图形。 Canvas 是逐像素进行渲染的。

经过上面的比较不难发现，

SVG

canvas

2. 实现哪些需求

历史报价

实时报价

支持

拖拽

支持鼠标

滚轮

双指

支持鼠标指针

移动

3. 代码实现过程

1. 准备工作

/** * K-line - K线图渲染函数 * Date: 2019.12.18  Author: isnan */const BLOCK_MARGIN = 2; //方块水平间距const START_PRICE_INDEX = open_price; //开始价格在数据组中的位置const END_PRICE_INDEX = close; //结束价格在数据组中的位置const MIN_PRICE_INDEX = low; //最小价格在数据组中的位置const MAX_PRICE_INDEX = high; //最大价格在数据组中的位置const TIME_INDEX = time; //时间在数据组中的位置const LINE_WIDTH = 1; //1px 宽度 (中间线、x轴等)const BOTTOM_SPACE = 40; //底部空间const TOP_SPACE = 20; //顶部空间const RIGHT_SPACE = 60; //右侧空间let _addEventListener, _removeEventListener, prefix = ; //addEventListener 浏览器兼容function RenderKLine (id, /*Optional*/options) {  if (!id) return;  options = options || {};  this.id = id;   //canvas box id  // detect event model  if (window.addEventListener) {    _addEventListener = "addEventListener";    _removeEventListener = "removeEventListener";  } else {    _addEventListener = "attachEvent";    _removeEventListener = "detachEvent"    prefix = "on";  }  // options params  this.sharpness = options.sharpness;  // 清晰度 (正整数 太大可能会卡顿，取决于电脑配置 建议在2～5区间)  this.blockWidth = options.blockWidth; // 方块的宽度 (最小为3,最大49 为了防止中间线出现位置偏差 设定为奇数,若为偶数则向下减1)  this.buyColor = options.buyColor || #F05452;  // color 涨  this.sellColor = options.sellColor || #25C875;  // color 跌  this.fontColor = options.fontColor || #666666;  //文字颜色  this.lineColor = options.lineColor || #DDDDDD;  //参考线颜色  this.digitsPoint = options.digitsPoint || 2; //报价的digits (有几位小数)  this.horizontalCells = options.horizontalCells || 5; //水平方向切割多少格子 (中间虚线数 = 5 - 1)  this.crossLineStatus = options.crossLineStatus || true; //鼠标移动十字线显示状态  //basic params  this.totalWidth = 0;  //总宽度  this.movingRange = 0; //横向移动的距离 取正数值，使用时再加负号  this.minPrice = 9999999;  this.maxPrice = 0; //绘制的所有数据中 最小/最大数据 用来绘制y轴  this.diffPrice = 0;  //最大报价与最小报价的差值  this.perPricePixel = 0; //每一个单位报价占用多少像素  this.centerSpace = 0; //x轴到顶部的距离 绘图区域  this.xDateSpace = 6;  //x轴上的时间绘制间隔多少组  this.fromSpaceNum = 0;  //x轴上的时间绘制从第 (fromSpaceNum%xDateSpace) 组数据开始   this.dataArr = [];  //数据  this.lastDataTimestamp = undefined; //历史报价中第一个时间戳, 用来和实时报价做比较画图  this.buyColorRGB = {r: 0, g: 0, b: 0};  this.sellColorRGB = {r: 0, g: 0, b: 0};    this.processParams();  this.init();}

定义了一些常量和变量，生成一个

构造函数

/** *    sharpness {number} 清晰度 *    buyColor {string} color - 涨 *    sellColor {string} color - 跌 *    fontColor {string} 文字颜色 *    lineColor {string} 参考线颜色 *    blockWidth {number} 方块的宽度 *    digitsPoint {number} 报价有几位小数 *    horizontalCells {number} 水平方向切割几个格子 *    crossLineStatus {boolean} 鼠标移动十字线显示状态 */

2. init方法和canvas画布的翻转

RenderKLine.prototype.init = function () {  let cBox = document.getElementById(this.id);  // 创建canvas并获得canvas上下文  this.canvas = document.createElement("canvas");  if (this.canvas && this.canvas.getContext) {    this.ctx = this.canvas.getContext("2d");  }  this.canvas.innerHTML = 您的当前浏览器不支持HTML5 canvas;  cBox.appendChild(this.canvas);  this.actualWidth = cBox.clientWidth;  this.actualHeight = cBox.clientHeight;    this.enlargeCanvas();}// 因为绘制区域超出canvas区域，此方法也用来代替clearRect 清空画布的作用RenderKLine.prototype.enlargeCanvas = function () {  this.canvas.width = this.actualWidth * this.sharpness;  this.canvas.height = this.actualHeight * this.sharpness;  this.canvas.style.height = this.canvas.height / this.sharpness + px;  this.canvas.style.width = this.canvas.width / this.sharpness + px;  this.centerSpace = this.canvas.height - (BOTTOM_SPACE + TOP_SPACE) * this.sharpness;  // 将canvas原点坐标转换到右上角  this.transformOrigin();  // base settings  this.ctx.lineWidth = LINE_WIDTH*this.sharpness;  this.ctx.font = `${12*this.sharpness}px Arial`;  // 还原之前滚动的距离  this.ctx.translate(-this.movingRange * this.sharpness, 0);  // console.log(this.movingRange);}

init方法初始化了一个canvas，enlargeCanvas是一个替代clearRect的方法，其中需要注意的是

transformOrigin

// 切换坐标系走向 (原点在左上角 or 右上角)RenderKLine.prototype.transformOrigin = function () {  this.ctx.translate(this.canvas.width, 0);  this.ctx.scale(-1, 1);}

这里有一点需要注意的是，虽然翻转过来绘制一些矩形，直线没什么问题，但是绘制文本是不行的，绘制文本需要还原回去，不然文字就是翻转过来的状态。如下图所示：

3. 移动、拖拽、滚轮事件

//监听鼠标移动RenderKLine.prototype.addMouseMove = function () {  this.canvas[_addEventListener](prefix+"mousemove", mosueMoveEvent);  this.canvas[_addEventListener](prefix+"mouseleave", e => {    this.event = undefined;    this.enlargeCanvas();    this.updateData();  });  const _this = this;  function mosueMoveEvent (e) {    if (!_this.dataArr.length) return;    _this.event = e || event;    _this.enlargeCanvas();    _this.updateData();  }}//拖拽事件RenderKLine.prototype.addMouseDrag = function () {  let pageX, moveX = 0;  this.canvas[_addEventListener](prefix+mousedown, e => {    e = e || event;    pageX = e.pageX;    this.canvas[_addEventListener](prefix+mousemove, dragMouseMoveEvent);  });  this.canvas[_addEventListener](prefix+mouseup, e => {    this.canvas[_removeEventListener](prefix+mousemove, dragMouseMoveEvent);  });  this.canvas[_addEventListener](prefix+mouseleave, e => {    this.canvas[_removeEventListener](prefix+mousemove, dragMouseMoveEvent);  });    const _this = this;  function dragMouseMoveEvent (e) {    if (!_this.dataArr.length) return;    e = e || event;    moveX = e.pageX - pageX;    pageX = e.pageX;    _this.translateKLine(moveX);    // console.log(moveX);  }}//Mac双指行为 & 鼠标滚轮RenderKLine.prototype.addMouseWheel = function () {  addWheelListener(this.canvas, wheelEvent);  const _this = this;  function wheelEvent (e) {      if (Math.abs(e.deltaX) !== 0 && Math.abs(e.deltaY) !== 0) return; //没有固定方向，忽略      if (e.deltaX < 0) return _this.translateKLine(parseInt(-e.deltaX)); //向右      if (e.deltaX > 0) return _this.translateKLine(parseInt(-e.deltaX)); //向左      if (e.ctrlKey) {        if (e.deltaY > 0) return _this.scaleKLine(-1); //向内        if (e.deltaY < 0) return _this.scaleKLine(1); //向外      } else {        if (e.deltaY > 0) return _this.scaleKLine(1); //向上        if (e.deltaY < 0) return _this.scaleKLine(-1); //向下      }  }}

滚轮事件

鼠标移动事件

this

updateData

function drawCrossLine () {  if (!this.crossLineStatus || !this.event) return;  let cRect = this.canvas.getBoundingClientRect();  //layerX 有兼容性问题，使用clientX  let x = this.canvas.width - (this.event.clientX - cRect.left - this.movingRange) * this.sharpness;  let y = (this.event.clientY - cRect.top) * this.sharpness;  // 在报价范围内画线  if (y < TOP_SPACE*this.sharpness || y > this.canvas.height - BOTTOM_SPACE * this.sharpness) return;  this.drawDash(this.movingRange * this.sharpness, y, this.canvas.width+this.movingRange * this.sharpness, y, #999999);  this.drawDash(x, TOP_SPACE*this.sharpness, x, this.canvas.height - BOTTOM_SPACE*this.sharpness, #999999);  //报价  this.ctx.save();  this.ctx.translate(this.movingRange * this.sharpness, 0);  // 填充文字时需要把canvas的转换还原回来，防止文字翻转变形  let str = (this.maxPrice - (y - TOP_SPACE * this.sharpness) / this.perPricePixel).toFixed(this.digitsPoint);  this.transformOrigin();  this.ctx.translate(this.canvas.width - RIGHT_SPACE * this.sharpness, 0);  this.drawRect(-3*this.sharpness, y-10*this.sharpness, this.ctx.measureText(str).width+6*this.sharpness, 20*this.sharpness, "#ccc");  this.drawText(str, 0, y, RIGHT_SPACE * this.sharpness)  this.ctx.restore();}

拖拽事件

pageX

translateKLine

/** * 缩放图表  * @param {int} scaleTimes 缩放倍数 *  正数为放大，负数为缩小，数值*2 代表蜡烛图width的变化度 *  eg:  2 >> this.blockWidth + 2*2   *      -3 >> this.blockWidth - 3*2 * 为了保证缩放的效果， * 应该以当前可视区域的中心为基准缩放 * 所以缩放前后两边的长度在总长度中所占比例应该一样 * 公式：(oldRange+0.5*canvasWidth)/oldTotalLen = (newRange+0.5*canvasWidth)/newTotalLen * diffRange = newRange - oldRange *           = (oldRange*newTotalLen + 0.5*canvasWidth*newTotalLen - 0.5*canvasWidth*oldTotalLen)/oldTotalLen - oldRange */RenderKLine.prototype.scaleKLine = function (scaleTimes) {  if (!this.dataArr.length) return;  let oldTotalLen = this.totalWidth;  this.blockWidth += scaleTimes*2;  this.processParams();  this.computeTotalWidth();  let newRange = (this.movingRange*this.sharpness*this.totalWidth+this.canvas.width/2*this.totalWidth-this.canvas.width/2*oldTotalLen)/oldTotalLen/this.sharpness;  let diffRange = newRange - this.movingRange;  // console.log(newRange, this.movingRange, diffRange);  this.translateKLine(diffRange);}// 移动图表RenderKLine.prototype.translateKLine = function (range) {  if (!this.dataArr.length) return;  this.movingRange += parseInt(range);  let maxMovingRange =  (this.totalWidth - this.canvas.width) / this.sharpness + this.blockWidth;  if (this.totalWidth <= this.canvas.width || this.movingRange <= 0) {    this.movingRange = 0;  } else if (this.movingRange >= maxMovingRange) {    this.movingRange = maxMovingRange;  }  this.enlargeCanvas();  this.updateData();}

4. 核心方法 updateData

所有的绘制过程都是在这个方法中完成的，这样无论想要什么操作，都可以通过此方法重绘canvas来实现，需要做的只是改变原型上的一些属性而已，比如想要左右移动，只需要把

this.movingRange

updateData

RenderKLine.prototype.updateData = function (isUpdateHistory) {  if (!this.dataArr.length) return;  if (isUpdateHistory) {    this.fromSpaceNum = 0;  }  // console.log(data);  this.computeTotalWidth();  this.computeSpaceY();  this.ctx.save();  // 把原点坐标向下方移动 TOP_SPACE 的距离，开始绘制水平线  this.ctx.translate(0, TOP_SPACE * this.sharpness);  this.drawHorizontalLine();  // 把原点坐标再向左边移动 RIGHT_SPACE 的距离，开始绘制垂直线和蜡烛图  this.ctx.translate(RIGHT_SPACE * this.sharpness, 0);  // 开始绘制蜡烛图  let item, col;  let lineWidth = LINE_WIDTH * this.sharpness,      margin = blockMargin = BLOCK_MARGIN*this.sharpness,      blockWidth = this.blockWidth*this.sharpness;//乘上清晰度系数后的间距、块宽度  let blockHeight, lineHeight, blockYPoint, lineYPoint; //单一方块、单一中间线的高度、y坐标点  let realTime, realTimeYPoint; //实时(最后)报价及y坐标点  for (let i=0; i<this.dataArr.length; i++) {    item = this.dataArr[i];    if (item[START_PRICE_INDEX] > item[END_PRICE_INDEX]) {      //跌了 sell      col = this.sellColor;      blockHeight = (item[START_PRICE_INDEX] - item[END_PRICE_INDEX])*this.perPricePixel;      blockYPoint = (this.maxPrice - item[START_PRICE_INDEX])*this.perPricePixel;    } else {      //涨了 buy      col = this.buyColor;      blockHeight = (item[END_PRICE_INDEX] - item[START_PRICE_INDEX])*this.perPricePixel;      blockYPoint = (this.maxPrice - item[END_PRICE_INDEX])*this.perPricePixel;    }    lineHeight = (item[MAX_PRICE_INDEX] - item[MIN_PRICE_INDEX])*this.perPricePixel;    lineYPoint = (this.maxPrice - item[MAX_PRICE_INDEX])*this.perPricePixel;    // if (i === 0) console.log(lineHeight, blockHeight, lineYPoint, blockYPoint);    lineHeight = lineHeight > 2*this.sharpness ? lineHeight : 2*this.sharpness;    blockHeight = blockHeight > 2*this.sharpness ? blockHeight : 2*this.sharpness;    if (i === 0) {      realTime = item[END_PRICE_INDEX];      realTimeYPoint = blockYPoint + (item[START_PRICE_INDEX] > item[END_PRICE_INDEX] ? blockHeight : 0)    };    // 绘制垂直方向的参考线、以及x轴的日期时间    if (i%this.xDateSpace === (this.fromSpaceNum%this.xDateSpace)) {      this.drawDash(margin+(blockWidth-1*this.sharpness)/2, 0, margin+(blockWidth-1*this.sharpness)/2, this.centerSpace);      this.ctx.save();      // 填充文字时需要把canvas的转换还原回来，防止文字翻转变形      this.transformOrigin();      // 翻转后将原点移回翻转前的位置      this.ctx.translate(this.canvas.width, 0);      this.drawText(processXDate(item[TIME_INDEX], this.dataType), -(margin+(blockWidth-1*this.sharpness)/2), this.centerSpace + 12*this.sharpness, undefined, center, top);            this.ctx.restore();    }    this.drawRect(margin+(blockWidth-1*this.sharpness)/2, lineYPoint, lineWidth, lineHeight, col);    this.drawRect(margin, blockYPoint, blockWidth, blockHeight, col);    margin = margin+blockWidth+blockMargin;  }  //绘制实时报价线、价格  this.drawLine((this.movingRange-RIGHT_SPACE) * this.sharpness, realTimeYPoint, (this.movingRange-RIGHT_SPACE) * this.sharpness + this.canvas.width, realTimeYPoint, #cccccc);  this.ctx.save();  this.ctx.translate(-RIGHT_SPACE * this.sharpness, 0);  this.transformOrigin();  this.drawRect((17-this.movingRange) * this.sharpness, realTimeYPoint - 10 * this.sharpness, this.ctx.measureText(realTime).width+6*this.sharpness, 20*this.sharpness, "#ccc");  this.drawText(realTime, (20-this.movingRange) * this.sharpness, realTimeYPoint);  this.ctx.restore();  //最后绘制y轴上报价，放在最上层  this.ctx.translate(-RIGHT_SPACE * this.sharpness, 0);  this.drawYPrice();  this.ctx.restore();  drawCrossLine.call(this);}

这个方法不难，只是绘制时为了方便计算位置，需要经常变换原点坐标，不要搞错了就好。

还需要注意的是

sharpness

5. 更新历史&实时报价方法

// 实时报价RenderKLine.prototype.updateRealTimeQuote = function (quote) {  if (!quote) return;  pushQuoteInData.call(this, quote);}/** * 历史报价 * @param {Array} data 数据 * @param {int}   type 报价类型  默认 60(1小时) *    (1, 5, 15, 30, 60, 240, 1440, 10080, 43200)      (1分钟 5分钟 15分钟 30分钟 1小时 4小时 日 周 月) */RenderKLine.prototype.updateHistoryQuote = function (data, type = 60) {  if (!data instanceof Array || !data.length) return;  this.dataArr = data;  this.dataType = type;  this.updateData(true);}

6. 调用demo

<div id="myCanvasBox" style="width: 1000px; height: 500px;"></div><script>    let data = [      {        "time": 1576648800,         "open_price": "1476.94",         "high": "1477.44",         "low": "1476.76",         "close": "1476.96"      },       //...    ];    let options = {      sharpness: 3,      blockWidth: 11,      horizontalCells: 10    };    let kLine = new RenderKLine("myCanvasBox", options);    //更新历史报价    kLine.updateHistoryQuote(data);    //模拟实时报价    let realTime = `{      "time": 1575858840,       "open_price": "1476.96",       "high": "1482.12",       "low": "1470.96",       "close": "1476.96"    }`;    setInterval(() => {      let realTimeCopy = JSON.parse(realTime);      realTimeCopy.time = parseInt(new Date().getTime()/1000);      realTimeCopy.close = (1476.96 - (Math.random() * 4 - 2)).toFixed(2);      kLine.updateRealTimeQuote(realTimeCopy);     }, parseInt(Math.random() * 1000 + 500))</script>

7. 效果图

4. 总结

这个功能还没有做完，还有很多其他功能以及一些细节上需要开发，比如贝塞尔曲线的绘制，首次加载的Loading，更多历史报价加载等等。现在只是简单总结一下这次遇到的问题，以及一些收获，等下一阶段完善后再做详细记录。

这是我第一次使用canvas绘制一个完整的项目，整个过程还是很有收获的，我想以后还要尝试其他不同的东西，比如游戏。

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持脚本之家。