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phab/webroot/rsrc/js/application/core/behavior-buoyant.js
a22827865f8afeature/testing

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behavior-buoyant.js
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/**
* @provides javelin-behavior-buoyant
* @requires javelin-behavior
* javelin-stratcom
* javelin-vector
* javelin-dom
*/
JX.behavior('buoyant', function() {
// The display element which shows the "buoyant" header to the user.
var element = JX.$N('div', {className : 'buoyant'});
// Keeps track of whether we're currently showing anything or not.
var visible = false;
// If we're showing something, the positional DOM element that triggered the
// currently shown header.
var active_marker = null;
// When the header is clicked, jump to the element that triggered it.
JX.DOM.listen(element, 'click', null, function(e) {
window.scrollTo(0, JX.$V(active_marker).y - 40);
});
function hide() {
if (visible) {
JX.DOM.remove(element);
visible = false;
}
}
function show(text) {
if (!visible) {
document.body.appendChild(element);
visible = true;
}
JX.DOM.setContent(element, text);
}
var onviewportchange = function(e) {
// If we're currently showing a header but we've scrolled back up past its
// marker, hide it.
var scroll_position = JX.Vector.getScroll().y;
if (visible && (scroll_position < JX.$V(active_marker).y)) {
hide();
}
// Find all the markers in the document.
var markers = JX.DOM.scry(document.body, 'div', 'buoyant');
// Sort the markers by Y position, descending.
var markinfo = [];
for (var ii = 0; ii < markers.length; ii++) {
markinfo.push({
marker: markers[ii],
position: JX.$V(markers[ii]).y
});
}
markinfo.sort(function(u, v) { return (v.position - u.position); });
// Find the first marker above the current scroll position.
for (var ii = 0; ii < markinfo.length; ii++) {
if (markinfo[ii].position > scroll_position) {
// This marker is below the current scroll position, so ignore it.
continue;
}
// We've found a marker. Display it as appropriate;
active_marker = markinfo[ii].marker;
var text = JX.Stratcom.getData(active_marker).text;
if (text) {
show(text);
} else {
hide();
}
break;
}
}
JX.Stratcom.listen('scroll', null, onviewportchange);
JX.Stratcom.listen('resize', null, onviewportchange);
});
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