html5利用canvas绘画二级树形结构图的示例有哪些。

function startDrag(ev) {
  ev.dataTransfer.setData("Text",ev.target.innerText);
}

function allowDrop(ev) {
  ev.preventDefault();
}

function decideDrop(ev) {
  ev.preventDefault();
  var length = $('.main-target').length;
  if(length == 0){
    dropToMain(ev);
  }else {
    dropToRelate(ev);
  }
}

function dropToMain(ev) {
  var data=ev.dataTransfer.getData("Text");
  var _html = '<div class="main-target">' + data + '</div>';
  $('.main-target-wrap').width('auto').append(_html);
}

function dropToRelate(ev) {
  //画关系线
  drawLineOne(document.getElementById('canvasOne'), 'begin');
  drawLineOne(document.getElementById('canvasTwo'), 'end');

  //插入图片 以及图片初始化点击事件
  var _img = $('<img src="inner.png">');
  $('.imgBox').append(_img);
  _img.click(showRelationBox);
  //写入数据
  var data = ev.dataTransfer.getData('Text');
  var _html = '<div class="item-text">' + data + '</div>';
  $('.relation-text-box').append(_html);
}

function drawLineOne(canvas, flag) {
  var context = canvas.getContext('2d');
  var position = {};
  if(flag == "begin"){
    position = getCanvasOnePosition();
  }else {
    position = getCanvasTwoPosition();
  }
  context.beginPath();
  context.moveTo(position.beginX, position.beginY);
  context.lineTo(position.endX, position.endY);
  if(position.endX2 && position.endY2){
    context.lineTo(position.endX2, position.endY2);
  }
  context.strokeStyle = "#333";
  context.stroke();
}

/**
 * 左侧关系线
 * @returns {{beginX: *, beginY: *, endX: *, endY: *}}
 */
function getCanvasOnePosition() {
  var imgLength = $('.imgBox img').length;
  var beginX = (imgLength == 0) ? 0 : 77,
    beginY = (imgLength == 0) ? 15 : (15 + 60 * (imgLength-1)),
    endX = (imgLength == 0) ? 155 : 77,
    endY = 60*imgLength + 15;
  var position = {beginX: beginX, beginY: beginY, endX: endX, endY: endY};
  if(imgLength > 0){
    position.endX2 = 155;
    position.endY2 = endY;
  }
  return position;
}

function getCanvasTwoPosition() {
  var imgLength = $('.imgBox img').length;
  var endY = 15 + 60*imgLength
  return {beginX: 0, beginY: endY, endX: 155, endY: endY}
}