canvas绘制流程图

最近在做一个需求，根据数据动态生成以下类似的流程图，需要可以设置每个节点的颜色，每个节点可添加点击移动等相关的事件

代码中有做很多的注释和说明，相关的文档说明链接：https://9eb75i.axshare.com

drawFlowChart.js

//画流程图
//画所有的图形：画图和画对应的箭头
function drawFlowChart(context,canvas,flowdata,initTop, initSpaceH){
  //1、判断是否有需要平均计算x的数据
  flowdata.forEach(function(row){
    if(row.isAverage){
      row.data = calChartX(canvas.width,row.data, row.y);
    }
  });
  //2、先要画完所有的图形
  flowdata.forEach(function(row,rowIndex){
    row.y = row.y ? row.y : ( rowIndex==0 ? initTop + initSpaceH : initTop + initSpaceH*rowIndex);
    row = drawRowChart(context, row);  //画图形
  });
  //3、添加要指向的对象，必须要在画完所有图形之后
  flowdata.forEach(function(row){
    row.data.forEach(function(item){
      if(item.arrowArr && item.arrowArr.length){
        item.arrowArr.forEach(function(mItem){
          mItem = addToObj(mItem,flowdata);
        })
      }
    })
  });
  //4、给所有图形画上对应的画箭头，必须要在前两步完成之后
  flowdata.forEach(function(row,rowIndex){
    row.data.forEach(function(item){
      if(item.arrowArr && item.arrowArr.length){
        drawSingleArrow(context,item);//画箭头
      }
    })
  });
  //5、给所有元素添加点击和悬浮事件
  addMethod(canvas,flowdata)
}
//当一行有n个图形并且需要平均排列时用此方法计算每个图形的x
function calChartX(canvasW,data, dataY){
  var startW = 80;
  var stepW = 120;
  var CondW = 30;
  var count = 0;
  for(var i=0;i<data.length;i++){
    if(data[i].type == 'Step'){
      count += stepW;
    }else if(data[i].type == 'Start' || data[i].type == 'End'){
      count += startW;
    }else if(data[i].type == 'Condition'){
      count += CondW;
    }
  }
  //spaceW 计算一行中每个图形的平均间距
  var spaceW = parseInt((canvasW - count)/(data.length+1));
  //计算坐标x
  var prevDiv = [], curW = 0;
  for(var i=0;i<data.length;i++){
    if(data[i].type == 'Step'){
      prevDiv.push(stepW);
      curW = stepW/2;
    }else if(data[i].type == 'Start' || data[i].type == 'End'){
      prevDiv.push(startW);
      curW = startW/2;
    }else if(data[i].type == 'Condition'){
      prevDiv.push(CondW);
      curW = CondW/2;
    }
    var preLength = 0;
    for(var j=0;j<i;j++){
      preLength += prevDiv[j];
    }
    var x = spaceW*(i+1)+preLength+curW;
    var y = data[i].y;
    data[i]['x'] = x;
    data[i]['y'] = y ? y : dataY;
  }
  return data;
}
//生成每列对应的图形
function drawRowChart(context, row){
  row.data.forEach(function(item,index){
    var s = null;
    item.y =  item.y ? item.y : row.y;
    if(item.type == 'Step'){
      s = new Step(context,item.x,item.y,item);
    }else if(item.type == 'Condition'){
      s = new Condition(context,item.x,item.y,item);
    }else if(item.type == 'End'){
      s = new End(context,item.x,item.y,item);
    }else if(item.type == 'Start'){
      s = new Start(context,item.x,item.y,item);
    }
    item.chartObj = s;
  })
  return row;
}
//绘制单个的图形
function drawSingleChart(context,item){
  var s = '';
  if(item.type == 'Step'){
    s = new Step(context,item.x,item.y,item);
  }else if(item.type == 'Condition'){
    s = new Condition(context,item.x,item.y,item);
  }else if(item.type == 'End'){
    s = new End(context,item.x,item.y,item);
  }else if(item.type == 'Start'){
    s = new Start(context,item.x,item.y,item);
  }
  item.chartObj = s;
  return item;
}
//每个对象的坐标范围
function calRange(obj){
  var newObj = {
    minX:obj.x-obj.w/2,
    maxX:obj.x+obj.w/2,
    minY:obj.y-obj.h/2,
    maxY:obj.y+obj.h/2
  }
  return newObj;
}
//处理每一个箭头需要指向的对象
function addToObj(arrObj,flowData){
  flowData.forEach(function(rows){
    rows.data.forEach(function(item){
      if(item.name == arrObj.to){
        arrObj.to = item.chartObj;
      }
    })

  })
  return arrObj;
}
//话每个图形的箭头指向
function drawSingleArrow(context,data){
  var step1 = data.chartObj;
  if(data.arrowArr && data.arrowArr.length){
    data.arrowArr.forEach(function(item){
      step1[item.arrow](item.to,context);
    })
  }
}
//清除单个图形
function repaintSingleChart(context,item){
  var range  = item.chartObj.range;
  //清除之前画的图形
  context.clearRect(range.minX-1,range.minY-1,item.chartObj.w+2,item.chartObj.h+3);

}
//给所有图形添加事件
function addMethod(canvas,flowData){
  //给所有图形添加点击事件
  canvas.onclick=function(ev){
    var ev = ev || window.event;
    var ua = navigator.userAgent.toLowerCase();
    var isIE = ua.indexOf("compatible") > -1 && ua.indexOf("msie") > -1 && !ua.indexOf("opera") > -1; //IE浏览器
    var isEdge= ua.indexOf("Edge") > -1;
    var isIE11 = ua.toLowerCase().match(/rv:([\d.]+)\) like gecko/);
    var curx = (isIE || isEdge || isIE11) ? ev.offsetX : ev.layerX;
    var cury = (isIE || isEdge || isIE11)  ? ev.offsetY : ev.layerY;
    flowData.forEach(function(row,listIndex){
      row.data.forEach(function(item){
        var range  = item.chartObj.range;
        if(curx>=range.minX && curx<=range.maxX && cury>=range.minY && cury<=range.maxY){
          var clickMethod = null;
          if(row.method && row.method.onclick){ //如果每行定义了事件
            //判断每个元素是否有单独定义事件，如果有，取改元素定义的事件，如果没有取每行定义的事件
            if(item.method && item.method.onclick){
              clickMethod = item.method.onclick
            }else{
              clickMethod = row.method.onclick
            }
          }else{
            if(item.method && item.method.onclick){
              clickMethod = item.method.onclick
            }else{
              clickMethod = null;
            }
          }
          if(clickMethod instanceof Function){
            clickMethod(item);
          }
        }
      })
    });
  };
  var timer = null;
  //给所有图形添加mousemove事件
  canvas.onmousemove=function(ev){
    var ev = ev || window.event;
    var ua = navigator.userAgent.toLowerCase();
    var isIE = ua.indexOf("compatible") > -1 && ua.indexOf("msie") > -1 && !ua.indexOf("opera") > -1; //IE浏览器
    var isEdge= ua.indexOf("Edge") > -1;
    var isIE11 = ua.toLowerCase().match(/rv:([\d.]+)\) like gecko/);
    var curx = (isIE || isEdge || isIE11) ? ev.offsetX : ev.layerX;
    var cury = (isIE || isEdge || isIE11)  ? ev.offsetY : ev.layerY;
    clearTimeout(timer);
    flowData.forEach(function(row,listIndex){
      row.data.forEach(function(item){
        var range  = item.chartObj.range;
        if(curx>=range.minX && curx<=range.maxX && cury>=range.minY && cury<=range.maxY){
          var clickMethod = null;
          if(row.method && row.method.onmousemove){ //如果每行定义了事件
            //判断每个元素是否有单独定义事件，如果有，取改元素定义的事件，如果没有取每行定义的事件
            if(item.method && item.method.onmousemove){
              clickMethod = item.method.onmousemove
            }else{
              clickMethod = row.method.onmousemove
            }
          }else{
            if(item.method && item.method.onmousemove){
              clickMethod = item.method.onmousemove
            }else{
              clickMethod = null;
            }
          }
          if(clickMethod instanceof Function){
            timer = setTimeout(function(){
              clickMethod(item);
            },1000)
          }
        }
      })
    });
  }
  //给所有图形添加mouseleave事件
  canvas.onmouseleave=function(ev){
    var ev = ev || window.event;
    var ua = navigator.userAgent.toLowerCase();
    var isIE = ua.indexOf("compatible") > -1 && ua.indexOf("msie") > -1 && !ua.indexOf("opera") > -1; //IE浏览器
    var isEdge= ua.indexOf("Edge") > -1;
    var isIE11 = ua.toLowerCase().match(/rv:([\d.]+)\) like gecko/);
    var curx = (isIE || isEdge || isIE11) ? ev.offsetX : ev.layerX;
    var cury = (isIE || isEdge || isIE11)  ? ev.offsetY : ev.layerY;
    clearTimeout(timer);
    flowData.forEach(function(row){
      row.data.forEach(function(item){
        var range  = item.chartObj.range;
        if(curx>=range.minX && curx<=range.maxX && cury>=range.minY && cury<=range.maxY){
          var clickMethod = null;
          if(row.method && row.method.onmouseleave){ //如果每行定义了事件
            //判断每个元素是否有单独定义事件，如果有，取改元素定义的事件，如果没有取每行定义的事件
            if(item.method && item.method.onmouseleave){
              clickMethod = item.method.onmouseleave
            }else{
              clickMethod = row.method.onmouseleave
            }
          }else{
            if(item.method && item.method.onmouseleave){
              clickMethod = item.method.onmouseleave
            }else{
              clickMethod = null;
            }
          }
          if(clickMethod instanceof Function){
            clickMethod(item);
          }
        }
      })
    });
  }
}

/////////////////////////////////////////基本画图形start////////////////////////////////////////////////////////
//画圆角矩形
function drawRoundRect(context, x, y, w, h, item, radius) {
  radius = radius || 20;
  context.beginPath();
  context.arc(x + radius, y + radius, radius, Math.PI, Math.PI * 3 / 2);
  context.lineTo(w - radius + x, y);
  context.arc(w - radius + x, radius + y, radius, Math.PI * 3 / 2, Math.PI * 2);
  context.lineTo(w + x, h + y - radius);
  context.arc(w - radius + x, h - radius + y, radius, 0, Math.PI * 1 / 2);
  context.lineTo(radius + x, h +y);
  context.arc(radius + x, h - radius + y, radius, Math.PI * 1 / 2, Math.PI);
  context.closePath();
  context.fillStyle = item.color ? (item.color.bgColor ? item.color.bgColor: 'rgba(91,155,213,0.5)'):'white' ; //背景颜色
  context.fill();
  context.strokeStyle= item.color ? (item.color.borderColor ? item.color.borderColor: '#5B9BD5'):'#5B9BD5' ; //边框颜色
  context.font = 'normal 14px 微软雅黑';
  context.fillStyle = item.color ? (item.color.fontColor ? item.color.fontColor: '#5B9BD5'):'#5B9BD5' ; //文字颜色
  context.textAlign="center";
  context.fillText(item.text, x+w/2, y+h/2+6);
  context.stroke();
}
//画菱形
function drawRhombus(context,x, y, l, h, item) {
  context.beginPath();
  context.moveTo(x, y + h);
  context.lineTo(x - l * 2-40, y);
  context.lineTo(x, y - h);
  context.lineTo(x + l * 2+40, y);
  context.closePath();
  context.strokeStyle= item.color ? (item.color.borderColor ? item.color.borderColor: '#5B9BD5'):'#5B9BD5' ; //边框颜色
  context.fillStyle = item.color ? (item.color.bgColor ? item.color.bgColor: 'rgba(91,155,213,0.5)'):'white' ; //背景颜色
  context.fill();
  context.fillStyle = item.color ? (item.color.fontColor ? item.color.fontColor: '#5B9BD5'):'#5B9BD5' ; //文字颜色
  context.font = 'normal 14px 微软雅黑';
  context.fillText(item.text, x, y+3);
  context.stroke();
}
//计算文本的宽高
function textSize(fontSize,fontFamily,text){
  var span = document.createElement("span");
  var result = {};
  result.width = span.offsetWidth;
  result.height = span.offsetHeight;
  span.style.visibility = "hidden";
  span.style.fontSize = fontSize;
  span.style.fontFamily = fontFamily;
  span.style.display = "inline-block";
  document.body.appendChild(span);
  if(typeof span.textContent != "undefined"){
    span.textContent = text;
  }else{
    span.innerText = text;
  }
  result.width = parseFloat(window.getComputedStyle(span).width) - result.width;
  result.height = parseFloat(window.getComputedStyle(span).height) - result.height;
  return result;
}
//Start 圆角矩形对象
function Start(context,x, y, item, h, w) {
  this.flag = 'start';
  var textStyle = textSize('14px','微软雅黑',item.text);
  w = parseInt(textStyle.width)+30;
  this.h = h || 40;
  this.w = w || 2 * this.h;
  this.x = x;
  this.y = y;
  this.text = item.text;
  this.range = calRange(this);
  drawRoundRect(context,x - this.w / 2, y - this.h / 2, this.w, this.h, item);
}
//End 圆角矩形对象
function End(context, x, y, item, h, w) {
  this.flag = 'end';
  var textStyle = textSize('14px','微软雅黑',item.text);
  w = parseInt(textStyle.width)+30;
  this.h = h || 40;
  this.w = w || 2 * this.h;
  this.x = x;
  this.y = y;
  this.text = item.text;
  this.range = calRange(this);
  drawRoundRect(context, x - this.w / 2, y - this.h / 2, this.w, this.h, item, 20);
}
//Step 矩形对象
function Step(context,x, y, item) {
  this.flag = "step";
  var textStyle = textSize('14px','微软雅黑',item.text);
  var w = parseInt(textStyle.width)+30;
  this.h = 40;
  this.w = w;
  this.x = x;
  this.y = y;
  this.text = item.text;
  this.range = calRange(this);
  context.strokeStyle= item.color ? (item.color.borderColor ? item.color.borderColor: '#5B9BD5'):'#5B9BD5' ; //边框颜色
  context.strokeRect(x - this.w / 2, y - this.h / 2, this.w, this.h);
  context.fillStyle = item.color ? (item.color.bgColor ? item.color.bgColor: 'rgba(91,155,213,0.5)'):'white' ; //背景颜色
  context.fillRect(x - this.w / 2, y - this.h / 2,this.w,this.h);
  context.fillStyle = item.color ? (item.color.fontColor ? item.color.fontColor: '#5B9BD5'):'#5B9BD5' ; //文字颜色
  context.textAlign = 'center';
  context.font = 'normal 14px 微软雅黑';
  if(item.text){context.fillText(item.text,x, y+4);}
}
//Condition 菱形对象
function Condition(context, x, y, item) {
  this.flag = "condition";
  var textStyle = textSize('14px','微软雅黑',item.text);
  var w = parseInt(textStyle.width)/4;
  this.l = w;
  this.h = 40;
  this.w = w;
  this.x = x;
  this.y = y;
  this.text = item.text;
  this.range = calRange(this);
  drawRhombus(context,x, y, this.l,this.h, item);
}

/////////////////////////////////////////基本画图形end////////////////////////////////////////////////////////

////////////////////////////////////////////画箭头/////////////////////////////////////////////////////////////
//箭头从start圆角矩形bottom——>top
Start.prototype.drawBottomToTop = function(obj,context) {
  if(obj.flag == "step") {
    var arrow = new Arrow(this.x, this.y + this.h / 2, obj.x, obj.y - obj.h / 2);
    arrow.drawBottomToTop(context);
  } else if(obj.flag == "condition") {
    var arrow = new Arrow(this.x, this.y + this.h / 2, obj.x, obj.y - obj.l);
    arrow.drawBottomToTop(context);
  }
}

//箭头从step矩形bottom——>right
Step.prototype.drawBottomToRight = function(obj,context) {
  var arrow = null;
  if(obj.flag == "step") {
    arrow = new Arrow(this.x, this.y + this.h / 2, obj.x + obj.w / 2 , obj.y);
  } else if(obj.flag == "condition") {
    arrow = new Arrow(this.x , this.y + this.h / 2, obj.x + obj.l*2+40 , obj.y);
  }else if(obj.flag == "start" || obj.flag == "end"){
    arrow = new Arrow(this.x , this.y + this.h / 2, obj.x + obj.w/2 , obj.y);
  }
  arrow.drawBottomToRight(context);
}
//箭头从step矩形bottom——>left
Step.prototype.drawBottomToLeft = function(obj,context) {
  var arrow = null;
  if(obj.flag == "step") {
    arrow = new Arrow(this.x, this.y + this.h / 2, obj.x - obj.w / 2 , obj.y);
  } else if(obj.flag == "condition") {
    arrow = new Arrow(this.x , this.y + this.h / 2, obj.x - obj.l*2-40 , obj.y);
  }else if(obj.flag == "start" || obj.flag == "end"){
    arrow = new Arrow(this.x , this.y + this.h / 2, obj.x - obj.w/2 , obj.y);
  }
  arrow.drawBottomToRight(context);
}
//箭头从step矩形bottom——>top
Step.prototype.drawBottomToTop = function(obj,context) {
  if(obj.flag == "step") {
    var arrow = new Arrow(this.x, this.y + this.h / 2, obj.x, obj.y - obj.h / 2);
    arrow.drawBottomToTop(context);
  } else if(obj.flag == "condition") {
    var arrow = new Arrow(this.x, this.y + this.h / 2, obj.x, obj.y - obj.h);
    arrow.drawBottomToTop(context);
  }
}
//箭头从step矩形right——>left
Step.prototype.drawRightToLeft = function(obj,context) {
  var arrow = null;
  if(obj.flag == "step") {
    arrow = new Arrow(this.x + this.w / 2, this.y, obj.x - obj.w / 2 , obj.y);
  } else if(obj.flag == "condition") {
    arrow = new Arrow(this.x + this.w / 2, this.y, obj.x-obj.l*2 , obj.y);
  }else if(obj.flag == "start" || obj.flag == "end"){
    arrow = new Arrow(this.x + this.w / 2, this.y, obj.x-obj.w/2 , obj.y);
  }
  arrow.drawLeftToRightOrRightToLeft(context);
}

//箭头从Condition菱形Bottom——>top
Condition.prototype.drawBottomToTop = function(obj,context) {
  if(obj.flag == "step") {
    var arrow = new Arrow(this.x, this.y + this.h, obj.x, obj.y - obj.h / 2);
    arrow.drawBottomToTop(context);
  } else if(obj.flag == "condition") {
    var arrow = new Arrow(this.x, this.y + this.l, obj.x, obj.y - obj.l);
    arrow.drawBottomToTop(context);
  }
}
//箭头从Condition菱形right——>top
Condition.prototype.drawRightToTop = function(obj, context) {
  if(obj.flag == "step") {
    var arrow = new Arrow(this.x + this.l * 2, this.y, obj.x, obj.y - obj.h / 2);
    arrow.drawLeftOrRightToTop(context);
  } else if(obj.flag == "condition") {
    var arrow = new Arrow(this.x + this.l * 2, this.y, obj.x, obj.y - obj.l);
    arrow.drawLeftOrRightToTop(context);
  }
}
//箭头从Condition菱形left——>top
Condition.prototype.drawLeftToTop = function(obj,context) {
  if(obj.flag == "step") {
    var arrow = new Arrow(this.x - this.l * 2, this.y, obj.x, obj.y - obj.h / 2);
    arrow.drawLeftOrRightToTop(context);
  } else if(obj.flag == "condition") {
    var arrow = new Arrow(this.x - this.l * 2, this.y, obj.x, obj.y - obj.l);
    arrow.drawLeftOrRightToTop(context);
  }
}
//箭头从Condition菱形right——>left
Condition.prototype.drawRightToLeft = function(obj,context) {
  if(obj.flag == "step") {
    var arrow = new Arrow(this.x + this.l * 2, this.y, obj.x - this.w / 2, obj.y);
    arrow.drawLeftToRightOrRightToLeft(context);
  } else if(obj.flag == "condition") {
    var arrow = new Arrow(this.x + this.l * 2, this.y, obj.x - this.l * 2, obj.y);
    arrow.drawLeftToRightOrRightToLeft(context);
  }
}
//箭头从Condition菱形left——>right
Condition.prototype.drawLeftToRight = function(obj, context) {
  if(obj.flag == "step") {
    var arrow = new Arrow(this.x - this.l * 2, this.y, obj.x + this.w / 2, obj.y);
    arrow.drawLeftToRightOrRightToLeft(context);
  } else if(obj.flag == "condition") {
    var arrow = new Arrow(this.x - this.l * 2, this.y, obj.x + this.l * 2, obj.y);
    arrow.drawLeftToRightOrRightToLeft(context);
  }
}

/////////////////////////////////////////画箭头start/////////////////////////////////////
function Arrow(x1, y1, x2, y2) {
  this.x1 = x1;
  this.y1 = y1;
  this.x2 = x2;
  this.y2 = y2;
  this.tmpX1 = null;
  this.tmpY1 = null;
  this.tmpX2 = null;
  this.tmpY2 = null;
  this.color = "#5B9BD5";

}
Arrow.prototype.setColor = function(color) {
  this.color=color;
}
/**
 *
 * @param {Object} x1起始点横坐标
 * @param {Object} y1起始点纵坐标
 * @param {Object} x2结束点横坐标
 * @param {Object} y2结束点纵坐标
 */
Arrow.prototype.setP = function(x1, y1, x2, y2) {
  this.x1 = x1;
  this.y1 = y1;
  this.x2 = x2;
  this.y2 = y2;
}
//第一个拐点
Arrow.prototype.setP1 = function(tmpX1,tmpY1) {
  this.tmpX1=tmpX1;
  this.tmpY1=tmpY1;
}
//第二个拐点
Arrow.prototype.setP2 = function(tmpX2,tmpY2) {
  this.tmpX2=tmpX2;
  this.tmpY2=tmpY2;
}
Arrow.prototype.drawBottomToTop = function(ctx) {
  if (this.x1 != this.x2) {
    this.setP1(this.x1,(this.y1+this.y2)/2);
    this.setP2(this.x2,(this.y1+this.y2)/2);
    this.draw(ctx);
  }else{
    this.draw(ctx);
  }
}
Arrow.prototype.drawLeftOrRightToTop = function(ctx) {
  this.setP1(this.x2,this.y1);
  this.draw(ctx);
}
Arrow.prototype.drawLeftToRightOrRightToLeft = function(ctx) {
  if (this.y1 != this.y2) {
    this.setP1((this.x1+this.x2)/2,this.y1);
    this.setP2((this.x1+this.x2)/2,this.y2);
    this.draw(ctx);
  }else{
    this.draw(ctx);
  }
}
Arrow.prototype.drawBottomToRight = function(ctx) {
  if (this.y1 != this.y2) {
    this.setP1(this.x1,this.y2);
    this.draw(ctx);
  }else{
    this.draw(ctx);
  }
}
Arrow.prototype.draw = function(ctx) {
  // arbitrary styling
  ctx.strokeStyle = this.color;
  ctx.fillStyle = this.color;
  // draw the line
  ctx.beginPath();
  ctx.moveTo(this.x1, this.y1);
  if(this.tmpX1 != null && this.tmpY1 != null && this.tmpX2 != null && this.tmpY2 != null) {
    ctx.lineTo(this.tmpX1, this.tmpY1);
    ctx.closePath();
    ctx.stroke();
    ctx.beginPath();
    ctx.moveTo(this.tmpX1, this.tmpY1)
    ctx.lineTo(this.tmpX2, this.tmpY2);
    ctx.closePath();
    ctx.stroke();
    ctx.beginPath();
    ctx.moveTo(this.tmpX2, this.tmpY2);
    ctx.lineTo(this.x2, this.y2);
    ctx.closePath();
    ctx.stroke();
    var endRadians = Math.atan((this.y2 - this.tmpY2) / (this.x2 - this.tmpX2));
    endRadians += ((this.x2 >= this.tmpX2) ? 90 : -90) * Math.PI / 180;
    this.drawArrowhead(ctx, this.x2, this.y2, endRadians);
  } else if(this.tmpX1 != null && this.tmpY1 != null && this.tmpX2 == null && this.tmpY2 == null) {
    ctx.lineTo(this.tmpX1, this.tmpY1);
    ctx.closePath();
    ctx.stroke();
    ctx.beginPath();
    ctx.moveTo(this.tmpX1, this.tmpY1)
    ctx.lineTo(this.x2, this.y2);
    ctx.closePath();
    ctx.stroke();
    var endRadians = Math.atan((this.y2 - this.tmpY1) / (this.x2 - this.tmpX1));
    endRadians += ((this.x2 >= this.tmpX1) ? 90 : -90) * Math.PI / 180;
    this.drawArrowhead(ctx, this.x2, this.y2, endRadians);
  }else if(this.tmpX1 == null && this.tmpY1 == null && this.tmpX2 == null && this.tmpY2 == null){
    ctx.lineTo(this.x2, this.y2);
    ctx.closePath();
    ctx.stroke();
    var endRadians = Math.atan((this.y2 - this.y1) / (this.x2 - this.x1));
    endRadians += ((this.x2 >= this.x1) ? 90 : -90) * Math.PI / 180;
    this.drawArrowhead(ctx, this.x2, this.y2, endRadians);
  }
}
Arrow.prototype.drawArrowhead = function(ctx, x, y, radians) {
  ctx.save();
  ctx.beginPath();
  ctx.translate(x, y);
  ctx.rotate(radians);
  ctx.moveTo(0, 0);
  ctx.lineTo(5, 10);
  ctx.lineTo(-5, 10);
  ctx.closePath();
  ctx.restore();
  ctx.fill();
}
/////////////////////////////////////////画箭头end/////////////////////////////////////

html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <link rel="stylesheet" href="public.css">
</head>
<body>
<div class="box">
    <canvas id="myCanvas" width="1000" height="800"></canvas>
</div>
<script type="text/javascript" src="drawFlowChart.js" ></script>
<script>
    var canvas = document.getElementById("myCanvas");
    var cxt = canvas.getContext('2d');
    var canWidth = cxt.canvas.clientWidth;
    var init = {top: 32, spaceH: 70};
    var row2 = {
        y:init.top+init.spaceH,
        data:[
            {
                type:'Step',
                text:'业务名称1',
                name:'step_2_1',
                arrowArr:[
                    {
                        arrow:'drawBottomToTop',
                        to:'step_3_1'
                    }
                ],
                x:'',
                y:'',
                requestData:{}
            },
            {
                type:'Step',
                text:'业务名称2',
                name:'step_2_2',
                arrowArr:[
                    {
                        arrow:'drawBottomToLeft',
                        to:'step_3_2'
                    }
                ]
            },
            {
                type:'Step',
                text:'业务名称3',
                name:'step_2_3',
                arrowArr:[
                    {
                        arrow:'drawBottomToRight',
                        to:'step_3_2'
                    }
                ]
            },
            {
                type:'Step',
                name:'step_2_4',
                text:'业务名称4',
                arrowArr:[
                    {
                        arrow:'drawBottomToRight',
                        to:'step_7_1'
                    }
                ]
            }
        ]
    };
    row2.data = calChartX(canWidth,row2.data, row2.y);
    var flowData = [
        {
            row:1,
            y:init.top,
            data:[
                {
                    type:'Start',
                    text:'开始',
                    name:'step_1_1',
                    arrowArr:[
                        {
                            arrow:'drawBottomToTop',
                            to:'step_2_1'
                        },
                        {
                            arrow:'drawBottomToTop',
                            to:'step_2_2'
                        },
                        {
                            arrow:'drawBottomToTop',
                            to:'step_2_3'
                        }, {
                            arrow:'drawBottomToTop',
                            to:'step_2_4'
                        }
                    ],
                    x:canWidth/2,
                    y:''
                }
            ]
        },
        {
            row:2,
            y:init.top+init.spaceH,
            data:row2.data,
            method:{
                onmousemove:null,
                onmouseleave:null,
                onclick:hoverSingleChart
            }
        },
        {
            row:3,
            y:'',
            data:[{
                type:'Step',
                text:'业务名称4',
                x:row2.data[0].x,
                name:'step_3_1',
                arrowArr:[
                    {
                        arrow:'drawBottomToTop',
                        to:'step_4_1'
                    }
                ]
            },{
                type:'Step',
                text:'业务名称5',
                name:'step_3_2',
                x:canWidth/2,
                arrowArr:[
                    {
                        arrow:'drawBottomToTop',
                        to:'step_4_2'
                    }
                ]
            }]
        },
        {
            row:4,
            y:'',
            data:[{
                type:'Step',
                text:'业务名称6',
                x:row2.data[0].x,
                name:'step_4_1',
                arrowArr:[
                    {
                        arrow:'drawBottomToTop',
                        to:'step_5_1'
                    }
                ]
            },{
                type:'Step',
                text:'业务名称7',
                name:'step_4_2',
                x:canWidth/2,
                arrowArr:[
                    {
                        arrow:'drawBottomToTop',
                        to:'step_5_2'
                    }
                ]
            }]
        },
        {
            row:5,
            y:'',
            data:[{
                type:'Step',
                text:'业务名称8',
                x:row2.data[0].x,
                name:'step_5_1',
                arrowArr:[
                    {
                        arrow:'drawBottomToTop',
                        to:'step_6_1'
                    }
                ]
            },{
                type:'Step',
                text:'业务名称9',
                name:'step_5_2',
                x:canWidth/2,
                arrowArr:[
                    {
                        arrow:'drawBottomToTop',
                        to:'step_6_2'
                    },
                    {
                        arrow:'drawBottomToTop',
                        to:'step_6_3'
                    }
                ]
            }]
        },
        {
            row:6,
            y:'',
            data:[{
                type:'Step',
                text:'业务名称10',
                x:row2.data[0].x,
                name:'step_6_1',
                arrowArr:[
                    {
                        arrow:'drawBottomToLeft',
                        to:'step_7_1'
                    }
                ]
            },{
                type:'Step',
                text:'业务名称11',
                name:'step_6_2',
                x:row2.data[1].x,
                arrowArr:[
                    {
                        arrow:'drawBottomToTop',
                        to:'step_7_1'
                    }
                ]
            },{
                type:'Step',
                text:'业务名称12',
                name:'step_6_3',
                x:row2.data[2].x,
                arrowArr:[
                    {
                        arrow:'drawBottomToTop',
                        to:'step_7_1'
                    }
                ]
            }]
        },
        {
            row:7,
            y:init.top+init.spaceH*6+10,
            data:[{
                type:'Condition',
                text:'判断条件',
                x:canWidth/2,
                name:'step_7_1',
                arrowArr:[
                    {
                        arrow:'drawBottomToTop',
                        to:'step_8_1'
                    }
                ]
            }]
        },
        {
            row:8,
            y:init.top+init.spaceH*7+30,
            isAverage:true, //平均计算x
            data:[
                {
                    type:'Step',
                    text:'业务名称12',
                    name:'step_8_1',
                    arrowArr:[
                        {
                            arrow:'drawRightToLeft',
                            to:'step_8_2'
                        }
                    ],
                    requestData:{},
                    method:{
                        onmousemove:null,
                        onmouseleave:null,
                        onclick:null
                    }
                },
                {
                    type:'Step',
                    text:'业务名称4',
                    name:'step_8_2',
                    arrowArr:[
                        {
                            arrow:'drawRightToLeft',
                            to:'step_8_3'
                        }
                    ]
                },
                {
                    type:'Step',
                    text:'业务名称4',
                    name:'step_8_3',
                    arrowArr:[
                        {
                            arrow:'drawRightToLeft',
                            to:'step_8_4'
                        }
                    ]
                },
                {
                    type:'Step',
                    name:'step_8_4',
                    text:'业务名称4',
                    arrowArr:[
                        {
                            arrow:'drawRightToLeft',
                            to:'step_8_5'
                        }
                    ]
                },
                {
                    type:'Step',
                    name:'step_8_5',
                    text:'业务名称4',
                    arrowArr:[
                        {
                            arrow:'drawRightToLeft',
                            to:'step_8_6'
                        }
                    ]
                },
                {
                    type:'Step',
                    name:'step_8_6',
                    text:'业务名称4',
                    arrowArr:[
                        {
                            arrow:'drawBottomToTop',
                            to:'step_9_1'
                        }
                    ]
                }
            ]
        },
        {
            row:9,
            y:init.top+init.spaceH*8+30,
            isAverage:true,
            data:[
                {
                    type:'Step',
                    text:'业务名称4',
                    name:'step_9_1',
                    arrowArr:[
                        {
                            arrow:'drawRightToLeft',
                            to:'step_9_2'
                        }
                    ],
                    requestData:{},
                    method:{
                        onmousemove:null,
                        onmouseleave:null,
                        onclick:hoverSingleChart
                    }
                },
                {
                    type:'Step',
                    text:'业务名称4',
                    name:'step_9_2',
                    arrowArr:[
                        {
                            arrow:'drawRightToLeft',
                            to:'step_9_3'
                        }
                    ]
                },
                {
                    type:'Step',
                    text:'业务名称4',
                    name:'step_9_3',
                    arrowArr:[
                        {
                            arrow:'drawRightToLeft',
                            to:'step_9_4'
                        }
                    ]
                },
                {
                    type:'Step',
                    name:'step_9_4',
                    text:'业务名称4',
                    arrowArr:[
                        {
                            arrow:'drawRightToLeft',
                            to:'step_9_5'
                        }
                    ]
                },
                {
                    type:'End',
                    name:'step_9_5',
                    text:'结束',
                    arrowArr:[]
                }
            ]
        }
    ];
    drawFlowChart(cxt,canvas,flowData, init.top, init.spaceH);

    function hoverSingleChart(singleData){
        console.log("---------鼠标事件-----------");
        console.log(singleData);
    }

</script>
</body>
</html>

参考博文：https://www.cnblogs.com/DurantSimpson/p/6146038.html/