popover组件里有个_getSupportOffset的作用是什么呀?

[sonicsunsky]

能不能说明一下_getSupportOffset()这个函数的实现步骤和思路，一共12个方向看得我有点懵逼，求助大神讲解一下

[ChanceYu]

这个方法是获取某个元素所支持的弹出菜单箭头方位，由上右下左中组合而成，每个方向有三种方位，一共上下左右四个方向，3x4=12，例如：弹出菜单箭头朝上，那么就有：上左、上中、上右三种方位

[sonicsunsky]

嗯，大概思路知道了，主要还是对于代码里的一些变量的含义还是不太明确，比如: boxTotalWidth=boxWidth + 8; pointTop; elemCenterLeft/Right/Top/Bottom; elemEdgeLeft/Right/Top/Bottom;

还有 elemEdgeBottom > boxTotalHeight && elemCenterRight > boxWidth + 16 这些个判断条件怎么来的? 最好有个坐标系的说明

` // page let pageWidth = pageRect.width; let pageHeight = pageRect.height;

// view 
let viewTop = viewRect.scrollTop;

// box
let boxWidth = boxRect.width;
let boxHeight = boxRect.height;
let boxTotalWidth = boxWidth + 8;
let boxTotalHeight = boxHeight + 8;

// elem
let elemWidth = elemRect.width;
let elemHeight = elemRect.height;
let elemTop = elemRect.top;
let elemLeft = elemRect.left;

// point
let pointTop = viewTop + elemTop;

let elemCenterLeft = elemLeft + elemWidth / 2;
let elemCenterRight = pageWidth - elemCenterLeft;
let elemCenterTop = pointTop + elemHeight / 2;
let elemCenterBottom = pageHeight - elemCenterTop;

let elemEdgeLeft = elemLeft;
let elemEdgeRight = elemCenterRight - elemWidth / 2;
let elemEdgeTop = pointTop;
let elemEdgeBottom = elemCenterBottom - elemHeight / 2;

// tl let TTop = elemEdgeTop + elemHeight + 8;

if (elemEdgeBottom > boxTotalHeight
  && elemCenterRight > boxWidth + 16){
  result.supports.push('tl');
  result.tl = {};
  result.tl.left = elemCenterLeft - 16;
  result.tl.top = TTop;
}

// tr
if (elemEdgeBottom > boxTotalHeight
  && elemCenterLeft > boxWidth + 16) {
  result.supports.push('tr');
  result.tr = {};
  result.tr.left = elemCenterLeft - boxWidth + 16;
  result.tr.top = TTop;
}

// tc
if (elemEdgeBottom > boxTotalHeight
  && elemCenterRight > boxWidth + 16
  && elemCenterLeft > boxWidth + 16) {
  result.supports.push('tc');
  result.tc = {};
  result.tc.left = elemCenterLeft - boxWidth / 2;
  result.tc.top = TTop;
}

`