Efficiently creating a simple parallax effect with jQuery - javascript

So for one of my new projects, I decided to write a super simple parallax script for some background images on scroll. This is what I came up with:
$(document).ready(function(){
parallaxScroll();
$(window).bind('scroll', function() {
parallaxScroll();
});
});
function parallaxScroll() {
$(".parallax").each(function() {
if($(this).hasClass('reverse')) {
$(this).css("background-position","center " + (($(this).offset().top - $(window).scrollTop())/2) + "px");
} else {
$(this).css("background-position","center " + (($(this).offset().top - $(window).scrollTop())/-2) + "px");
}
});
}
My question is, is this efficient enough? If not, is there a better solution? I wasn't sure if using an .each() would be best for performance, but it seems to work fine. The reason I have the function run at document load is so when you scroll the page for the first time, the background image doesn't jump.

Instead of css which sets the value immediately, consider using animate instead. It defers setting values using timers/requestAnimationFrame, ensuring that your animation does not block the UI, is async (runs pseudo-parallel to other code), and ensures that the animation is smooth.

This is a plain JS solution, but you'll be able to port it to jQuery really easily:
var lastScrollY = 0;
var backgroundImageY = 0;
var requestAnimationFrame = window.requestAnimationFrame ||
window.msRequestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.webkitRequestAnimationFrame;
window.addEventListener('load', processScrollEvent);
function processScrollEvent() {
var innerHeight = window.innerHeight;
var scrollHeight = document.body.scrollHeight;
var backgroundImage = document.querySelector('#background img');
lastScrollY = document.body.scrollTop;
var currBackgroundImageY = Math.round(((backgroundImage.scrollHeight - innerHeight) / 100) * ((lastScrollY / (innerHeight - scrollHeight)) * 100));
if(currBackgroundImageY != backgroundImageY) {
backgroundImageY = currBackgroundImageY;
requestAnimationFrame(processScrollAnimationFrame);
}
}
function processScrollAnimationFrame() {
var backgroundImage = document.querySelector('#background img');
var transforms = ['transform', 'oTransform', 'msTransform', 'mozTransform', 'webkitTransform'];
for(var i = 0; i < transforms.length; i++) {
backgroundImage.style[transforms[i]] = 'translate3d(0, ' + backgroundImageY + 'px, 0)';
}
}

Related

Remove function on browser width

I'm still very new to javascript and I'm learning as I build. This may be a simple fix but how would I disable a function on my parallax images ( or disable a specific js function in general ) on a smaller width?
Here's what I have so far that doesn't quite work but shows "undefined". I've been searching for a solution for a couple of days now with no luck. Any help would be appreciated.
var paraLlaxS = document.querySelector("#firstImgc2");
var paraLlaxS = document.querySelector("#secondImgc2");
var paraLlaxS = document.querySelector("#backbox1");
function setTranslate(xPos, yPos, el) {
el.style.transform = "translate3d(" + xPos + ", " + yPos + "px, 0)";
}
window.addEventListener("DOMContentLoaded", scrollLoop, false);
var xScrollPosition;
var yScrollPosition;
function scrollLoop() {
xScrollPosition = window.scrollX;
yScrollPosition = window.scrollY;
setTranslate(0, yScrollPosition * -0.2, firstImgc2);
setTranslate(0, yScrollPosition * 0.15, secondImgc2);
setTranslate(0, yScrollPosition * -0.6, backbox1);
requestAnimationFrame(scrollLoop);
if(window.innerWidth < 900) {
document.querySelector('#firstImgc2').innerHTML = window.removeEventListener("DOMContentLoaded", scrollLoop, false);
return;
} else {
}
}
You could add a conditional return at the beginning of you function. But if the width increases again you would need to listen for that to start the loop again.
function scrollLoop() {
if(window.innerWidth < 900)return;
...
I borrowed a solution from another post.
Listen for browser width for responsive web design?
This code is compatible with a wider variety of browsers as getting the screen size can vary depending on the browser.
var width = 0;
function getWindowSize() {
if (document.body && document.body.offsetWidth) {
width = document.body.offsetWidth;
}
if (document.compatMode=='CSS1Compat' &&
document.documentElement &&
document.documentElement.offsetWidth ) {
width = document.documentElement.offsetWidth;
}
if (window.innerWidth) {
width = window.innerWidth;
}
return(width);
}

Slow Scroll jittery

I am using this code: EXAMPLE
Depending on if "image-ul" is fully above the bottom edge of the browser window or not, will make divs scroll at different speeds, as it should. But the problem that I am having is that the scrolling is not smooth when the slow scrolling divs get somewhere close to the top of the page. They seem to stall for a moment, and even scroll in the opposite direction sometimes.
//
// default speed ist the lowest valid scroll speed.
//
var default_speed = 1;
//
// speed increments defines the increase/decrease of the acceleration
// between current scroll speed and data-scroll-speed
//
var speed_increment = 0.01;
//
// maximum scroll speed of the elements
//
var data_scroll_speed_a = 3; // #sloganenglish
var data_scroll_speed_b = 5; // #image-ul
//
//
//
var increase_speed, decrease_speed, target_speed, current_speed, speed_increments;
$(document).ready(function() {
$(window).on('load resize scroll', function() {
var WindowScrollTop = $(this).scrollTop(),
Div_one_top = $('#image-ul').offset().top,
Div_one_height = $('#image-ul').outerHeight(true),
Window_height = $(this).outerHeight(true);
if (WindowScrollTop + Window_height >= (Div_one_top + Div_one_height)) {
$('#sloganenglish').attr('data-scroll-speed', data_scroll_speed_a).attr('data-current-scroll-speed', default_speed).attr('data-speed-increments', data_scroll_speed_a * speed_increment);
$('#image-ul').attr('data-scroll-speed', data_scroll_speed_b).attr('data-current-scroll-speed', default_speed).attr('data-speed-increments', data_scroll_speed_b * speed_increment);
$('.slogan-a-line').css('color', 'yellow');
increase_speed = true;
decrease_speed = false;
} else {
$('#sloganenglish').attr('data-scroll-speed', '1').attr('data-current-scroll-speed', default_speed);
$('#image-ul').attr('data-scroll-speed', '1').attr('data-current-scroll-speed', default_speed);
$('.slogan-a-line').css('color', 'red');
decrease_speed = true;
increase_speed = false;
}
}).scroll();
});
// data-scroll-speed script
$.fn.moveIt = function() {
var $window = $(window);
var instances = [];
$(this).each(function() {
instances.push(new moveItItem($(this)));
});
window.onscroll = function() {
var scrollTop = $window.scrollTop();
instances.forEach(function(inst) {
inst.update(scrollTop);
});
}
}
var moveItItem = function(el) {
this.el = $(el);
this.speed = parseInt(this.el.attr('data-scroll-speed'));
this.current_speed = 1.0;
};
moveItItem.prototype.update = function(scrollTop) {
target_speed = parseInt(this.el.attr('data-scroll-speed'));
current_speed = this.current_speed;
speed_increments = parseFloat(this.el.attr('data-speed-increments'));
if (increase_speed) {
if (current_speed < target_speed) {
current_speed += speed_increments;
} else {
current_speed = target_speed;
}
} else if (decrease_speed) {
if (current_speed > default_speed) {
current_speed -= speed_increments;
}
if ($(window).scrollTop() === 0) {
current_speed = default_speed;
}
}
this.current_speed = current_speed;
var pos = scrollTop / this.current_speed;
this.el.css('transform', 'translateY(' + -pos + 'px)');
};
// Initialization
$(function() {
$('[data-scroll-speed]').moveIt();
});
The sample code wasn't slow for me, so it may be specific to your machine or browser.
However, there are a few things you can do:
Don't use jQuery where you don't need it. jQuery is significantly slower than using native JS functions (e.g. document.getElementById).
Don't repeatedly use jQuery selectors. Every time you use a jQuery selector, you suffer a performance hit. So for example, instead of this:
function(){
var Div_one_top = $('#image-ul').offset().top,
Div_one_height = $('#image-ul').outerHeight(true);
}
Do this:
var imageUl = $('#image-ul');
function(){
imageUl.offset().top,
imageUl.outerHeight(true);
}
This example should increase performance quite a bit. You're doing multiple jQuery selectors every time the page scrolls for no reason.
The best choice for something performance intensive is to cut out jQuery completely and do it by hand.

Javascript animation with variable speed based on cursors position

What I want to achieve is a javascript animation with variable speed based on cursor position.
For that porpouse I'm using jquery's animate function and mousever event and javascript's setInterval function, but those aren't required, so if there is a better way to achieve it I would be more than happy to hear it (the only requeriment would be javascript).
The problem I'm facing is that I can't change speed dinamicly, for some reason the speed keeps adding to the one it already had instead of set what I wanted and even if it would change as spected it just doesn't happen in a smoothly way because of an unknown reason for me.
Here is the javascript that I have so far:
//settings for container_slider. Are used in startSlider() which handles the animation
var steps_animation_speed = 1000;
var steps_interval = 1500;
var steps_speed_factor = 1; // 100%
var amount_sliders = 3;
//cache DOM elements
var $container_slider = $('#container_slider');
var $shown_slides = $('.shown_slides', $container_slider);
var $slide = $(".slide");
// Just making sure sizing (widths) fits as they should.
var slides_width = $container_slider.width()/amount_sliders;
var slides_margin = parseInt($slide.css('marginLeft').replace('px', '')) + parseInt($slide.css('marginRight').replace('px', ''));
var steps_width = slides_width + slides_margin;
$shown_slides.css('width', steps_width*(amount_sliders+1) + 'px');
$slide.css('width', slides_width);
var interval;
// This function is responsible of the animation
function startSlider() {
$shown_slides.stop(false);
interval = setInterval(function() {
$shown_slides.animate({'margin-left': '-='+steps_width}, steps_animation_speed*steps_speed_factor, function() {
$('.shown_slides > li:last').after($('.shown_slides > li:first'));
$('.shown_slides').css('margin-left', '0');
});
}, steps_interval);
}
function pauseSlider() {
clearInterval(interval);
}
$container_slider.mouseleave(function(){
steps_interval = 3000;
$shown_slides.stop(true);
pauseSlider();
startSlider();
});
// $container_slider.mouseenter(function(){
// pauseSlider();
// });
$container_slider.mousemove(function(event){
pauseSlider();
var cursor_location = '';
if(event.pageX > 0 && event.pageX < 165){
cursor_location = "Cursor is on the left side";
// This is where i'm doing the tests that should work of changing animation's speed based on cursor position
if(steps_speed_factor !== (event.pageX / 165)){
steps_speed_factor = event.pageX / 165;
steps_speed_factor = (steps_speed_factor < 0.15 ? 0.15 : steps_speed_factor);
steps_interval = 0;
startSlider();
}
} else if(event.pageX > 165 && event.pageX < ($container_slider.width()-165)){
cursor_location = "Cursor is in the center (paused)";
// This stops animation, it could be achieved way better but i'm focusing on above's block of code.
steps_speed_factor = 1;
steps_interval = 3000;
$shown_slides.stop(true);
pauseSlider();
} else if(event.pageX > ($container_slider.width()-165) && event.pageX < $container_slider.width()) {
cursor_location = "Cursor is on the right side";
// This would be an exact copy (almost) of the left side, but since it doesn't work yet, this is pretty much a "blank" block of code
steps_interval = 0;
steps_speed_factor = ( event.pageX - ($container_slider.width() - 165) ) / 165;
}
$(".coordinates").html("X: " + event.pageX + " Y: " + event.pageY );
$(".cursor_location").html(cursor_location);
$(".speed_factor").html("Speed Factor is: "+steps_speed_factor);
});
startSlider();
Here is a codepen showing this javascript code "working".
--- EDIT
I forgot to explain propperly what happens in the codepen , since it is just an example didnt give it to much importance. Mainly what should happen is that the furthier the cursor is from the center, the tinier/faster the invervals of the animation should be without losing fluidness.
In this case i'm using a "speed factor" which I calculate by taking cursor's X position and then comparing it with a predefined area, converting it in a percentage (decimal) from 15% to 99%. But it isn't actually the important part. I'm clueless about how to achieve this and the more I try the messier my code gets, so as long as you can give me an example of changing animation's speed (in "real" time, i mean, smoothly/fluid) based on cursor's position as an example it would be perfect.

How I can move DOM elements slowly?

How I can move DOM elements slowly?
This does not work
for ( var a = 0 ; a < 100 ; a++){
$('*').each(function(){
if ( ! /HTML/.test($(this).context.nodeName))
{
var top = parseInt($(this).css('top')) + 1;
$(this).css('top',top + "px");
}
});
}
Elements are positioned when the loop finish
How can I do this slowly?
Sorry for my English
Or in pure javascript, you should use a timer
var $elem = $(this), // jquery object
elem = $elem[0], // dom element
currentPos = $elem.offset().top, // current position
targetPos = currentPosition + 100, // target position
timer = setInterval (function () { // timer to move element slowly
currentPos++;
$elem.css('top',currentPosition + "px");
if (currentPos == targetPos)
clearInterval(timer);
}, 100);
try jquery's $.animate()
it requires you to set a target position to move to, rather than continuous movement
or using setInterval:
intervalInMilliseconds=17;//60 frames per second
var interval = setInterval(function()
{
for ( var a = 0 ; a < 100 ; a++){
$('*').each(function(){
if ( ! /HTML/.test($(this).context.nodeName))
{
var top = parseInt($(this).css('top')) + 1;
$(this).css('top',top + "px");
}
});
}
},intervalInMilliseconds);
stop when you're done by doing this:
clearInterval(interval)
If you are targetting new enough browser versions, you could use CSS animation instead.

JS/jQuery delay loop to get desire result (delay() not working)

I'm trying to create an loading icon by moving the css 'background-position' of an image in a loop:
$('#LoginButton').click(function () {
var i = 1, h = 0, top;
for (i = 0; i <= 12; i++) {
h = i * 40;
top = h + 'px';
$('#ajaxLoading').css('background-position', '0 -' + top).delay(800);
}
});
The problem here is that it runs to fast so I don't se the 'animation' of the moving background.
So I added jquerys delay(), but:
delay(800) is not working because delay() only works in jquery animation effects and .css() is not one of those.
How to delay this loop?
I'd suggest using jQuery timer plugin: http://jquery.offput.ca/js/jquery.timers.js
$('#LoginButton').click(function () {
var times = 13;
var delay = 300;
var h = 0, top;
$(document).everyTime(delay, function(i) {
top = h + 'px';
$('#ajaxLoading').css('background-position', '0 -' + top);
h += 40;
}, times);
});
In case you don't want any plugins, use setInterva/clearInterval:
$('#LoginButton').click(function () {
var delay = 300;
var times = 13;
var i = 0, h = 0, top;
doMove = function() {
top = h + 'px';
$('#ajaxLoading').css('background-position', '0 -' + top);
h += 40;
++i;
if( i >= times ) {
clearInterval( interval ) ;
}
}
var interval = setInterval ( "doMove()", delay );
});
Have you looked at using animate() instead of css()? I'm not 100% sure I understand what you're trying to accomplish, so this is kinda a shot in the dark.
http://api.jquery.com/animate/
Chrome, Safari and IE3+ should support background-position-y, so if you're targeting these specific browser, using jquery you could just make a timed animation() on backgroundPositionY property - http://snook.ca/archives/html_and_css/background-position-x-y
(On Firefox the effect won't work)
You can use setTimeout() and clearTimeout() functions in order to accomplish that.
IE:
var GLOBAL_i = 0;
function doAnimation() {
var h = GLOBAL_i * 40;
var top = h + 'px';
$('#ajaxLoading').css('background-position', '0 -' + top);
if (GLOBAL_i < 12) {
GLOBAL_i++;
t=setTimeout(doAnimation, 800);
}
}
$('#LoginButton').click(function () {
doAnimation()
});

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