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Sticky Bootstrap column should end with parent/content

I have seen various forms of this problem but nothing really helped me to solve the partial sticky sidebar/Bootstrap column behaviour. Let me start with the problem itself.
There is a big image close to the top of my page. Because of the page complexity, I am using Bootstrap column grid. The image spans over, let's say, 10 columns and I have left 2, belonging to the same row, on the left side to store a sidebar. This also allows me to vertically align the sidebar next to the image.
Now, the sidebar, what is now a Bootstrap column, should go sticky and should stay vertically aligned to the viewport once the scrollbar passes by. You can see in the fiddle that it kind of "jumps" instead of transitioning smoothly.
The other problem is that the sticky element/column should only remain sticky as long as its parent/container is visible. Which means that it should transition/be relative to the end of that container. Right now I have only managed to keep it sticky till the end of the page. It should stop above the red line (depicted in the fiddle).
Here is my jQuery logic so far.
$(document).ready(function(){
$(window).scroll(function(){
var elem = $("#refScroller").offset().top - ($("#refScroller").height() / 2);
var windowvalue = $(window).scrollTop();
if (elem <= windowvalue) {
$("#wannabeSticky").addClass("sticky");
}
else {
$("#wannabeSticky").removeClass("sticky");
}
});
});
I would really appreciate some ideas and hints as this has been bothering me for two days. I would love to keep the Bootstrap grid structure if possible, but feel free to give any suggestions, even those who depict the sidebar as a pure absolute div, as long as the sticky-ness works.
Thanks in advance!
EDIT: I know there is a similar problem already here, but it seems I can't make the JS logic work for my case.

So, having spent another day on it, it seems I reached a decent jQuery version that gets the job done. There is my updated fiddle.
$(document).ready(function(){
var passedMobileNavi = false;
function stickySocialNavi(reference, valueExtracted) {
var refTop = $(reference).offset().top - valueExtracted;
var scrollTop = $(window).scrollTop();
return (refTop <= scrollTop);
}
$(window).scroll(function() {
if (stickySocialNavi($("#refScroller"), $("#refScroller").height())) {
if (!passedMobileNavi) {
passedMobileNavi = true;
$("#wannabeSticky").addClass("sticky");
}
}
else {
passedMobileNavi = false;
$("#wannabeSticky").removeClass("sticky");
}
if (stickySocialNavi($("#end"), $(window).height())) {
var var1 = $(window).scrollTop(),
var2 = $("#end").offset().top,
var3 = $(window).height();
var calculateOffset = (var2 - var3) - var1;
$("#wannabeSticky").css("top", "calc(50% + " + calculateOffset + "px)");
}
else {
$("#wannabeSticky").css("top", "50%");
}
});
});
For the sticky-ness to start, I took the reference point (which is the non-moving element right next to it) and its height. The sticky element gets a fixed position as long as the scrollbar goes past the reference point's center.
As the stick element is centered, it gets additional top offset values when the end of its container is reached. It is still fixed, but its top property's value takes the scroll difference, thus slowly depicting it towards the end of the container.
I don't know if this is the most elegant, straightforward, or easy to implement/understand solution, but it worked for me.

Freeze element (position:fixed) for specific scroll range

I'm working on this site (http://styleguide.co/medhelp/) that has 5 sections. For one of the sections (Styles), I've got a sidenav I'm trying to get to stick in the visible frame only as long as users are scrolling in that section.
Here's what I've done thus far - I'm telling the section title & sidenav to stick after the top of the section has begun:
$(window).scroll(function(event) {
var sw = $('.fixed'),
pg = $('.styles'),
diff = pg[0].offsetTop - window.pageYOffset;
if (diff < 80 ) {
$('.fixed').css('position', 'fixed');
$('.fixed').css('top', '160px');
$('.styles').css('position', 'fixed');
$('.styles').css('top', '70px');
}
else {
$('.fixed').css('position', 'relative');
$('.fixed').css('top', '0px');
$('.styles').css('position', 'relative');
$('.styles').css('top', '0px');
}
});
I can't seem to figure out a good way to make the section title "Style" and the sidenav appear/disappear while I scroll to/from that section. Any advice? What could I do better? A simple solution demo in jsfiddle would really help!
Please click on this link & scroll down/up to know what I'm referring to: http://styleguide.co/medhelp/

I'm not going to give you a fiddle, but you need to determine when the next section would stick based on its offset from the top. At the moment what you are doing is:
// if difference top and element < 80 -> fix to top, else position is relative
First of all this means the condition will never be undone. What you need to do in order to continue is:
// once next contact section comes into screen
//(offset from the top of the screen <= screen height), give
var winHeight = $(window).height();
var calcTop = 80 - (winHeight - (winHeight - $('#nextSelector').offset().top);
$('.fixed').css('top', calcTop);
This will give the illusion of your text scrolling up as the new section comes up. I hope this helps. Also, when scrolling back up it doesn't re-stick, but you probably are aware of that.

Jquery change div based on another div's position

Let me start of by saying, I'm just now learning JS and Jquery, so my knowledge is very limited.
I've been looking around for 2 days now, and tried all sorts of combinations. But I just can't get this to work.
Below is an example of the layout
I'm looking for a way to trigger an event when div 1 is X px from the top of the screen. Or when div 1 collides with div 2.
What I'm trying to accomplish is to change the css of div 2 (the fixed menu) when div 1 is (in this case) 100px from the top of screen (browser window). Alternatively, when div1 passes div2 (I'm using responsive design, so the fixed height from top might become a problem on smaller screens right? Seeing as the header for example won't be there on a hand held.). So maybe collision detection is better here? Would really appreciate some thoughts and input on this matter.
Another issue is, div2 has to revert back to is previous css once div1 passes it (going back (beyond the 100px)).
This is what I have but it has no effect
$(document).ready(function() {
var content = $('#div1');
var top = $('#div2');
$(window).on('scroll', function() {
if(content.offset().top <= 100) {
top.css({'opacity': 0.8});
}else{
top.css({'opacity': 1});
}
});
});

I am not sure of the reason but $("#content").offset().top was giving a constant value on console. So I added window.scrollTOp() to check its distance from top, here is how it works,
$(document).ready(function() {
var top = $("#menu");
$(window).on('scroll', function(){
if(($('#content').offset().top - $(window).scrollTop()) <= 100){
top.css({'opacity': 0.4});
}else{
top.css({'opacity': 1});
}
});
});
And DEMO JSFIDDLE....

Make a div appear when scrolling past a certain point of a page

My goal is to make a fixed div appear at the top of a page once someone scrolls a certain amount of pixels down the page. Basically once the header section is out of view, this div will appear.
I've looked at code similar to what I want; however, haven't seen anything that would allow me to easily modify the pixel count from the top of the page (if possible).
Here is a piece of code I saw dealing with making divs appear by scrolling.
// Get the headers position from the top of the page, plus its own height
var startY = $('header').position().top + $('header').outerHeight();
$(window).scroll(function(){
checkY();
});
function checkY(){
if( $(window).scrollTop() > startY ){
$('.fixedDiv').slideDown();
}else{
$('.fixedDiv').slideUp();
}
}
// Do this on load just in case the user starts half way down the page
checkY();
I just want to know how to make it appear. If someone knows of a piece of code already in tact with a slide up and slide down animation, that would be greatly appreciated as well but not required.

window.addEventListener("scroll",function() {
if(window.scrollY > 500) {
$('.fixedDiv').slideDown();
}
else {
$('.fixedDiv').slideUp();
}
},false);

Brandon Tilley answered my question in a comment...
You would change the first line, with the startY, to be the specific Y
position you need, rather than calculating based on the header's
position and height. Here's an updated fiddle:
jsfiddle.net/BinaryMuse/Ehney/1

window.addEventListener("scroll",function() {
$('.fixedDiv')[(window.scrollY > 500)?"slideDown":"slideUp"]();
},false);
DEMO: http://jsfiddle.net/DerekL/8eG2A/

Efficient way to select elements touching top edge of viewport

What would be computationally-efficient ways to select elements touching the top edge of browser window viewport as the page is scrolled?
See attached image. Green elements are selected because they are touching the top edge.
UPDATE
An example of how I'll use this is to fade elements that are going off-screen. There may be hundreds of them on the page. Imagine a page like Pinterest. Computing offset and scrollTop for hundreds of them at the rate of scroll event, even if throttled still feels really inefficient.

This is what I came up with. I think that it could be improved upon by caching the scrollTop values, but this is pretty good. I have included the framework for caching the boxtops, but not the implementation code. I have also only implemented scrolling down to hide divs. I have left reshowing them on upscroll as an exercise for you.
When the window is scrolled we get the last hidden div. We know that everything before this div is already hidden. Then use a 'while next element is off the screen' hide it. As soon as a div isn't off the screen we abort. Thus saving time from iterating through the entire list.
http://jsfiddle.net/kkv3h/2/
//track whether user has scrolled up or down
var prevScrollTop = $(document).scrollTop();
$(document).scroll(function() {
var currentScrollTop = $(this).scrollTop();
if (currentScrollTop > prevScrollTop) {
//down
var lasthiddenbox = $('.fadeboxhidden:last');
var nextbox = (lasthiddenbox.length > 0) ? lasthiddenbox.next('.fadebox') : $('.fadebox:first');
while (nextbox.length) {
console.log('box: ' + nextbox.offset().top + ' scroll: ' + currentScrollTop);
if (nextbox.offset().top < currentScrollTop) {
nextbox.animate({ opacity: 0 }, 3000).addClass('fadeboxhidden');
}
else { return; }
nextbox = nextbox.next('.fadebox:first');
}
} else {
//up
}
prevScrollTop = currentScrollTop ;
});
//create an object to hold a list of box top locations
var boxtops = new Object;
//gather all boxes and store their top location
$('.fadebox').each( function(index) {
//you may want to dynamically generate div ids here based on index. I didn't do this
//because i was already using the id for positioning.
var divid = $(this).prop('id');
boxtops[divid] = $(this).offset().top;
//console.log(boxtops[divid]);
});

I'm thinking the best way would be that you could mark elements you want to determine hit testing with by some class, say "hit-test-visible" or something. Then, for those elements, on the scroll event, you should be able to find their offset compared to the document - see jQuery offset, and then based on the scroll value, if the offset is less than the scroll, and the offset + element height is greater than the scroll offset, then the element should be "touching" the top edge.