Using Javascript for Background Image Change on Page Refresh - Responsive? - javascript

I am new to javascript, but I am currently using javascript in my head tag that changes images randomly on page refresh. This has been working great. The javascript can be seen below.
<script type="text/javascript">
function changeImg(imgNumber) {
var myImages = ["image1.jpg", "image2.jpg", "image3.jpg", "image4.jpg"];
var imgShown = document.body.style.backgroundImage;
var newImgNumber =Math.floor(Math.random()*myImages.length);
document.body.style.backgroundImage = 'url('+myImages[newImgNumber]+')';
}
window.onload=changeImg;
Now I want to take it one step further and make the images responsive. I've tried a number of different tags via media queries, but nothing seems to work 100%. This particular page has a top section with a height of 310px, which is also where the images are displayed - they also have a height of 310px. Is this something I can do with CSS or CSS3? Or will I need to add additional javascript?
Thanks for the help in advance... my brain hurts!

Related

Skrollr Image Flicker. Firefox preload issue

Im in the process of developing a 'flipbook-style' animation using Skrollr by triggering background image changes when the user scrolls to indicated positions on the page. The issue i'm having is that in browser the image changes are delayed, creating what can only be defined as a 'flicker' of white between the frames.
<div class="section" style="background: url('frame1.png')"
data-560-top="background-image:!url('frame1.png');"
data-440-top="background-image:!url('frame2.png');">
The HTML is simple; it basically states that at 560 pixels from the top of the div (in relation to the browser window), the background should be at frame 1, then as the user scrolls closer to the div (440 pixels from the top of the div) the background image changes to frame 2. I plan to use up to around 20 frames and the images are quite large.
I have created a JSBin here which includes a very simplified sample with images from placehold.it. This includes the Skrollr script and an example layout of a section of my project. The key difference being that the images in my project are of much larger scale.
(function($) {
var cache = [];
// Arguments are image paths relative to the current page.
$.preLoadImages = function() {
var args_len = arguments.length;
for (var i = args_len; i--;) {
var cacheImage = document.createElement('img');
cacheImage.src = arguments[i];
cache.push(cacheImage);
}
};
})(jQuery);
jQuery.preLoadImages(
'http://www.placehold.it/300x200.png',
'http://www.placehold.it/300x200.png'
);
The above snippet seems to be working on Chrome, however the flicker issue remains in Firefox. Based on research, firefox handles cached images differently from Chrome? (e.g Where an image is not considered needed by firefox at a given time, it is trashed?)
I would like to know how I could possibly force all browsers to preload the images efficiently, to potentially avoid the background image flicker upon change. I am still quite new to Javascript/JQuery.
I hope I have provided a clear explanation. All assistance appreciated.
Dan
You can preload images using CSS only, no need for JS. Check out this article for more info. Another interesting way to do it is in the comment section of the article. Basically you assign the background image to a pseudo-element so that is is cached and ready to be used whenever. See this code for an example:
#something:before {
content: url("./img.jpg");
width:0;
height:0;
visibility:hidden;
}

How to apply blur effect to background image in Blogger?

I've been trying to add blur effect to my posts but only thing that gets blurred is the main post content (pic: http://i.gyazo.com/9d94d2be5dc3f3ada982564aa212336e.jpg). Any idea how to target the background-image, instead of the content?
The code I am using at the moment is:
<script type="text/javascript">
var image = document.querySelector('.post-body img').src;
var target = document.body;
target.style.backgroundImage = "url(" + image + ")";
target.style.backgroundSize = "cover";
document.body.style["background-attachment"] = "fixed";
</script>
I have a odd feeling that you need to make the actual background image into standalone element but I have no idea how.
Also, is there a possibility I could add Blur.js into blogger or is it only for Wordpress? If yes, I'd like to know how?
Thanks in advance.
I worked on this and saw this question. So here's a suggestion.
<script type="text/javascript">
function showBackground() {
document.getElementsByClassName('body-fauxcolumn-outer')[0].style.backgroundImage = "url('http://backgroundImage.jpg')";
document.getElementsByClassName('body-fauxcolumn-outer')[0].style.backgroundPosition = "center center";
document.getElementsByClassName('body-fauxcolumn-outer')[0].style.backgroundRepeat = "no-repeat";
document.getElementsByClassName('body-fauxcolumn-outer')[0].style.backgroundAttachment = "fixed";
document.getElementsByClassName('body-fauxcolumn-outer')[0].style.webkitFilter = "blur(5px)";
}
window.onload = showBackground();
</script>
Explanation
As I used the simple template at this time, I noticed that the standard template has a class named body-fauxcolumn-outer which is used to set the background color.
So I adapt my answer here to answer this question.
I just added the following to fix the blur as you can see in the image bellow.
document.getElementsByClassName('body-fauxcolumn-outer')[0].style.webkitFilter = "blur(15px)";
You could try use this CSS 3 tag:
filter: blur(5px);
You can see the mdn documentation here: https://developer.mozilla.org/en-US/docs/Web/CSS/filter
You can do this on Blogger without using any JS or CSS.
Upload your image into a Blogger post as if you want to put it in an article.
Copy the URL of the image and paste it into the body css like so:
body {
background-image: url('YOUR IMAGE URL HERE');
}
Replace the /s-1600/ part of the url with /s1600-fcrop64=1,000f0000ffceffff:Soften=1,20,0/
Note: You can adjust the radius of the blur by fiddling with the second number after Soften=(in the case above, 20).
The advantage of doing this is it's lighter on code and completely compatible with every device and browser that is capable of loading an image!

conditional changing the source and dimentions of video in javascript

I have this code below:
<script type="text/javascript">
jwplayer("container").setup({
flashplayer: "http://test.captive-portal.com/jwplayer/player.swf",
file: "http://content.captive-portal.com/files/video/cirque-du-soleil/mob.mp4",
image: "http://content.captive-portal.com/files/video/cirque-du-soleil/mob.jpg",
height: 285,
width: 480,
});
</script>
The whole page is here (in case you need it): video page.
What I'm trying to do is to change the 4 lines: file: (...), image (...), height(...) and width (...) depending of the resolution of the window. I have managed to do this with css, so styles are applied correctly, but this is javascript and I don't really know how to modify it. I was trying to place 2 similar scripts on one page in divs and hide the small one in case of big screen or hide a big one in case of small screen but it didn't work. Video didn't play. I think this may be caused by some scripts in the flash player file.
Is there any way to set conditions for those 4 lines depending of the screen resolution?
Thank you very much for your help in advance.
Those parameters are simply an object.
So you should be able to create that object out of the jwplayer call, and simply pass it in. e.g
var params = {};
params.flashplayer = "http://test.captive-portal.com/jwplayer/player.swf";
if(!mobile){ //you need to handle checking for mobile devices
params.file = "http://content.captive-portal.com/files/video/cirque-du-soleil/desktop.mp4";
params.image = "http://content.captive-portal.com/files/video/cirque-du-soleil/desktop.jpg";
params.height = 570;
params.width = 960;
}else{
//set params in same way but with mobile settings
}
jwplayer("container").setup(params);
If you later want to just resize the player. JwPlayer has a 'resize' function that you can call: jwplayer.resize(width,height)

Will this actually reload images?

I've written this simple image preloader based on my knowledge of javascript, but I don't know if it will actually load the images before the page is displayed or if it will still load the images.
function preloadImages(html) {
for(var i=0;i<document.images.length;i++) {
img_obj = new Image();
img_obj.src = document.images[i].src;
if (!img_obj.complete) alert("could not load:" + img_obj.src);
else continue;
}
$("#pad").fadeIn(200);
return true;
}
In addition, is it correct the way I preload the images?
To load the image the image needs to have a height/width on the page.
I think most people commonly insert the image into DOM, setting a height, width, making sure display is block. Set an absolute position at -9999px left and top, or something along those lines. The images will be cached for when you need them.
Depending on what you want to do. The js should run onload which is after the page has loaded so I am not sure you really get any benefit. (http://dean.edwards.name/weblog/2005/02/order-of-events/)
You can do preloading using CSS.

iPad/iPhone browser crashing when loading images in Javascript

I'm trying to build an image gallery in Safari that mimics the iPad photo app. It works perfectly, except that once I load more than 6MB or so worth of images either by adding them to the DOM or creating new Image objects, new images either stop loading or the browser crashes. This problem is widespread enough (with everyone else hitting up against the same limit) that I've ruled out my Javascript code as the culprit.
Given that you can stream much more than a few MB in a element or through the in-browser media player, this limit seems unnecessary, and there should be some kind of workaround available. Perhaps by freeing up memory or something else.
I also came across this reference for UIWebView.
"JavaScript allocations are also limited to 10 MB. Safari raises an exception if you exceed this limit on the total memory allocation for JavaScript."
Which matches what I'm seeing fairly well. Is it possible to deallocate objects in Javascript, or does Safari/UIWebView keep a running total and never lets go? Alternately, is there any workaround to load in data another way that doesn't eat up this 10MB?
Update: I think there's an even easier way to do this, depending on your application. Instead of having multiple images, if you simply have one <img> element or Image object (or maybe two, like a 'this' image and a 'next' image if you need animations or transitions) and simply update the .src, .width, .height and so on, you should never get near the 10MB limit. If you wanted to do a carousel application, you'd have to use smaller placeholders first. You might find this technique might be easier to implement.
I think I may actually have found a work-around to this.
Basically, you'll need to do some deeper image management and explicitly shrink any image you don't need. You'd normally do this by using document.removeChild(divMyImageContainer) or $("myimagecontainer").empty() or what have you, but on Mobile Safari this does absolutely nothing; the browser simply never deallocates the memory.
Instead, you need to update the image itself so it takes up very little memory; and you can do that by changing the image's src attribute. The quickest way I know of to do that is to use a data URL. So instead of saying this:
myImage.src="/path/to/image.png"
...say this instead:
myImage.src="data:image/gif;base64,AN_ENCODED_IMAGE_DATA_STRING"
Below is a test to demonstrate it working. In my tests, my large 750KB image would eventually kill the browser and halt all JS exectution. But after resetting src, I"ve been able to load in instances of the image over 170 times. An explanation of how the code works is below as well.
var strImagePath = "http://path/to/your/gigantic/image.jpg";
var arrImages = [];
var imgActiveImage = null
var strNullImage = "data:image/gif;base64,R0lGODlhEAAOALMAAOazToeHh0tLS/7LZv/0jvb29t/f3//Ub//ge8WSLf/rhf/3kdbW1mxsbP//mf///yH5BAAAAAAALAAAAAAQAA4AAARe8L1Ekyky67QZ1hLnjM5UUde0ECwLJoExKcppV0aCcGCmTIHEIUEqjgaORCMxIC6e0CcguWw6aFjsVMkkIr7g77ZKPJjPZqIyd7sJAgVGoEGv2xsBxqNgYPj/gAwXEQA7";
var intTimesViewed = 1;
var divCounter = document.createElement('h1');
document.body.appendChild(divCounter);
var shrinkImages = function() {
var imgStoredImage;
for (var i = arrImages.length - 1; i >= 0; i--) {
imgStoredImage = arrImages[i];
if (imgStoredImage !== imgActiveImage) {
imgStoredImage.src = strNullImage;
}
}
};
var waitAndReload = function() {
this.onload = null;
setTimeout(loadNextImage,2500);
};
var loadNextImage = function() {
var imgImage = new Image();
imgImage.onload = waitAndReload;
document.body.appendChild(imgImage);
imgImage.src = strImagePath + "?" + (Math.random() * 9007199254740992);
imgActiveImage = imgImage;
shrinkImages()
arrImages.push(imgImage);
divCounter.innerHTML = intTimesViewed++;
};
loadNextImage()
This code was written to test my solution, so you'll have to figure out how to apply it to your own code. The code comes in three parts, which I will explain below, but the only really important part is imgStoredImage.src = strNullImage;
loadNextImage() simply loads a new image and calls shrinkImages(). It also assigns an onload event which is used to begin the process of loading another image (bug: I should be clearing this event later, but I'm not).
waitAndReload() is only here to allow the image time to show up on the screen. Mobile Safari is pretty slow and displaying big images, so it needs time after the image has loaded to paint the screen.
shrinkImages() goes through all previously loaded images (except the active one) and changes the .src to the dataurl address.
I'm using a file-folder image for the dataurl here (it was the first dataurl image I could find). I'm using it simply so you can see the script working. You'll probably want to use a transparent gif instead, so use this data url string instead: data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==
The 6.5MB(iPad) / 10MB(iPhone) download limits are calculated based on the number of image elements used to set an image through its src property. Mobile safari doesn't seem to differentiate images loaded from cache or via the network. It also doesn't matter whether the image is injected into the dom or not.
The second part to the solution is that mobile safari seems to be able to load an unlimited number of images via the "background-image" css property.
This proof of concept uses a pool of precacher's which set the background-image properties once successfully downloaded. I know that it's not optimal and doesn't return the used Image downloader to the pool but i'm sure you get the idea :)
The idea is adapted from Rob Laplaca's original canvas workaround http://roblaplaca.com/blog/2010/05/05/ipad-safari-image-limit-workaround/
<!DOCTYPE html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>iPad maximum number of images test</title>
<script type="text/javascript">
var precache = [
new Image(),
new Image(),
new Image(),
new Image()
];
function setImage(precache, item, waiting) {
precache.onload = function () {
item.img.style.backgroundImage = 'url(' + item.url + ')';
if (waiting.length > 0) {
setImage(precache, waiting.shift(), waiting);
}
};
precache.src = item.url;
}
window.onload = function () {
var total = 50,
url = 'http://www.roblaplaca.com/examples/ipadImageLoading/1500.jpg',
queue = [],
versionUrl,
imageSize = 0.5,
mb,
img;
for (var i = 0; i < total; i++) {
mb = document.createElement('div');
mb.innerHTML = ((i + 1) * imageSize) + 'mb';
mb.style.fontSize = '2em';
mb.style.fontWeight = 'bold';
img = new Image();
img.width = 1000;
img.height = 730;
img.style.width = '1000px';
img.style.height = '730px';
img.style.display = 'block';
document.body.appendChild(mb);
document.body.appendChild(img);
queue.push({
img: img,
url: url + '?ver=' + (i + +new Date())
});
}
//
for (var p = 0; p < precache.length; p++) {
if (queue.length > 0) {
setImage(precache[p], queue.shift(), queue);
}
}
};
</script>
</head>
<body>
<p>Loading (roughly half MB) images with the <strong>img tag</strong></p>
</body>
</html>
So far I've had luck using <div> tags instead of <img> tags and setting the image as the div's background-image.
All in all, it's crazy. If the user is making an affirmative request for more image content, then there's no reason why Safari shouldn't allow you to load it.
I've had luck starting with the suggestion of Steve Simitzis, and Andrew.
My project:
PhoneGap-based app with 6 main sections, and about 45 subsections which have a jquery cycle gallery of between 2 and 7 images, each 640 x 440 (215+ images altogether). At first I was using ajax to load page fragments, but I've since switched to a one-page site, with all sections hidden until needed.
Initially, after going through about 20 galleries, I was getting memory warning 1, then 2, then the crash.
After making all the images into divs with the image applied as a background, I could get through more galleries (about 35) in the app before a crash, but after going to previously visited galleries, it would eventually fail.
The solution that seems to be working for me, is to store the background image URL in the div's title attribute, and setting all of the background images to be a blank gif. With 215+ images, I wanted to keep the url someplace in the html for sake of ease and quick reference.
When a subnavigation button is pressed, I rewrite the css background image to the correct source which is contained in the div's title tag, for ONLY the gallery that is showing. This saved me from having to do any fancy javascript to store the correct source image.
var newUrl = $(this).attr('title');
$(this).css('background-image', 'url('+newUrl+')');
When a new subnavigation button is pressed, I rewrite the background image of the last gallery divs to be blank gifs. So, aside from interface gfx, I only have 2-7 images 'active' at all times. With anything else I add that contains images, I just use this "ondemand" technique to swap the title with the background-image.
Now it seems I can use the app indefinitely with no crashes. Don't know if this will help anyone else, and it may not be the most elegant solution, but it provided a fix for me.
On a rails app, I was lazy loading hundreds of mid-size photos (infinite scroll) and inevitably hit the 10Mb limit on the iphone. I tried loading the graphics into a canvas (new Image, src=, then Image.onload) but still hit the same limit. I also tried replacing the img src and removing it (when it went out of viewable area) but still no cigar. In the end, switching out all the img tags w/ div's w/ the photo as background did the trick.
$.ajax({
url:"/listings/"+id+"/big",
async:true,
cache:true,
success:function(data, textStatus, XMLHttpRequest) {
// detect iOS
if (navigator.userAgent.match(/iPhone/i) || navigator.userAgent.match(/iPod/i) || navigator.userAgent.match(/iPad/i)) {
// load html into data
data = $(data);
// replace img w/ div w/ css bg
data.find(".images img").each(function() {
var src = $(this).attr("src").replace(/\s/g,"%20");
var div = $("<div>");
div.css({width:"432px",height:"288px",background:"transparent url("+src+") no-repeat"});
$(this).parent().append(div);
$(this).remove();
});
// remove graphic w/ dynamic dimensions
data.find(".logo").remove();
}
// append element to the page
page.append(data);
}
});
I can now load well over 40Mb of photos on one page w/o hitting the wall. I encountered an odd issue, though, with some of the css background graphics failing to show up. A quick js thread fixed that. Set the div's css bg property every 3 sec's.
setInterval(function() {
$(".big_box .images div.img").each(function() {
$(this).css({background:$(this).css("background")});
});
}, 3000);
You can see this in action at http://fotodeck.com. Check it out on your iphone/ipad.
I was unable to find a solution for this. Here are a couple of methods I tried, and all of them failed:
Simply changed the background of a DIV using div.style.backgroundImage = "url("+base64+")"
Changed the .src of an image using img.src = base64
Removed the old and added the new image using removeChild( document.getElementById("img") ); document.body.appendChild( newImg )
The same as above but with a random height on the new image
Removing and adding the image as a HTML5 canvas object. Also doesn't work, since a new Image(); has to be created, see *
On launch, created a new Image() object, let's call it container. Displayed the image as <canvas>, every time the image changed, I would change container's .src and redraw the canvas using ctx.drawImage( container, 0,0 ).
The sames as the previous, but without actually redrawing the canvas. Simply changing the Image() object's src uses up memory.
A strange thing I noticed: The bug occurs even if the image isn't displayed! For example, when doing this:
var newImg = new Image( 1024, 750 );
newImg.src = newString; // A long base64 string
Every 5 seconds, and nothing else, no loading or displaying the image, of course wrapped up in an object, also crashes the memory after some time!
I encountered an out of memory with Javascript on the iPad when we were trying to refresh an image very often, like every couple of seconds. It was a bug to refresh that often, but Safari crashed out to the home screen. Once I got the refresh timing under control, the web app functioned fine. It seemed as if the Javascript engine couldn't keep up with garbage collection quickly enough to discard all the old images.
There are issues with memory and the way to solve this problem is very simple. 1) Put all your thumbnails in canvas. You will be creating a lot of new Image objects and drawing them into canvas, but if your thumbnail are very small you should be fine. For the container where you will be displaying the real size image, create only one Image object and reuse this object and make sure to also draw it into a canvas. So, every time a user clicks the thumbnail, you will update your main Image object. Do not insert IMG tags in the page. Insert CANVAS tags instead with the correct width and height of the thumbnails and the main display container. iPad will cry foul if you insert too many IMG tags. So, avoid them!!! Insert only canvas. You can then find the canvas object from the page and get the context. So every time the user clicks a thumbnail, you will get the src of the main image (real size image) and draw it to the main canvas, reusing the main Image object and the firing the events. Clearing the events every time at the beginning.
mainDisplayImage.onload = null;
mainDisplayImage.onerror = null;
...
mainDisplayImage.onload = function() { ... Draw it to main canvas }
mainDisplayImage.onerror = function() { ... Draw the error.gif to main canvas }
mainDisplayImage.src = imgsrc_string_url;
I have create 200 thumbnails and each is like 15kb. The real images are like 1 MB each.
I also had similar problems while rendering large lists of images on iPhones.
In my case displaying even 50 images in the list was enough to either crash the browser or occasionally the entire operating system. For some reason any images rendered onto the page weren't garbage collected, even when pooling and recycling just a few onscreen DOM elements or using the images as background-image property. Even displaying the images directly as Data-URIs is enough to count towards the limit.
The solution ended up being rather simple - using position: absolute on the list items allows them to be garbage collected fast enough to not run into a memory limit. This still involved on having only about 20-30 images in the DOM at any moment, creating and removing the item's DOM nodes by scroll positon finally did the trick.
It seems it's particularily dependent on having webkit-transform':'scale3d() applied to any ancestor of the images in the DOM. Relatively flowing a very tall DOM and rendering it on the GPU pisses off a memory leak in webkit renderer, I guess?
I'm running in a similar issue in Chrome too, developing an extension that loads images in the same page (the popup, actually) replacing old images with new ones.
The memory used by the old images (removed from the DOM) is never freed, consuming all the PC memory in a short time.
Have tried various tricks with CSS, without success.
Using hardware with less memory than a PC, like the iPad, this problem arises earlier, naturally.
I filed a bug with jQuery as jQuery trys to handle memory leaks...so I'd consider this a bug. Hopefully the team can come up with some concise and clever way of handling this problem in Mobile Safari soon.
http://dev.jquery.com/ticket/6944#preview

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