We Keep Coding

Turning HTML content in to a canvas element [duplicate]

It would be incredibly useful to be able to temporarily convert a regular element into a canvas. For example, say I have a styled div that I want to flip. I want to dynamically create a canvas, "render" the HTMLElement into the canvas, hide the original element and animate the canvas.
Can it be done?

There is a library that try to do what you say.
See this examples and get the code
http://hertzen.com/experiments/jsfeedback/
http://html2canvas.hertzen.com/
Reads the DOM, from the html and render it to a canvas, fail on some, but in general works.

Take a look at this tutorial on MDN: https://developer.mozilla.org/en/HTML/Canvas/Drawing_DOM_objects_into_a_canvas (archived)
Its key trick was:
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var data = '<svg xmlns="http://www.w3.org/2000/svg" width="200" height="200">' +
'<foreignObject width="100%" height="100%">' +
'<div xmlns="http://www.w3.org/1999/xhtml" style="font-size:40px">' +
'<em>I</em> like ' +
'<span style="color:white; text-shadow:0 0 2px blue;">' +
'cheese</span>' +
'</div>' +
'</foreignObject>' +
'</svg>';
var DOMURL = window.URL || window.webkitURL || window;
var img = new Image();
var svg = new Blob([data], {type: 'image/svg+xml;charset=utf-8'});
var url = DOMURL.createObjectURL(svg);
img.onload = function () {
ctx.drawImage(img, 0, 0);
DOMURL.revokeObjectURL(url);
}
img.src = url;
That is, it used a temporary SVG image to include the HTML content as a "foreign element", then renders said SVG image into a canvas element. There are significant restrictions on what you can include in an SVG image in this way, however. (See the "Security" section for details — basically it's a lot more limited than an iframe or AJAX due to privacy and cross-domain concerns.)

Sorry, the browser won't render HTML into a canvas.
It would be a potential security risk if you could, as HTML can include content (in particular images and iframes) from third-party sites. If canvas could turn HTML content into an image and then you read the image data, you could potentially extract privileged content from other sites.
To get a canvas from HTML, you'd have to basically write your own HTML renderer from scratch using drawImage and fillText, which is a potentially huge task. There's one such attempt here but it's a bit dodgy and a long way from complete. (It even attempts to parse the HTML/CSS from scratch, which I think is crazy! It'd be easier to start from a real DOM node with styles applied, and read the styling using getComputedStyle and relative positions of parts of it using offsetTop et al.)

You can use dom-to-image library (I'm the maintainer).
Here's how you could approach your problem:
var parent = document.getElementById('my-node-parent');
var node = document.getElementById('my-node');
var canvas = document.createElement('canvas');
canvas.width = node.scrollWidth;
canvas.height = node.scrollHeight;
domtoimage.toPng(node).then(function (pngDataUrl) {
var img = new Image();
img.onload = function () {
var context = canvas.getContext('2d');
context.translate(canvas.width, 0);
context.scale(-1, 1);
context.drawImage(img, 0, 0);
parent.removeChild(node);
parent.appendChild(canvas);
};
img.src = pngDataUrl;
});
And here is jsfiddle

Building on top of the Mozdev post that natevw references I've started a small project to render HTML to canvas in Firefox, Chrome & Safari. So for example you can simply do:
rasterizeHTML.drawHTML('<span class="color: green">This is HTML</span>'
+ '<img src="local_img.png"/>', canvas);
Source code and a more extensive example is here.

No such thing, sorry.
Though the spec states:
A future version of the 2D context API may provide a way to render fragments of documents, rendered using CSS, straight to the canvas.
Which may be as close as you'll get.
A lot of people want a ctx.drawArbitraryHTML/Element kind of deal but there's nothing built in like that.
The only exception is Mozilla's exclusive drawWindow, which draws a snapshot of the contents of a DOM window into the canvas. This feature is only available for code running with Chrome ("local only") privileges. It is not allowed in normal HTML pages. So you can use it for writing FireFox extensions like this one does but that's it.

You could spare yourself the transformations, you could use CSS3 Transitions to flip <div>'s and <ol>'s and any HTML tag you want. Here are some demos with source code explain to see and learn: http://www.webdesignerwall.com/trends/47-amazing-css3-animation-demos/

the next code can be used in 2 modes, mode 1 save the html code to a image, mode 2 save the html code to a canvas.
this code work with the library: https://github.com/tsayen/dom-to-image
*the "id_div" is the id of the element html that you want to transform.
**the "canvas_out" is the id of the div that will contain the canvas
so try this code.
:
function Guardardiv(id_div){
var mode = 2 // default 1 (save to image), mode 2 = save to canvas
console.log("Process start");
var node = document.getElementById(id_div);
// get the div that will contain the canvas
var canvas_out = document.getElementById('canvas_out');
var canvas = document.createElement('canvas');
canvas.width = node.scrollWidth;
canvas.height = node.scrollHeight;
domtoimage.toPng(node).then(function (pngDataUrl) {
var img = new Image();
img.onload = function () {
var context = canvas.getContext('2d');
context.drawImage(img, 0, 0);
};
if (mode == 1){ // save to image
downloadURI(pngDataUrl, "salida.png");
}else if (mode == 2){ // save to canvas
img.src = pngDataUrl;
canvas_out.appendChild(img);
}
console.log("Process finish");
});
}
so, if you want to save to image just add this function:
function downloadURI(uri, name) {
var link = document.createElement("a");
link.download = name;
link.href = uri;
document.body.appendChild(link);
link.click();
}
Example of use:
<html>
<head>
</script src="/dom-to-image.js"></script>
</head>
<body>
<div id="container">
All content that want to transform
</div>
<button onclick="Guardardiv('container');">Convert<button>
<!-- if use mode 2 -->
<div id="canvas_out"></div>
</html>
Comment if that work.
Comenten si les sirvio :)

The easiest solution to animate the DOM elements is using CSS transitions/animations but I think you already know that and you try to use canvas to do stuff CSS doesn't let you to do. What about CSS custom filters? you can transform your elements in any imaginable way if you know how to write shaders. Some other link and don't forget to check the CSS filter lab.
Note: As you can probably imagine browser support is bad.

function convert() {
dom = document.getElementById('divname');
var script,
$this = this,
options = this.options,
runH2c = function(){
try {
var canvas = window.html2canvas([ document.getElementById('divname') ], {
onrendered: function( canvas ) {
window.open(canvas.toDataURL());
}
});
} catch( e ) {
$this.h2cDone = true;
log("Error in html2canvas: " + e.message);
}
};
if ( window.html2canvas === undefined && script === undefined ) {
} else {.
// html2canvas already loaded, just run it then
runH2c();
}
}

Div to image with jQuery/JavaScript

I am trying to convert div to image using html2canvas library. I tried but no success can't convert full div to image, the dropper is missing in image.
URL: https://www.makethatvape.com/ejuicecalc/
Tried with code:
html2canvas($("#widget")).then(function(canvas) {
bimg = canvas.toDataURL(); // by default png
});
So, any idea how to overcome this problem. I played with html2canvas and it work for text and CSS div to canvas conversion.

Try this
<div id="copyDiv"></div>
var element = $("#widget"); // global variable
var getCanvas; // global variable
html2canvas(element, {
onrendered: function (canvas) {
$("#copyDiv").append(canvas);
getCanvas = canvas;
}
});
Note: If HTML markup contains an image tag, then for some browsers the above code will not be able to create the image of it. To make this work you need to use 2 parameters i.e. allowTaint, useCORS
Sample code :
html2canvas(document.getElementById("html-content-holder"), {
allowTaint: true, useCORS: true
}).then(function (canvas) {
var anchorTag = document.createElement("a");
document.body.appendChild(anchorTag);
document.getElementById("previewImg").appendChild(canvas);
anchorTag.download = "filename.jpg";
anchorTag.href = canvas.toDataURL();
anchorTag.target = '_blank';
anchorTag.click();
});
Detail Article: Convert HTML to image using jQuery / Javascript with live demos

Simpler way to do it:
var convertMeToImg = $('#myDiv')[0];
html2canvas(convertMeToImg).then(function(canvas) {
$('#resultsDiv').append(canvas);
});
https://html2canvas.hertzen.com/getting-started

Convert Canvas to image then download

I am trying to convert a section of my site into a downloadable image.
Firstly I convert the html to a canvas using:
$(function() {
$("#download").click(function() {
html2canvas($("#the-grid"), {
onrendered: function(canvas) {
theCanvas = canvas;
document.body.appendChild(canvas);
$("#saved").append(canvas);
$("#saved canvas").attr('id', 'scan');
}
});
Which works fine the canvas get generated and all look's good.
I then want to turn that into an image which I can use for thumbnails later but also initiate a download of the image.
To do so I complete the function like this.
$(function() {
$("#download").click(function() {
html2canvas($("#the-grid"), {
onrendered: function(canvas) {
theCanvas = canvas;
document.body.appendChild(canvas);
$("#saved").append(canvas);
$("#saved canvas").attr('id', 'scan');
var c=document.getElementById("scan");
var d=c.toDataURL("image/png");
var w=window.open('about:blank','Download Mix');
w.document.write("<img src='"+d+"' alt='Custom Blend'/>");
}
});
But it doesn't work.
The error's I get are totally irrelevant.
I am an experienced developer but I'm pretty new to Jquery so any help would be appreciated.
UPDATE
Got it to work.
Create image like this
$(function () {
$("#download").click(function () {
html2canvas($("#the-grid"), {
onrendered: function (canvas) {
theCanvas = canvas;
document.body.appendChild(canvas);
$("#saved").append(canvas);
$("#saved canvas").attr('id', 'scan');
var image = canvas.toDataURL("image/png");
$("#saved").append("<img src='"+image+"' alt='Custom Blend'/>");
}
});
image html ends up looking like
<img src="data:image/png;base64,iVBORw0KGgoAAAANS..." alt="Custom Blend">

Maybe this can help you :
var image = canvas.toDataURL("image/png"); // build url of the image
window.location.href=image; //activate download
image = "<img src='"+image+"'/>"; // set canvas image as source

Here's how I did this (note, there's no way to download a file in Safari and set the filename without pinging a server):
First, you need to get the canvas as a png: var img = canvas.toDataUrl('image/png');
Then, you'll want to convert that dataURL to a blob. For a good way to do that, see this function.
Now you want to download that blob. This will work in all browsers but Safari:
if (window.navigator.msSaveBlob) {
window.navigator.msSaveBlob(blob, 'image.png');
} else {
var url = window.URL || window.webkitURL;
var objectURL = url.createObjectURL(blob);
var ele = $('<a target="_blank"></a>')
.hide()
.attr('download', 'image.png')
.attr('href', objectURL);
$('body').append(ele);
var clickEvent = new MouseEvent('click', {
'view': window,
'bubbles': true,
'cancelable': false,
});
ele[0].dispatchEvent(clickEvent);
window.setTimeout(function() {
url.revokeObjectURL(objectURL);
ele.remove();
}, 1000);
}
This creates an invisible link and simulates a click on it. The click() function won't work in Firefox, so you have to create an event and dispatch it by hand. Finally, it does a bit of clean up by removing the invisible link after one second. In IE, it uses the method provided by Microsoft. This will download the image with the filename "image.png". It also has the benefit of being able to download any blob, if you need to be able to do more with your code. Hopefully this helps!

Getting original image for cropping, ignoring the width attribute?

My user can upload really big images, and for cropping and display purposes i'm adding width attribute so it will fit well in the browser window. Real image size can be - say 1920 x 1080 px.
<!-- width added for display purpose -->
<img class="croppable" src="images/fhd.jpg" width="640" />
In order to calculate real selection box dimension (if the x coordinate is 20px then would be 60px in the original full hd picture) i need to get the full image size before apply the width attribute.
The problem is that this will return 640 as value, taking into account the width attribute:
// Important: Use load event to avoid problems with webkit browser like safari
// when using cached images
$(window).load(function(){
$('img.croppable').each(function(){
alert(this.width);
});
});
Please don't flag this as duplicate since what i'm asking is completly different from simple image width/height retrival (which works, actually).
EDIT: Chris G. solution seems not working:
$(window).load(function(){
$('img.croppable').each(function(){
console.log(this.src);
var original = new Image(this.src);
console.log(original);
$("#original_w").text(original.width); // Temp, more images to be added
$("#original_h").text(original.height); // Temp, more images to be added
});
});
Console output:
http://localhost/DigitLifeAdminExtension/images/pillars-of-creation.jpg
<img width="0">

Get the width/height of the image itself, not the div it is contained within.
$(window).load(function(){
$('img.croppable').each(function(){
var img = new Image();
img.src = $(this).src;
alert(img.width);
});
});

You can remove the attributes, get the width and put the attributes in place again:
var $img = $(img);
var oldWidth = $img.attr("width");
var imgWidth = $img.removeAttr("width").width();
$img.width(oldWidth);
But I think Chris G.'s answer works well too, just making sure it will be loaded when you try to get the width:
img.onload = function() {
if (!img.complete) return; // IMG not loaded
width = img.width;
imgManipulationGoesHere();
}

Works in most up-to-date browsers and IE9.
$(window).load(function(){
$('img.croppable').each(function(){
alert(this.naturalHeight);
});
});

The working solution would be:
$(function(){
$('img.croppable').each(function () {
var original = new Image(this.src);
original.onload = function () {
alert(original.src + ': ' + original.width + 'x' +original.height);
};
});
});

Get image dimensions with Javascript before image has fully loaded

I've read about various kinds of ways getting image dimensions once an image has fully loaded, but would it be possible to get the dimensions of any image once it just started to load?
I haven't found much about this by searching (which makes me believe it's not possible), but the fact that a browser (in my case Firefox) shows the dimensions of any image I open up in a new tab right in the title after it just started loading the image gives me hope that there actually is a way and I just missed the right keywords to find it.

You are right that one can get image dimensions before it's fully loaded.
Here's a solution (demo):
var img = document.createElement('img');
img.src = 'some-image.jpg';
var poll = setInterval(function () {
if (img.naturalWidth) {
clearInterval(poll);
console.log(img.naturalWidth, img.naturalHeight);
}
}, 10);
img.onload = function () { console.log('Fully loaded'); }

The following code returns width/height as soon as it's available. For testing change abc123 in image source to any random string to prevent caching.
There is a JSFiddle Demo as well.
<div id="info"></div>
<img id="image" src="https://upload.wikimedia.org/wikipedia/commons/d/da/Island_Archway,_Great_Ocean_Rd,_Victoria,_Australia_-_Nov_08.jpg?abc123">
<script>
getImageSize($('#image'), function(width, height) {
$('#info').text(width + ',' + height);
});
function getImageSize(img, callback) {
var $img = $(img);
var wait = setInterval(function() {
var w = $img[0].naturalWidth,
h = $img[0].naturalHeight;
if (w && h) {
clearInterval(wait);
callback.apply(this, [w, h]);
}
}, 30);
}
</script>

One way is to use the HEAD request, which asks for HTTP Header of the response only. I know in HEAD responses, the size of the body is included. But I don't know if there anything available for size of images.