html5利用canvas绘画二级树形结构图

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 = '<p class="main-target">' + data + '</p>';

    $('.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 = '<p class="item-text">' + data + '</p>';

    $('.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}

}