I try to get my head around the relatively new img attribute "loading".
I understand that if an img has the attribute loading="lazy" then it will tell the browsers that support the attribute, that it can be loaded when getting near the viewport.
So why not always set loading="lazy"? Those images that appear instantly on the screen would get rendered anyways, as they already are inside the viewport. So basically loading="lazy" is ignored in that case anyways.
I also see in this demo https://mathiasbynens.be/demo/img-loading-lazy that the pictures in the top of the dom are having the loading="lazy" attribute set.
I got the link above from: https://web.dev/native-lazy-loading/
Thanks in advance :)
You should avoid setting loading=lazy for any images that are in the first visible viewport.
Source: https://web.dev/browser-level-image-lazy-loading/#avoid-lazy-loading-images-that-are-in-the-first-visible-viewport
In short, if the image is not loaded lazily, the browser can start fetching the resource immediately. Lazy images need to wait until the Layout phase of the browser rendering pipeline, to determine if an image is in the viewport or not.
Adding loading=lazy unnecessarily will likely add a small amount of delay until your webpage is fully rendered.
One of the reasons I can think of to not always use lazy loading is when the network can be disrupted. In that case, you want to download as much as possible while the connection is active, so that the most of the page is usable when the connection is down.
It’s a hint to the browser that the image might not be immediately useful/visible and that it should prioritize other resources. The third image in an image carousel or images appearing far down on the page are some good examples of when this attribute is useful.
Overly lazy implementations, such as Firefox, don’t images until they’re scrolled into view. This causes the browser to display a white area while the image is being loaded. This isn’t an ideal user-experience. Chrome, on the other hand, loads images 3000–8000px before they appear on screen which is too eager again.
Chrome won’t load lazy-loaded images even when they’re within the viewport for background-opened tabs. This is caused by a limitation of Chromium’s IntersectionObserver and may be fixed in a future version.
Related
This is quite simple, I want to increase the performance of my page by using canvas to generate diagonal lines pattern instead background-image.
Should I do that? why?
If you're displaying static content, is slower and much more obtuse. and do completely different things, the former being for dynamic graphics using JavaScript and the latter being for static images retrieved from a URI.
Browsers tend to be optimised for loading IMG sources while the HTML is streaming: so you'll see an image before the page has loaded completely. Canvas, on the other hand, will be dependent on the DOM being loaded, so (typically) won't load until the DOMContentLoaded event has fired. Add to that the latency in creating a Canvas context and the memory requirements and it almost certainly isn't what you want if the images are truly static.
If you want to do something fancy with the image why not load the image in an IMG tag and then convert it to a canvas once loaded to do the transformations?
I am trying to make it so these images will line up the way so that the blank.gif will appear in front of the image. i cannot use it as a background image, and i have tried using a negative z-index like -1 but then the image disappears all together on the site i have tried to use it on. my goal is to make the gray and black image appears behind the blank.gif.
things that i have to avoid or will not work are these:
z-index:-1 (just the negative numbers)
use of background image inside of a <div>
and both the images must remain inside a parent element, and my issue is that i cant use any script that needs to be inside of the head of the html. i have tried but cant find a solution. if you have any method of keeping an image from being right clicked and saved so easily then that would be great. any help is appreciated thank you.
image html are here: index.html
code sample:
<html><div style="position:absolute;width:150px;height:150px;display:inline;">
<img src="http://dl.dropbox.com/u/14413762/blank.gif" style="position:static:width:150px;height:150px;left:0px;top:0px;z-index:2;"><img src="http://dl.dropbox.com/u/14413762/bbc/image.png" style="position:absolute;left:0px;top:0px;;z-index:1;">
</div></html>
Yeah.. You're pretty much wasting time that is better spent elsewhere. A person who wants the image is going to get it, either with the web developer tools in firefox or chrome, viewing the page source, etc.
On a real note though, z-index only works with absolute, relative, or fixed positioned elements. It will not work with your statically positioned element that you set to a z-index of 2. I have done what you are trying to acheive with relatively positioned elements, z-index, and either top and left or negative top and left margins.
I'm new to webkit animations and I have been trying out to do this kind of animation
http://demo.jeffrey-way.com/tutsMobile/#site.php?siteName=psdtuts
If you click the list element you will see page sliding in and sliding out.
I want to implement this animation to my app which is built with backbone.js, underscore.js, zepto.js
I could use jqTouch or jquery mobile but I would like to make it as light weight as possible, because I'm building it only for IOS. So thats way I wan't to implement it by my self.
Any hints to make this implementation or should I go with jqTouch?
In this example, there is some sort of (I hate to be vague...) ajax based content loading system. Take a look at the source:
<div data-role="page" id="article.php?siteName=psdtuts&origLink=http%3A%2F%2Fpsd.tutsplus.com%2F%3Fp%3D15026" class="ui-page ui-body-c">
When you first visit, that div doesn't exist. It's created by javascript when content is required, then filled with that content, then translated (animated) into the viewport.
Here is a step by step, deduced from a quick look at the page:
Base page is loaded, including css, javascript, nav list
Script is waiting for a nav item to be clicked.
Upon clicking, an ajax request is made to the content corresponding to the clicked item; determined by href="article.php?siteName=psdtuts&origLink=http://psd.tutsplus.com/?p=15081". My guess? This ajax request is getting content from the same place as psdtuts.com, likely in a database.
While that stuff is loading, javascript shows a loading animation. When loading is complete, it's hidden again.
Once the new content-filled div is created, it is given a default position with its left edge placed right outside of the right edge of the screen. Upon the event of being positioned, javascript then determines the view's dimensions and translates the div across the horizontal dimension. At the same time, the nav list is moved the same direction and distance.
When back is clicked, the view's dimensions are determined again (In case the window size changed) and the nav and content are translated to the right, hiding the content and showing the navigation again.
Repeat
I could be off from how this exact sample is being done, but... Well, this would work.
You wouldn't be that crazy to use a framework for something like this, but I can understand wanting to do a custom job. It would certainly be faster for users, but slower for you. Depending on your intent, that would be just fine.
edit: If you're only serving this to users with webkit, using a framework is even less necessary... If you're not worrying about cross browser support, there's really not a lot going on here that you couldn't accomplish easily with raw javascript.
The only reason I use jQuery for example, most of the time, is to ensure things work alright in most use cases. It just smooths so many things out... Even if 95% of the framework isn't being utilized, it's worth it when you've got a deadline.
I founded out one good example
http://andrew.hedges.name/blog/2009/05/29/animating-your-iphone-web-application
It's not possible to set transparent background for WebBrowser of WP7. To make impression of transparent background I want to do the following workaround. I want:
To find a position and size of WebBrowser on the page.
To get page's background image.
Crop it with values what I found on step 1.
To save result in IsolatedStorage
To parse HTML and place <body background="RESULTBACKGROUND">
MyWebBrowser.NavigateToString(NewHtmlString);
I think this should be a workaround of transparent background and should work.
For now I am trying just to place any .jpg image (let's say test.jpg) on step 5.
But fail. I have "Build Action" property of file set to "Content". It is placed in the root of the project. And <body background="test.jpg"> not working. Back of the WebBrowser is still white.
What I am doing wrong?
UPD:
Step 5 is solved.
2Claus: No! Not only from web. I saved both html file and image file to IsolatedStorage and WebBrowser can show image as a backgroud.
Now the problem is that background cannot be fixed. I tried many differrent things with styles. I also tried to add a fixed div behind my text. Nothing works. The picture is always scrolling with a text. I tried to add onscroll event and pass it scrolled value to move the div in an opposite direction, but div is glued to the page :(
Any ideas?
So assuming you're talking about the WebBrowser control, you're forgetting that the HTML only can refer to urls on the world wide web.
So either you need to host your background images on a website, or you need to inject a CSS style that sets the background to either white or black (the two default background-colours of the platform).
For WebBrowser, You don't actually have to save it to the ISO to make changes on the page. You can load it navigate to it normally, and then use InvokeScript to make the changes via custom JS code. It can be a little tricky though, as you will probably need to heavily rely on the eval and stringization. The problem mentioned by Claus is still there - but you need to do some experiments. With the Mango release and SDK 7.1+, the platform support IsoltatedStorage imagesources in the form of is://path/file - maybe - maybe - maybe squared - the webbrowser's renderer udnerstands them too - then setting your bkg's url to such would work. I doubt though, as it could be seen as some minor security breach, etc
I now bumped into the same background fixed image problem. For someone wandering here I solved it placing content into a fixed-height container (div) therefore the container contents is being scrolled and not the html page, leaving background picture "fixed".
body
{
background-image:url('...');
background-position:-20px -150px;
background-repeat:no-repeat;
background-attachment:fixed;
}
div
{
height:300px;
overflow:scroll;
}
Of course background-position and div height is set specifically for a WebBrowser position in page and it's size.
I have a dojo animation object of about 15 images. I'm also using dojo.fx.chain to link them all together.
Right before I create all my dojo.fadeIn's and dojo.fadeOut's I added in some basic javascript to preload each image.
My question is: Am I doing this the hard way or is there some function/attr I can set in the animation object to do this?
I do not think there is a predefined method in dojo to preload these images for your animation.
I guess you are listening image.onload and image.onerror events to preload images, it is a common method. If you feel it is too difficult and hard to control, you can try a simple clean css way that is to put an invisible div into your page and set background images with these animation images. When the page load, the images are automatically loaded.
dojo Animations are not specifically geared around images, they work on an abstract level and may operate on DOM nodes. So, there's no built-in support for IMG nodes specifically.
There is dojox.image.preload (http://api.dojotoolkit.org/jsdoc/HEAD/dojox.image.preload) which will do the work virsir suggested of loading images into an offscreen div, but it does not (currently) arrange an onLoad event hook for you to detect when they're loaded and thus play your animation.
I imagine you could use preload()'s return value and use it to hook into onLoad, but that's an exercise for the reader. Have a look at the source code, dojox/image/_base.js.