I'm currently writing an HTML5 P&C aventure.
Since there are many images and sprites to load before the game can start I wanted to preload all images.
My idea was to create a single <img> and make it visibility: hidden;, so the user does not see anything.
After every loaded image I want to execute a function that updates a progressbar.
So I did something like this:
loadImages: function () {
$('#preLoader').attr('src', this.__images[0]).on('load', this.loadCallback);
},
loadCallback: function () {
this.__images.splice(0, 1);
Game.events.trigger('progressbar:bar:step');
if(this.__images.length > 0) {
this.loadImages();
}
else if(!this.__fired) {
this.__fired = true;
this.trigger('finished');
}
}.$bound(),
this.__images is an array containing all urls to be loaded, the callback function basically calls the progressbar to update and checks if there are images left and then again calls the first function.
Thing is, that it seems, that the load event does not really wait until the image is loaded, because under a 1ms after the src attribut of the <img> has been changed the callback gets fired.
So this might not work properly
Is there a way to achieve this like I want to?
Basically I want the image to be loaded complete and then fire the callback, then again load the image, etc... until all images in the array are loaded.
I ended up using this jquery plugin: http://alz.so/imageloader/
It has all the functionality I need and even more.
I'm currently working on a web application which has a page which displays a single chart (a .png image). On another part of this page there are a set of links which, when clicked, the entire page reloads and looks exactly the same as before except for the chart in the middle of the page.
What I want to do is when a link is clicked on a page just the chart on the page is changed. This will speed things up tremendously as the page is roughly 100kb large, and don't really want to reload the entire page just to display this.
I've been doing this via JavaScript, which works so far, using the following code
document.getElementById('chart').src = '/charts/10.png';
The problem is that when the user clicks on the link, it may take a couple of seconds before the chart changes. This makes the user think that their click hasn't done anything, or that the system is slow to respond.
What I want to happen is display a spinner / throbber / status indicator, in place of where the image is while it is loading, so when the user clicks the link they know at least the system has taken their input and is doing something about it.
I've tried a few suggestions, even using a psudo time out to show a spinner, and then flick back to the image.
A good suggestion I've had is to use the following
<img src="/charts/10.png" lowsrc="/spinner.gif"/>
Which would be ideal, except the spinner is significantly smaller than the chart which is being displayed.
Any other ideas?
I've used something like this to preload an image and then automatically call back to my javascript when the image is finished loading. You want to check complete before you setup the callback because the image may already be cached and it may not call your callback.
function PreloadImage(imgSrc, callback){
var objImagePreloader = new Image();
objImagePreloader.src = imgSrc;
if(objImagePreloader.complete){
callback();
objImagePreloader.onload=function(){};
}
else{
objImagePreloader.onload = function() {
callback();
// clear onLoad, IE behaves irratically with animated gifs otherwise
objImagePreloader.onload=function(){};
}
}
}
You could show a static image that gives the optical illusion of a spinny-wheel, like these.
Using the load() method of jQuery, it is easily possible to do something as soon as an image is loaded:
$('img.example').load(function() {
$('#spinner').fadeOut();
});
See: http://api.jquery.com/load-event/
Use the power of the setTimeout() function (More info) - this allows you set a timer to trigger a function call in the future, and calling it won't block execution of the current / other functions (async.).
Position a div containing the spinner above the chart image, with it's css display attribute set to none:
<div> <img src="spinner.gif" id="spinnerImg" style="display: none;" /></div>
The nbsp stop the div collapsing when the spinner is hidden. Without it, when you toggle display of the spinner, your layout will "twitch"
function chartOnClick() {
//How long to show the spinner for in ms (eg 3 seconds)
var spinnerShowTime = 3000
//Show the spinner
document.getElementById('spinnerImg').style.display = "";
//Change the chart src
document.getElementById('chart').src = '/charts/10.png';
//Set the timeout on the spinner
setTimeout("hideSpinner()", spinnerShowTime);
}
function hideSpinner() {
document.getElementById('spinnerImg').style.display = "none";
}
Use CSS to set the loading animation as a centered background-image for the image's container.
Then when loading the new large image, first set the src to a preloaded transparent 1 pixel gif.
e.g.
document.getElementById('mainimg').src = '/images/1pix.gif';
document.getElementById('mainimg').src = '/images/large_image.jpg';
While the large_image.jpg is loading, the background will show through the 1pix transparent gif.
Building on Ed's answer, I would prefer to see something like:
function PreLoadImage( srcURL, callback, errorCallback ) {
var thePic = new Image();
thePic.onload = function() {
callback();
thePic.onload = function(){};
}
thePic.onerror = function() {
errorCallback();
}
thePic.src = srcURL;
}
Your callback can display the image in its proper place and dispose/hide of a spinner, and the errorCallback prevents your page from "beachballing". All event driven, no timers or polling, plus you don't have to add the additional if statements to check if the image completed loading while you where setting up your events - since they're set up beforehand they'll trigger regardless of how quickly the images loads.
Some time ago I have written a jQuery plugin which handles displaying a spinner automatically http://denysonique.github.com/imgPreload/
Looking in to its source code should help you with detecting when to display the spinner and with displaying it in the centre of the loaded image.
I like #duddle's jquery method but find that load() isn't always called (such as when the image is retrieved from cache in IE). I use this version instead:
$('img.example').one('load', function() {
$('#spinner').remove();
}).each(function() {
if(this.complete) {
$(this).trigger('load');
}
});
This calls load at most one time and immediately if it's already completed loading.
put the spinner in a div the same size as the chart, you know the height and width so you can use relative positioning to center it correctly.
Aside from the lowsrc option, I've also used a background-image on the img's container.
Be aware that the callback function is also called if the image src doesn't exist (http 404 error). To avoid this you can check the width of the image, like:
if(this.width == 0) return false;
#iAn's solution looks good to me. The only thing I'd change is instead of using setTimeout, I'd try and hook into the images 'Load' event. This way, if the image takes longer than 3 seconds to download, you'll still get the spinner.
On the other hand, if it takes less time to download, you'll get the spinner for less than 3 seconds.
I would add some random digits to avoid the browser cache.
Is it possible to set the loop count of a GIF image using JavaScript and then publish an event when it stops playing?
For example something like:
//html code
<img src="myImage.gif" id="img1"/>
//Javascript code
var image = document.getElementById('img1');
//Image must stop playing after 3 loops
image.setLoopCount = 3;
here is how i would suggest doing it:
extract frames form gif file (you can do it online using for instace -> http://imgops.com/)
use javascript to change pictures, simulating animation (that way you can keep track of how many loops you have done)
Here is a jsFiddle link http://jsfiddle.net/qustosh/n5zWH/9/
I used jQuery. I did three loops and i threw a callback function at the end.
For a design side solution, you can set the GIF image to only loop a certain number of times with Photoshop. Then just use window.setTimeout(callback, milliseconds) to trigger your custom event.
You can calculate the time out from the interval used to display each frame of the animation.
I integrated a slider on my brothers website. He wants some preloading, so the the first image of the slide lasts longer than the rest, so the slider can load all images while the first image shows. Do you have any ideas how to delay just the first slide? I tried to find something inside the Javascript file but I dont think its a good Idea for me to work in the source.
Link: http://www.davidgoltz.de/2011/anna-bederke-actor/
Thank you!
Initially when you start set auto to 0 so it doesn't auto change.
Then after a delay (use setTimeout()) set auto to the new value.
i assume you know the number of images should be loaded. then you can set a counter and trigger auto change event;
var counter = 0;
$(".class-of-images-should-be-loaded").bind("load",function(){
counter++;
if(counter == n){ //n - number of images
//trigger your event
}
}
put a single class to all of the images and use it as the selector.
you can use "settimeout" either but if the connection is very slow, there might be unloaded images in slideshow.
*i used jQuery because you have jQuery library in your web page
I have created a Windows Sidebar Countdown gadget where there is a PIC in the BG and below it there's that countdown when finished it shows a text message , Now what I want to do is that I want to add a slideshow in the BG ( of 3 to 4 images) ... So experts please guide me with this.
You can use the setTimeout method from javascript, and after every few seconds change the background image in the body.
document.body.background = "image.gif"
eg.
setTimeout('changeImage(1)',1000);
function changeImage(i)
{
if i == 4 return;
document.body.background = 'image'+i+'.gif';
setTimeout('changeImage('+(i+1)+')',1000);
}
You should have the images image1.gif, image2.gif and so on in the same folder as your gadget.html