Problem:
Need to execute an action when an element enters the middle third area of the viewport:
Constraints:
I am using Alpine JS.
According to the Alpine intersect docs, I can control the rootMargin property of the underlying IntersectionObserver using .margin, in order to change the limit where the observer will trigger. I'm doing it as follows:
h1 {
margin-top: 95vh;
position: relative;
background-color: blue;
color: white;
z-index: 2;
}
body {
height: 200vh;
}
body::before,
body::after {
content: '';
position: fixed;
left: 0;
right: 0;
height: 33%;
background-color: grey;
z-index: 1;
}
body::before{
top: 0;
}
body::after{
bottom: 0;
}
<html>
<head>
<!-- Alpine Plugins -->
<script defer src="https://unpkg.com/#alpinejs/intersect#3.x.x/dist/cdn.min.js"></script>
<!-- Alpine Core -->
<script defer src="https://unpkg.com/alpinejs#3.x.x/dist/cdn.min.js"></script>
</head>
<body>
<h1 x-data="{ message: 'Alpine Is Working' }"
x-intersect:enter.margin.-33%.0.-33%.0="message = 'ENTERED'"
x-intersect:leave.margin.-33%.0.-33%.0="message = 'LEFT'"
x-text="message"></h1>
</body>
</html>
In the above example, you can see it's not respecting the 33% top/bottom margin with the viewport. I marked those in grey using pseudoelements.
What should happen:
In the example above, it should say "Entered" or "Left" when the element scrolls into and out of the white area.
Any idea on what I may be doing wrong?
Thanks!
Your code wouldn't work for me in the code snippet, but did as soon as I copied it out to a local html file and ran it there.
The iframe is messing with the intersection observer's root.
Your code is useful to me, I hadn't been able to find an example combining the :enter and :leave modifiers.
Related
First-time posting a question, and I avow up front that my HTML/CSS/Javascript knowledge is ... shall we say scrappy. I usually manage, but I can't seem to figure this out.
All I want to do is display an image centered. Then create a canvas, position the canvas over the image, and draw on it. Then have the canvas stay with the image as the browser is re-sized. Here's what I have so far (I confess, I got much of the Javascript code from another poster, and I'm trying to use it as a learning example):
<!DOCTYPE html>
<html>
<head>
<script>
function myInit()
{
hdc = set_canvas();
hdc.fillRect(0, 0, 50, 50);
}
function set_canvas()
{
var img = document.getElementById('audubon_image');
var x = img.offsetLeft,
y = img.offsetTop,
w = img.clientWidth,
h = img.clientHeight;
var c = document.getElementById('myCanvas');
img.parentNode.appendChild(c);
c.style.zIndex = 1;
c.style.left = x + 'px';
c.style.top = y + 'px';
c.setAttribute('width', w+'px');
c.setAttribute('height', h+'px');
hdc = c.getContext('2d');
return(hdc);
}
</script>
<style>
#container
{
text-align: center;
}
canvas
{
pointer-events: none;
position: absolute;
border: 1px solid black;
}
</style>
</head>
<body onload='myInit()'>
<div id="container">
<img src="http://www.sturtz.org/john/audubon/wp-content/uploads/2015/04/Audubon.jpg" id="audubon_image" />
<canvas id='myCanvas'></canvas> <!-- gets re-positioned in myInit(); -->
</div>
</body>
</html>
What's supposed to happen: The image gets placed. Then the Javascript code determines the position and size of the image, and sets the canvas to match. Then draws on the canvas (for the moment, a lovely elegant block box in the upper left corner).
So far, so good. But since the image centered, if the browser is re-sized (specifically made wider or narrower), the image's position moves relative to the left and right edges of the browser window.
With 'position: absolute' specified for the canvas, the canvas does not move (unsurprisingly; I suppose that's what absolute means). So the image and canvas do not stay aligned.
If I change the canvas CSS to 'position: relative', then when I re-size the window, the image and canvas remain in the same position relative to one another (which is what I want). But then I can't get the canvas over the top of the image.
My gut feel is that this should be possible (easy, even), and my lack of knowledge is causing me not to see it.
I think I'm on to it.
Put the canvas in a div. Wrap that and the img in a container div. Specify 'position: relative' for the outer div, 'position: absolute' for the inner div. That way, the x and y coordinates of the div containing the canvas may simply be specified as (0,0).
<!DOCTYPE html>
<html>
<head>
<script>
function myInit()
{
hdc = set_canvas();
hdc.fillRect(0, 0, 50, 50);
}
function set_canvas()
{
var c = document.getElementById('map_canvas');
c.style.zIndex = 1;
c.setAttribute('width', '650px');
c.setAttribute('height', '300px');
hdc = c.getContext('2d');
return(hdc);
}
</script>
<style>
#image_container
{
margin-left: auto;
margin-right: auto;
width: 650px;
position: relative;
}
#canvas_container
{
position: absolute;
top: 0px;
left: 0px;
}
#map_canvas
{
}
</style>
</head>
<body onload='myInit()'>
<div id="image_container">
<img src="http://www.sturtz.org/john/audubon/wp-content/uploads/2015/04/Audubon.jpg" id="audubon_image" />
<div id="canvas_container">
<canvas id="map_canvas"></canvas>
</div>
</div>
</body>
</html>
How to position the canvas directly over the img with the container horizontally centered.
Keep the canvas directly over the image
Set both #audubon_image and #myCanvas to position:absolute inside the #container that's set to position:relative.
Center the container div
margin:0 auto; to center #container on the page.
CSS
#container{
margin:0 auto;
position:relative;
border:1px solid blue;
}
#audubon_image,#myCanvas{position:absolute; top:0px; left:0px;}
#audubon_image{border:1px solid green;}
#myCanvas{ border:1px solid red;}
Javascript
Set the #container's CSS size and #canvas's element size to equal the img's size. Be sure to set the canvas element size (not css size) or your canvas drawings will be distorted.
// get a reference to #audubon_image
var img=document.getElementById('audubon_image');
// set #container's size to equal the #audubon_image size
var container=document.getElementById('container');
container.style.width=img.width+'px';
container.style.height=img.height+'px';
// set #myCanvas's size to equal the #audubon_image size
var canvas=document.getElementById('myCanvas');
canvas.width=img.width;
canvas.height=img.height;
Note: Once in a great while, browsers will fire window.onload before the image's width & height are set (shame on you browsers!). So in production, you might "defensively" wrap the javascript inside a setTimeout of 1 second to be sure the image's width & height have been set.
Full code and a Demo:
window.onload = (function() {
// get a reference to #audubon_image
var img = document.getElementById('audubon_image');
// set #container's size to equal the #audubon_image size
var container = document.getElementById('container');
container.style.width = img.width + 'px';
container.style.height = img.height + 'px';
// set #myCanvas's size to equal the #audubon_image size
var canvas = document.getElementById('myCanvas');
canvas.width = img.width;
canvas.height = img.height;
});
body {
background-color: ivory;
}
#container {
margin: 0 auto;
position: relative;
border: 1px solid blue;
}
#audubon_image,
#myCanvas {
position: absolute;
top: 0px;
left: 0px;
}
#audubon_image {
border: 1px solid green;
}
#myCanvas {
border: 1px solid red;
}
<div id="container">
<img id="audubon_image" src='https://dl.dropboxusercontent.com/u/139992952/multple/character3.png' />
<canvas id='myCanvas'></canvas>
</div>
I'm experimenting with Wordpress and (the recent version of) dompdf at the moment and ran into an annoying problem regarding the formating.
My Problem: The top-margin of the main content seems not to be considered on the second page generated, resulting in an overlapping with my logo. You can view the generated PDF under this link.
The relevant code from which the PDF is generated reads as follows (it is not perfect yet as i want to resolve the issue first):
function ppt_pdf_output() {
// post-ID of referring page needed
$post=get_post($_POST['postid']);
$output = '<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<title>'.$post->post_title.'</title>
<style>
body {
margin: 30px 0 0 0;
font-family:sans-serif;
text-align:left;
}
img {
margin: 15px 0;
}
#header,
#footer {
position: fixed;
left: 0;
right: 0;
color: #aaa;
font-size: 0.9em;
line-height:1.2em;
}
#header {
top: -30px;
/*border-bottom: 0.1pt solid #aaa;*/
}
#footer {
bottom: 0;
border-top: 0.1pt solid #aaa;
}
#header table,
#footer table {
width: 100%;
border-collapse: collapse;
border: none;
text-align: center;
color: #000;
font-size: 24px;
}
.entry-content {
margin: 100px auto 35px auto;
top: 0; left: 0; bottom: 0; right: 0;
background-color: #d1d977;
width:90%; height:auto;
}
.entry-title {
font-size: 18px;
text-align: center;
}
#header td,
#footer td {
padding: 0;
width: 50%;
}
#footer .page-number {
text-align: center;
}
.page-number:before {
content: "Seite " counter(page);
}
.gallery-item {
display:inline-block;
}
br[style] {
display:none;
}
.gallery + p {
clear:left;
}
</style>
</head>
<body><div id="header">
<table>
<tr>
<td>ANTRAG</td>
<td style="text-align: right;"><img src="path/to/logo.png" /></td>
</tr>
</table>
</div>
<div id="footer">
<div class="page-number"></div>
</div>';
$output .='
<!--<h1 class="entry-title">'. $post->post_title .'</h1>-->
<div class="entry-content">' .
apply_filters('the_content',$post->post_content) . '</div>';
$output .= '</body></html>';
return $output;
}
As you can see, the formatting on the first page is as it should be (or at least as I intended it to be), but after the page break the content area (for visualization reasons provided with a green background) just starts at the beginning of the page, regardless of which number I give the margin.
Has anybody an idea how to resolve this issue? I've been working on this for countless hours and just don't know what to do at this point.
Any help would be greatly appreciated.
Kind regards
Olli
UPDATE: Of course I found this solution only just. I will try this and see if I can get the issue resolved with this.
UPDATE2: Still no luck. I'm now stuck with the following code (the output can be found under the link provided earlier):
function ppt_pdf_output() {
// post-ID of referring page needed
$post=get_post($_POST['postid']);
$output = '<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<title>'.$post->post_title.'</title>
<style>
#page {
margin: 120px 50px 80px 50px;}
#header {
position: fixed;
top: -82px;
width: 100%;
height: 109px;
background: #aaa url("path/to/logo.png") no-repeat right;
}
#content {
width: 100%;
height: 85%;
background-color: #d1d977;
}
footer {
position: fixed;
bottom: -65px;
height: 30px;
background-color: #333399;
}
footer .page-number {
text-align: center;
}
.page-number:before {
content: "Seite " counter(page);
}
br[style] {
display:none;
}
</style>
</head>
<body><div id="header">
<h2>ANTRAG</h2>
</div>
<footer>
<div class="page-number"></div>
</footer>';
$output .='<h1>'. $post->post_title .'</h1>
<div id="content">' .
apply_filters('the_content',$post->post_content) . '</div>';
$output .= '</body></html>';
return $output;
}
It seems just so fragile. For example, as soon as I change the font-size of the h1 element, it gets overlapped by the logo. After the page break, it looks okay, but that just seems an coincidence - as soon as I change the font-size or the text, the text again gets overlapped. Will absolute positioning change anything or do you have any other tipps as how to resolve this anoying issue? Margins of any kind don't seem to work either.
You're on the right track. As you've seen, when an element is split across pages (as your content area is) some of the formatting information does not follow. This is by design.
The correct tact is to define the page margins so that they are large enough to hold your header/footer content and place the header/footer into that space. The content will then just fill the "body" of the document (i.e. the space inside the page margins). This is what you've attempted, but you haven't given enough space for the header. The header is positioned 82px inside the page margin but the height of the header is 109px. Because of this any content that has a small margin will still fall under the header.
Try this instead:
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<title>"Kaffeefahrten" in Bornheim: hart durchgreifen, Senioren vor Betrügern schützen</title>
<style>
#page {
margin: 120px 50px 80px 50px;
}
#header {
position: fixed;
top: -115px;
width: 100%;
height: 109px;
background: #aaa url("path/to/logo.png") no-repeat right;
}
#content {
background-color: #d1d977;
}
footer {
position: fixed;
bottom: -65px;
height: 30px;
background-color: #333399;
}
footer .page-number {
text-align: center;
}
.page-number:before {
content: "Seite " counter(page);
}
br[style] {
display:none;
}
</style>
</head>
<body>
<div id="header">
<h2>ANTRAG</h2>
</div>
<footer>
<div class="page-number"></div>
</footer>
<h1>"Kaffeefahrten" in Bornheim: hart durchgreifen, Senioren vor Betrügern schützen</h1>
<div id="content">
...
</div>
</body>
</html>
Note that you also don't have to specify any height/width for the content element (unless you want to further constrict the space it uses).
With CSS3 you could go with your original styling and re-use the margins by applying the box-decoration-break property. However as of writing dompdf does not yet support this property.
My webpage contains several divs. Some are set to width: 100%, so they fill the whole page width.
But at the top of the page there is a small whitespace before the first element shows up. Moreover, that same whitespace is visible left and right from elements spanning the whole page width.
I cannot figure out why. If I set:
html, body {
width: 100%;
}
then the whitespace remains but the page is just stretched out to fit the image width of a div.
Can anyone help? It's probably pretty simple but I must be overlooking something.
Thank you.
EDIT: I must mention I'm using a parallax element. This uses a padding, so the image does fills the whole div and does not leave a black area on top. The HTML is:
<div class="js-background-1 container">
</div>
The CSS:
.container {
padding-top: 200px;
}
.js-background-1 {
background: transparent url(url/to/image) center 0 no-repeat;
}
And the javascript:
<script type="text/javascript">
var $window = $(window);
var velocity = 0.4;
function update(){
var pos = $window.scrollTop();
$('.container').each(function() {
var $element = $(this);
var height = $element.height();
$(this).css('backgroundPosition', '50% ' + Math.round((height - pos) * velocity) + 'px');
});
};
$window.bind('scroll', update);
</script>
I used the tutorial from http://www.webdesign.org/how-to-create-a-parallax-scrolling-website.22336.html, so there is where it is from. I changed the HTML a bit for my website, but the rest is the same.
I saw the comment about the margin and padding set to 0, but that leads to my div to have a blank space if you don't scroll far enough.
You must remove the margin on body:
body {
padding:0;
margin:0;
}
You can also remove padding and margin on html and body
html, body {
padding:0;
margin:0;
}
See it on jsfiddle
But I would not advise to use * (the universal selector)
* {
margin: 0px;
padding: 0px;
}
This would remove padding and margins on all elements.
The good method is to always use at the begining of the file (I forgot to metion this):
*{
margin: 0px;
padding: 0px;
}
This two line's at the begining of main CSS file fix many problem's that you can encounter.
Hope it'll help you.
padding-bottom: 20px;
border: 1px solid red !important;
margin: 0;
padding: 0;
width: 100%;
I have three div elements: one as a header, one as a footer, and a center content div. the div in the center needs to expand automatically with content, but I would like a min-height such that the bottom div always at least reaches the bottom of the window, but is not fixed there on longer pages.
For example:
<div id="a" style="height: 200px;">
<p>This div should always remain at the top of the page content and should scroll with it.</p>
</div>
<div id="b">
<p>This is the div in question. On longer pages, this div needs to behave normally (i.e. expand to fit the content and scroll with the entire page). On shorter pages, this div needs to expand beyond its content to a height such that div c will reach the bottom of the viewport, regardless of monitor resolution or window size.
</div>
<div id="c" style="height: 100px;">
<p>This div needs to remain at the bottom of the page's content, and scroll with it on longer pages, but on shorter pages, needs to reach the bottom of the browser window, regardless of monitor resolution or window size.</p>
</div>
Just look for my solution on jsfiddle, it is based on csslayout
html,
body {
margin: 0;
padding: 0;
height: 100%; /* needed for container min-height */
}
div#container {
position: relative; /* needed for footer positioning*/
height: auto !important; /* real browsers */
min-height: 100%; /* real browsers */
}
div#header {
padding: 1em;
background: #efe;
}
div#content {
/* padding:1em 1em 5em; *//* bottom padding for footer */
}
div#footer {
position: absolute;
width: 100%;
bottom: 0; /* stick to bottom */
background: #ddd;
}
<div id="container">
<div id="header">header</div>
<div id="content">
content<br/>content<br/>content<br/>content<br/>content<br/>content<br/>content<br/>content<br/>content<br/>content<br/>content<br/>content<br/>content<br/>content<br/>content<br/>content<br/>content<br/>content<br/>
</div>
<div id="footer">
footer
</div>
</div>
I found this courtesy of ryanfait.com. It's actually remarkably simple.
In order to float a footer to the bottom of the page when content is shorter than window-height, or at the bottom of the content when it is longer than window-height, utilize the following code:
Basic HTML structure:
<div id="content">
Place your content here.
<div id="push"></div>
</div>
<div id="footer">
Place your footer information here.
</footer>
Note: Nothing should be placed outside the '#content' and '#footer' divs unless it is absolutely positioned.
Note: Nothing should be placed inside the '#push' div as it will be hidden.
And the CSS:
* {
margin: 0;
}
html, body {
height: 100%;
}
#content {
min-height: 100%;
height: auto !important; /*min-height hack*/
height: 100%; /*min-height hack*/
margin-bottom: -4em; /*Negates #push on longer pages*/
}
#footer, #push {
height: 4em;
}
To make headers or footers span the width of a page, you must absolutely position the header.
Note: If you add a page-width header, I found it necessary to add an extra wrapper div to #content. The outer div controls horizontal spacing while the inner div controls vertical spacing. I was required to do this because I found that 'min-height:' works only on the body of an element and adds padding to the height.
*Edit: missing semicolon
If #top and #bottom have fixed heights, you can use:
#top {
position: absolute;
top: 0;
height: 200px;
}
#bottom {
position: absolute;
bottom: 0;
height: 100px;
}
#central {
margin-top: 200px;
margin-bot: 100px;
}
update
If you want #central to stretch down, you could:
Fake it with a background on parent;
Use CSS3's (not widely supported, most likely) calc();
Or maybe use javascript to dynamically add min-height.
With calc():
#central {
min-height: calc(100% - 300px);
}
With jQuery it could be something like:
$(document).ready(function() {
var desiredHeight = $("body").height() - $("top").height() - $("bot").height();
$("#central").css("min-height", desiredHeight );
});
to get dynamic height based on browser window. Use vh instead of %
e.g: pass following height: 100vh; to the specific div
As mentioned elsewhere, the CSS function calc() can work nicely here. It is now mostly supported. You could use like:
.container
{
min-height: 70%;
min-height: -webkit-calc(100% - 300px);
min-height: -moz-calc(100% - 300px);
min-height: calc(100% - 300px);
}
No hack or js needed. Just apply the following rule to your root element:
min-height: 100%;
height: auto;
It will automatically choose the bigger one from the two as its height, which means if the content is longer than the browser, it will be the height of the content, otherwise, the height of the browser. This is standard css.
You propably have to write some JavaScript, because there is no way to estimate the height of all the users of the page.
It's hard to do this.
There is a min-height: css style, but it doesn't work in all browsers. You can use it, but the biggest problem is that you will need to set it to something like 90% or numbers like that (percents), but the top and bottom divs use fixed pixel sizes, and you won't be able to reconcile them.
var minHeight = $(window).height() -
$('#a').outerHeight(true) -
$('#c').outerHeight(true));
if($('#b').height() < minHeight) $('#b').height(minHeight);
I know a and c have fixed heights, but I rather measure them in case they change later.
Also, I am measuring the height of b (I don't want to make is smaller after all), but if there is an image in there that did not load the height can change, so watch out for things like that.
It may be safer to do:
$('#b').prepend('<div style="float: left; width: 1px; height: ' + minHeight + 'px;"> </div>');
Which simply adds an element into that div with the correct height - that effectively acts as min-height even for browsers that don't have it. (You may want to add the element into your markup, and then just control the height of it via javascript instead of also adding it that way, that way you can take it into account when designing the layout.)
My page has a resolution of 800x480. It has been designed as such. Now in Firefox (I have control over the viewers machine), I want to zoom the whole screen to 800x600. I know that there is a zoom option, but that does it proportionally (e.g. 150%). Is it possible to somehow to only stretch the 480 to 600 (a sort of a zoom).
I have a valid reason to do this and am aware of the aspect ratio issues that could arise.
Thank you for your time.
You can do this in Firefox 3.5 (Gecko 1.9.1) using CSS3 2d transforms.
Here's an example with two DIVs where the second is stretched from 800x480 to 800x600.
<!DOCTYPE html>
<html>
<head>
<style type="text/css">
html, body
{
background-color: #000;
color: #fff;
}
.viewport
{
width: 800px;
height: 480px;
background-color: gold;
color: #000;
position: absolute;
left: 0px;
top: 0px;
}
.stretched
{
background-color: rgba(255, 0, 0, 0.5);
-moz-transform: scaleY(1.25);
-moz-transform-origin: 0 0;
}
</style>
</head>
<body>
<div class="viewport"><button>Normal</button></div>
<div class="viewport stretched"><br><br><button>Stretched</button></div>
</body>
</html>
See also:
Using CSS transforms
You can use:
self.resizeTo(width, height);
Although I think Firefox has a default setting in the preferences which prevents this from working.