Function measureLineInner

static/js/codemirror/codemirror.js:974–1042

(cm, line)

  }

  function measureLineInner(cm, line) {
    var display = cm.display, measure = emptyArray(line.text.length);
    var pre = lineContent(cm, line, measure);

    // IE does not cache element positions of inline elements between
    // calls to getBoundingClientRect. This makes the loop below,
    // which gathers the positions of all the characters on the line,
    // do an amount of layout work quadratic to the number of
    // characters. When line wrapping is off, we try to improve things
    // by first subdividing the line into a bunch of inline blocks, so
    // that IE can reuse most of the layout information from caches
    // for those blocks. This does interfere with line wrapping, so it
    // doesn't work when wrapping is on, but in that case the
    // situation is slightly better, since IE does cache line-wrapping
    // information and only recomputes per-line.
    if (ie && !ie_lt8 && !cm.options.lineWrapping && pre.childNodes.length > 100) {
      var fragment = document.createDocumentFragment();
      var chunk = 10, n = pre.childNodes.length;
      for (var i = 0, chunks = Math.ceil(n / chunk); i < chunks; ++i) {
        var wrap = elt("div", null, null, "display: inline-block");
        for (var j = 0; j < chunk && n; ++j) {
          wrap.appendChild(pre.firstChild);
          --n;
        }
        fragment.appendChild(wrap);
      }
      pre.appendChild(fragment);
    }

    removeChildrenAndAdd(display.measure, pre);

    var outer = getRect(display.lineDiv);
    var vranges = [], data = emptyArray(line.text.length), maxBot = pre.offsetHeight;
    // Work around an IE7/8 bug where it will sometimes have randomly
    // replaced our pre with a clone at this point.
    if (ie_lt9 && display.measure.first != pre)
      removeChildrenAndAdd(display.measure, pre);

    for (var i = 0, cur; i < measure.length; ++i) if (cur = measure[i]) {
      var size = getRect(cur);
      var top = Math.max(0, size.top - outer.top), bot = Math.min(size.bottom - outer.top, maxBot);
      for (var j = 0; j < vranges.length; j += 2) {
        var rtop = vranges[j], rbot = vranges[j+1];
        if (rtop > bot || rbot < top) continue;
        if (rtop <= top && rbot >= bot ||
            top <= rtop && bot >= rbot ||
            Math.min(bot, rbot) - Math.max(top, rtop) >= (bot - top) >> 1) {
          vranges[j] = Math.min(top, rtop);
          vranges[j+1] = Math.max(bot, rbot);
          break;
        }
      }
      if (j == vranges.length) vranges.push(top, bot);
      var right = size.right;
      if (cur.measureRight) right = getRect(cur.measureRight).left;
      data[i] = {left: size.left - outer.left, right: right - outer.left, top: j};
    }
    for (var i = 0, cur; i < data.length; ++i) if (cur = data[i]) {