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Execute code after scrolling a certain amount of pixels from a certain point (up or down)

I'm currently making an overlay that covers a sticky top bar when the user has scrolled beyond a certain point (down) and disappears when scrolling back up. However, I'd like to be able to scroll for at least 50px before the code is executed (something like a gap before the overlay is triggered).
$(function() {
var prevScroll = $(document).scrollTop(); //initial position
$(window).scroll(function() {
var newScroll = $(document).scrollTop(); //position from top after scrolling
if(newScroll > prevScroll) { // checks if the user has scrolled up or down
var fromNew = $(document).scrollTop(); // holds value to compare with the position + gap amount
if (fromNew > newScroll + 50) { //checks to see if scrolled for 50px
$("#stick-start").fadeIn("fast");
prevScroll = newScroll + 50; //initial position + scrolled amount
};
} else {
var fromNew = $(document).scrollTop();
if (fromNew > newScroll - 50) {
if ($("#stick-start").hasClass("is-stuck")) {
$("#stick-start").fadeOut("fast");
prevScroll = newScroll - 50;
};
};
};
});
});
The condition that checks whether you're scrolling up or down works. But as it is now, the overlay just keeps fading in and out repeatedly. How do I make it so that you have to scroll at least 50px before anything happens ?

I think this should get you where you're going.
var $document = $(document);
$(window).scroll(function() {
if ($document.scrollTop() >= 50) {
$("#stick-start").fadeIn("fast");
} else {
$("#stick-start").fadeOut("fast");
}
});
EDIT: had an error, should be good now.

$(window).scroll(function() {
if ($(this).scrollTop() >= 50) {
$("#stick-start").fadeIn();
} else {
$("#stick-start").fadeOut();
}
});

Jquery scroll with scrollTop Position is really slow to scroll

I have infinity scroll and each time the top scroll reach to certain part of the div, it loads a new content until its over. But each time it loads, it get very slow. It happens when I put some code inside of .each function, and that my scroll becomes really slow, which is annoying. I don't know how to fix it
function scrollAnimationFrame(ticking, windowHeight, tabSelected){
if (!ticking) {
window.requestAnimationFrame(function() {
scrollEvent(tabSelected, windowHeight);
ticking = false;
});
}
ticking = true;
}
function scrollEvent(tabSelected, windowHeight) {
var activeTab = document.getElementsByName(tabSelected)[0]
var divResults = activeTab.getElementsByClassName('div-content');
var scrollY = window.scrollY || document.documentElement.scrollTop;
var pos = $(window).scrollTop();
var scrollY = window.scrollY || document.documentElement.scrollTop;
$(divResults).each(function(i, el){
var posOutsideDiv = $(el).offset().top + $(el).outerHeight();
var inside = (scrollY >= $(el).offset().top && scrollY <= posOutsideDiv - 150)
if(inside){
toggleThead(el, "visible");
} else if(scrollY >= $(el).offset().top && scrollY <= posOutsideDiv + $(document).height()){
toggleThead(el, "hidden");
} else {
toggleThead(el, "visible");
}
});
}

Okay, I thought it was javascript that the scroll is getting slower each time appending a new content. So I checked at AngularJs and I was reusing the directive template. So basically create two directives for each template and voilá(Hated doing this). No more slow scroll.

Scroll on container changes speed on scrolling larger groing containers

It is possible to improve scrolling on a list with large number of containing objects.
<ul>
<li>text1</li>
<li>text2</li>
<li>text3</li>
<li>text4</li>
<li>...</li>
.
.
.
<li>text1000</li>
</ul>
Whenever I scroll over 90% of the elements in container, I make a js call that will load more results to my container and will add my rest of the elements to the ul.
Can I modify the scroll speed when scrolling based on the number of the results?
p.s. I don't have any code that I have tried on this situation. I don't know how to do this. This is the last attempt in order to solve a problem that I have.
p.s. 2 i would like a solution without any extra library than jquery or jqm.
Edit:
By modify the scroll speed I mean to change the scroll to go faster if there are many objects and slower otherwise

You can use this kind of snippet:
{Change timeout delay for less boring effect using scrollbar}
SEE DEMO
(function () {
var $ul = $('ul');
for (var i = 1; i < 1001; i++)
$ul.append('<li>test::' + i + '</li>');
var lastScrollTop = 0,
st,
direction;
function getDirection() {
st = window.pageYOffset;
if (st > lastScrollTop) {
direction = "down";
} else {
direction = "up";
}
lastScrollTop = st;
return direction;
}
var scrolling = function () {
var $window = $(this);
$window.off('scroll');
var delta = $ul.height() / 10,
scroll = $window.scrollTop();
if (getDirection() === "down") $window.scrollTop(delta + scroll);
else $window.scrollTop(scroll - delta);
console.log($(window).scrollTop());
lastScrollTop = this.pageYOffset;
setTimeout(function () {
$window.on('scroll', scrolling);
}, 0);
};
$(window).on('scroll', scrolling);
})();

parallax scrolling issue - div element jerking when scrolling in webkit browsers

I have created a parallax scroll, which seem to be working fine in firefox however in the chrome browser there's a slight jump on the body text when scrolling. click here scroll to the about section. I am not sure if t this is a css or JS issue.. below is a snippet i have incorporated into my parallax function
Does anyone know how i an fix this issue?
$(document).ready(function(){
// Cache the Window object
$window = $(window);
// Cache the Y offset and the speed of each sprite
$('[data-type]').each(function() {
$(this).data('offsetY', parseInt($(this).attr('data-offsetY')));
$(this).data('Xposition', $(this).attr('data-Xposition'));
$(this).data('speed', $(this).attr('data-speed'));
});
// For each element that has a data-type attribute
$('[data-type="background"]').each(function(){
// Store some variables based on where we are
var $self = $(this),
offsetCoords = $self.offset(),
topOffset = offsetCoords.top;
// When the window is scrolled...
$(window).scroll(function() {
// If this section is in view
if ( ($window.scrollTop() + $window.height()) > (topOffset) &&
( (topOffset + $self.height()) > $window.scrollTop() ) ) {
// Scroll the background at var speed
// the yPos is a negative value because we're scrolling it UP!
var yPos = -($window.scrollTop() / $self.data('speed'));
// If this element has a Y offset then add it on
if ($self.data('offsetY')) {
yPos += $self.data('offsetY');
}
// Put together our final background position
var coords = '50% '+ yPos + 'px';
// Move the background
$self.css({ backgroundPosition: coords });
$('[data-type="scroll-text"]', $self).each(function() {
var $text= $(this);
var pos = ($window.scrollTop()/10) * $text.data('speed');
var curP = $text.css('margin-top');
var is_chrome = navigator.userAgent.toLowerCase().indexOf('chrome') > -1;
if(is_chrome) {
$text.animate({
paddingTop: pos,
}, 200, 'linear', function() {
// Animation complete.
});
} else {
$text.css('padding-top', pos);
}
});
}; // in view
}); // window scroll
}); // each data-type
}); // document ready

Some suggestions:
1.) Use position: fixed to avoid any jitter, as you'll be taking the element out of the document flow. You can then position it using z-index.
2.) Cache as much as you can to ease processing time.
3.) Math.round may not be necessary, but try adding this CSS to your moving areas: -webkit-transform: translate3d(0,0,0); This will force hardware acceleration in Chrome, which may ease some of the jittering. (It looked smoother on my screen when I added this with Inspector, but it didn't get rid of the jumpiness with the scroll wheel.) Note: Don't do this on your entire document (e.g. body tag), as it might cause some issues with your current layout. (Your navigation bar didn't stick to the top of the window, for instance.)
4.) If you have any animations running as part of your parallax logic (tweening the margin into place or something along those lines), remove it - that would probably cause the jump you see.
Hope this helps. Best of luck.

I see the same jittering in FireFox and Chrome (Mac). Looking at your containers, one thing that's glaring at me is the pixel position that's being calculated/used.
Chrome: <div id="about-title" style="margin-top: 1562.3999999999999px;">
FireFox: <div id="about-title" style="margin-top: 1562.4px;">
Browsers aren't going to allow content to sit at 1/2 pixel, let alone 0.3999999 of a pixel. I think it's moving it, and trying to calculate whether to round up or round down. It jitters because it's calculating with every click of your mouse wheel.
Thus, I'd try adding Math.round() to your positions so that the containers are never being left in limbo.
Take a look at the code here: http://webdesigntutsplus.s3.amazonaws.com/tuts/338_parallax/src/index.html
Firebug some of the elements, and you'll see that their only fraction of a pixel is '0.5'. Most of them (the bulk) go to round number values.

You are going to have to change the way that the scrolling works (i.e. change how the spacing is computed), but this can be fixed by adding the position:fixed CSS element to the page elements that are scrolling. The problem is coming from the time that it takes for the JavaScript to process and then render.
For example, on your page you would set each of the <div> tags containing text to have a fixed position and then use the JavaScript/JQuery function to update the top: CSS element. This should make the page scroll smoothly.

Have you tried adding the preventdefault inside the scroll function?
$(window).scroll(function(e) {
e.preventDefault();
// rest of your code
}

In a previous question I created a fairly good parallax scrolling implementation. Jquery Parallax Scrolling effect - Multi directional You might find it useful.
Here's the JSFiddle http://jsfiddle.net/9R4hZ/40/ use the up/down arrows or scroll wheel.
Using padding and margin for the positioning are probably why you're experiencing rendering issues. While my code uses scroll or keyboard input for the effect you can loop the relavent portion and check the $moving variable until you reach the desired element on screen.
function parallaxScroll(scroll) {
// current moving object
var ml = $moving.position().left;
var mt = $moving.position().top;
var mw = $moving.width();
var mh = $moving.height();
// calc velocity
var fromTop = false;
var fromBottom = false;
var fromLeft = false;
var fromRight = false;
var vLeft = 0;
var vTop = 0;
if($moving.hasClass('from-top')) {
vTop = scroll;
fromTop = true;
} else if($moving.hasClass('from-bottom')) {
vTop = -scroll;
fromBottom = true;
} else if($moving.hasClass('from-left')) {
vLeft = scroll;
fromLeft = true;
} else if($moving.hasClass('from-right')) {
vLeft = -scroll;
fromRight = true;
}
// calc new position
var newLeft = ml + vLeft;
var newTop = mt + vTop;
// check bounds
var finished = false;
if(fromTop && (newTop > t || newTop + mh < t)) {
finished = true;
newTop = (scroll > 0 ? t : t - mh);
} else if(fromBottom && (newTop < t || newTop > h)) {
finished = true;
newTop = (scroll > 0 ? t : t + h);
} else if(fromLeft && (newLeft > l || newLeft + mw < l)) {
finished = true;
newLeft = (scroll > 0 ? l : l - mw);
} else if(fromRight && (newLeft < l || newLeft > w)) {
finished = true;
newLeft = (scroll > 0 ? l : l + w);
}
// set new position
$moving.css('left', newLeft);
$moving.css('top', newTop);
// if finished change moving object
if(finished) {
// get the next moving
if(scroll > 0) {
$moving = $moving.next('.parallax');
if($moving.length == 0)
$moving = $view.find('.parallax:last');
} else {
$moving = $moving.prev('.parallax');
if($moving.length == 0)
$moving = $view.find('.parallax:first');
}
}
// for debug
$('#direction').text(scroll + " " + l + "/" + t + " " + ml + "/" + mt + " " + finished + " " + $moving.text());
}

May not be related to your specifics, but I had a jumpy parallax scrolling problem, I was able to solve it adding the following CSS for the fixed portions of the page:
#supports (background-attachment: fixed)
{
.fixed-background
{
background-attachment: fixed;
}
}
Not sure of all the specifics, but found at Alternate Fixed & Scroll Backgrounds

Javascript fixed-top navbar only after scrolling

Does anyone know what javascript effects are being used to create the navbar effect on lesscss.org where the navbar only becomes fixed to the top after scrolling beyond a certain point. If anyone has actual code examples, or links to tutorials, that'd be appreciated.

it's a javascript check using the window.onscroll event
in the HTML source near the top:
window.onscroll = function () {
if (!docked && (menu.offsetTop - scrollTop() < 0)) {
menu.style.top = 0;
menu.style.position = 'fixed';
menu.className = 'docked';
docked = true;
} else if (docked && scrollTop() <= init) {
menu.style.position = 'absolute';
menu.style.top = init + 'px';
menu.className = menu.className.replace('docked', '');
docked = false;
}
};