Custom scrollbar logic

Question

I made a custom div scroller based on TweenMax easings and jQuery mousewheel events. The scroll works like a charm but I need to move the scrollbar handler to show the scroll progress. I made some tests based on calcs of parent width, scrollLeft and total div width, but didn't found the right solution…
I tried to adapt this example for my horizontal scrollbar, but it's still a strange behaviour.
Any idea?

$(window).on("mousewheel DOMMouseScroll", function (e) {
    e.preventDefault();
    var delta = e.originalEvent.wheelDelta / 120 /* Chrome */ || -e.originalEvent.detail; /* FF */
    var dur = 1.2;
    TweenLite.to($("#photos"), dur, {
        scrollLeft: $("#photos").scrollLeft() - parseInt(delta * 35),
        ease: Expo.easeOut,
        overwrite: 5
    });
});

Live example:
http://jsfiddle.net/tccsq6e9/2/

Your `handle` has width 12%. why? The width should match the right ratio and should be also calculated on window resize since than the scrollWidth of the #photos changes. — Roko C. Buljan, Jan 25 '15 at 20:02
@RokoC.Buljan absolutely not, the 12% is only a styling choice. I just want to move that scrollbar handler. — flks, Jan 25 '15 at 20:04
Ohh, got it so it'll always be "fixed" at 12% width. Any way, on window resize you'll need to re-calculate the handler width and the area scrollwidth ratio to make it always arrive at the far scrollbar-end when the #photos gets to it's far-scroll-end. — Roko C. Buljan, Jan 25 '15 at 20:14
@RokoC.Buljan that's it! / Didn't kept. That was not working and very buggy… :/ — flks, Jan 25 '15 at 20:25
@RokoC.Buljan got it back from a Time Machine backup: http://jsfiddle.net/tccsq6e9/3/ — as you can see, that's a lot of calcs and there is no limit on edges. I found that code on an [online example](http://istockphp.com/demo/how-to-create-jquery-scrollbar-div/) for a vertical scrollbar. — flks, Jan 25 '15 at 20:53

Roko C. Buljan · Accepted Answer · 2022-10-21T16:47:05.993

Scrollbars math logic

Scrollbars logic:

(onInit, onResize) thumbSize = viewportSize * viewportSize / areaSize
(onThumbDrag)      viewportScrollPos = areaSize / viewportSize * thumbPos
(onViewportScroll) thumbPos = viewportScrollPos / viewportSize * thumbSize

That's it. Get the math on scroll but also on window resize to make the handler act like a real scrollbar would:

Here's the final result with simplified CSS, HTML and JS

var $gallery   = $("#thumbs"),
    $scrollbar = $("#scrollbar"),
    $handler   = $("#scrollbar-handle"),
    galleryAvailScroll = 0,
    handlerAvailScroll = 0,
    handlerLeft = 0;

function setPos() {
  galleryAvailScroll = $gallery[0].scrollWidth - $gallery.outerWidth(true); // PX
  handlerAvailScroll = $scrollbar.width() - $handler.width(); // PX
  handlerLeft = $gallery.scrollLeft() * handlerAvailScroll / galleryAvailScroll;
  $handler.css({left: handlerLeft});
}
setPos(); // Get the sizes
$(window).on("resize", setPos); // Also on resize

// Scroll
$gallery.on("mousewheel DOMMouseScroll", function (e) {
  e.preventDefault();
  var eorg  = e.originalEvent,
      delta = eorg.wheelDelta/120 || -eorg.detail; // Ch || FF
  
  TweenLite.to( $gallery, 0.7, {
    scrollLeft : $gallery.scrollLeft() - delta * 35,
    ease : Expo.easeOut,
    overwrite : 5,
    onUpdate : setPos
  });
  
});

body {
  padding: 15px 0 0;
  margin: 0;
}
#thumbs {
  position:relative;
  overflow:hidden;
  padding:0 10px;
  height: 175px;
  white-space: nowrap;
}
#thumbs > div {
  font-size:16px;
  display:inline-block;
  width: 150px; height: 150px;
  margin: 0 6px; /*6 + 4 LineWidth = 10 */
  background:#000;
}
#scrollbar {
  margin:0 70px;
  height:3px;
  position:relative;
  background:#ddd;
}
#scrollbar-handle {
  position:absolute;
  width:12%;
  left:0;
  height:3px;
  background:red;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="http://cdnjs.cloudflare.com/ajax/libs/gsap/latest/TweenMax.min.js"></script>
<div id="thumbs">
  <div></div>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
</div>

<div id="scrollbar">
  <span id="scrollbar-handle"></span>
</div>

Since your handler is "fixed" at 12% width, if you decide to make it's width content-related, you can get the needed math from How to make custom scrollbar jQuery plugin

Dang, you're the man! Didn't know that was possible to use that onUpdate callback to move the scrollbar indicator. Thank you so much for your help :) — flks, Jan 26 '15 at 09:16
I just adapted the code in my actual design, that works like a charm. But I have a simple question: why when I write `onUpdate: setPos()`, it works but move bumpy? `onUpdate: setPos` works well. Is `setPos()` considered as a function and `setPos` as a variable? Or something like that? — flks, Jan 26 '15 at 19:02
@flks http://stackoverflow.com/questions/3246928/in-javascript-does-it-make-a-difference-if-i-call-a-function-with-parentheses — Roko C. Buljan, Jan 26 '15 at 20:11
@flks (if the answers there were a bit confusing) The Method `onUpdate` accepts a **function**: `onUpdate : function(){ /*code here*/ }`, so we use it like `onUpdate : setPos` so by *Assigning* that Method (property)> our function. If instead you wrote `onUpdate : setPos()` would be pretty much the same as *Executing immediately that function* (instead of assigning) like: `onUpdate : (function(){ /*execute!*/ }())` which is not what we need and what the callback is there made for.. — Roko C. Buljan, Jan 26 '15 at 20:35

Custom scrollbar logic

1 Answers1

Scrollbars math logic