Develop Reference

Drawing an SVG dynamically using javascript

I'm trying to draw an isoceles triangle with it's top vertex in the middle of the screen.
I want to use JavaScript as screen sizes of different users can be different and hence, center of the screen must first be found out.
Here is my code:
function drawRect(){
var w = $(document).width();
var h = $(window).height();
var halfh = h/2;
var halfw = w/2;
var svg = document.createElement("svg");
var poly = document.createElement("polygon");
svg.setAttribute("style", "position: fixed;");
svg.setAttribute("height", ""+h);
svg.setAttribute("width", ""+w);
poly.setAttribute("points", ""+halfw+","+halfh+" 0,"+h+" "+w+","+h);
poly.setAttribute("style", "fill:lime;stroke:purple;stroke-width:1");
svg.appendChild(poly);
var svgplace = document.getElementById("carpet");
svgplace.appendChild(svg);
}
No triangle appears on the screen. But, if I open the 'Inspect Element' console on chrome, and I modify the created html element slightly, it appears! (Any kind of small mod. Like adding a space in the middle somewhere)
Please help!
Thanks in advance

You need to be using
document.createElementNS("http://www.w3.org/2000/svg", "polygon");
SVG is in its own namespace aside from HTML. Therefore, you need to create elements that are in the SVG namespace using createElementNS.
Consider the following example that works in Chrome and Firefox
var newItem = document.createElementNS("http://www.w3.org/2000/svg", "circle");
newItem.setAttribute("cx", ((16 * 1) + 8));
newItem.setAttribute("cy", "50%");
newItem.setAttribute("r", 4);
newItem.setAttribute("fill", "#333333");
document.getElementById("target").appendChild(newItem);
<svg id="target">
</svg>

Get pixel length of String in Svg

I'm currently working with SVG. I need to know the string length in pixels in order to do some alignment. How can I do to get the length of a string in pixel ?
Update: Thanks to nrabinowitz. Based on his help, I can now get the length of dynamic-added text. Here is an example:
<svg id="main"
xmlns="http://www.w3.org/2000/svg"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="1.1"
width="1020"
height="620"
viewBox="0 0 1020 620"
onload="startup(evt)">
<script>
<![CDATA[
var startup = function (evt) {
var width;
var svgNS = "http://www.w3.org/2000/svg";
var txtNode = document.createTextNode("Hello");
text = document.createElementNS(svgNS,"text");
text.setAttributeNS(null,"x",100);
text.setAttributeNS(null,"y",100);
text.setAttributeNS(null,"fill","black");
text.appendChild(txtNode);
width = text.getComputedTextLength();
alert(" Width before appendChild: "+ width);
document.getElementById("main").appendChild(text);
width = text.getComputedTextLength();
alert(" Width after appendChild: "+ width)
document.getElementById("main").removeChild(text);
}
//]]>
</script>
</svg>

I've been wondering this too, and I was pleasantly surprised to find that, according to the SVG spec, there is a specific function to return this info: getComputedTextLength()
// access the text element you want to measure
var el = document.getElementsByTagName('text')[3];
el.getComputedTextLength(); // returns a pixel integer
Working fiddle (only tested in Chrome): http://jsfiddle.net/jyams/

Having read various similar threads with interest and benefitted from some of the ideas, I've created a page which compares three of the Javascript methods side-by-side. I've noted results in
IE9
Firefox 29.0.1 and
Chrome 34.0.1847.131 m
You can load it in your browser and see what works for you:
http://bl.ocks.org/MSCAU/58bba77cdcae42fc2f44.

converting Div to Canvas options [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();
}
}

svg appending text element - gives me wrong width

i'm appending a text element to a svg via javascript. After appending i wanna set x and y coordinate, however, it returns me the wrong width of the text element when using it to calculate x.
Interesting:
In Chrome, when actualize the page via F5 or button it returns wrong width, when pressing enter in the adress bar, the width is right - strange!
Here is the small code:
var capt = document.createElementNS("http://www.w3.org/2000/svg", "text");
// Set any attributes as desired
capt.setAttribute("id","capt");
capt.setAttribute("font-family","Righteous");
capt.setAttribute("font-size","30px");
capt.setAttribute("fill", "rgb(19,128,183)");
var myText = document.createTextNode(this.options.captTxt);
capt.appendChild(myText);
this.elements.jSvgElem.append(capt);
capt.setAttribute("x", this.options.windowWidth-this.options.spacer-document.getElementById("capt").offsetWidth);
capt.setAttribute("y", this.options.captY+$('#capt').height());

OK, the problem seems to be that the browser doesn't calculate the correct width when using an other font. Not setting a font results in a correct width.
I solved the problem by setting the reference point ("alignment-point") to the upper right corner ot the text element by setting attributes:
capt.setAttribute("text-anchor", "end");
capt.setAttribute("alignment-baseline", "hanging");
This way i do not have to subtract the width and add the height of the element!

There is a bug:http://code.google.com/p/chromium/issues/detail?id=140472
it just pre init some functions that calculates text width so you should call this function before(i'm sure that there is several extra lines that can be deleted):
fixBug = function () {
var text = makeSVG("text", { x: 0, y: 0, fill: "#ffffff", stroke: '#ffffff'});
text.textContent = "";
var svg = $("svg")[0];
svg.appendChild(text);
var bbox = text.getBBox();
var Twidth = bbox.width;
var Theight = bbox.height;
svg.removeChild(text);
}
$("svg") - Jquery selector

Changing source of image with an image of different size, won't resize in IE

I'm trying to create a very simple gallery using javascript. There are thumbnails, and when they're clicked the big image's source gets updated. Everything works fine, except when I try it in IE the images' size stays the same as the inital image's size was. Let's say initial image is 200x200 and I click on a thumbnail of a 100x100 image, the image is displayed but it is streched to 200x200. I don't set any width or height values, so I guess the browser should use image's normal size, and so does for example FF.
here's some code:
function showBigImage(link)
{
var source = link.getAttribute("href");
var bigImage = document.getElementById("bigImage");
bigImage.setAttribute("src", source);
return false; /* prevent normal behaviour of <a> element when clicked */
}
and html looks like this:
<ul id="gallery">
<li>
<a href="images/gallery/1.jpg">
<img src="images/gallery/1thumb.jpg">
</a>
</li>
(more <li> elements ...)
</ul>
the big image is created dynamically:
function createBigImage()
{
var bigImage = document.createElement("img");
bigImage.setAttribute("id", "bigImage");
bigImage.setAttribute("src", "images/gallery/1.jpg");
var gal = document.getElementById("gallery");
var gal_parent = gal.parentNode;
gal_parent.insertBefore(bigImage, gal);
}
There's also some code setting the onclick events on the links, but I don't think it's relevant in this situaltion. As I said the problem is only with IE. Thanks in advance!

Sounds like IE is computing the width and height attributes for #bigImage when it is created and then not updating them when the src is changed. The other browsers are probably noting that they had to compute the image dimensions themselves so they recompute them when the src is changed. Both approaches are reasonable enough.
Do you know the proper size of the image inside showBigImage()? If you do, then set the width and height attributes explicitly when you change the src:
function showBigImage(link) {
var source = link.getAttribute("href");
var bigImage = document.getElementById("bigImage");
bigImage.setAttribute("src", source);
bigImage.setAttribute("width", the_proper_width);
bigImage.setAttribute("height", the_proper_height);
return false;
}
If you don't know the new dimensions then change showBigImage() to delete #bigImage and create a new one:
function createBigImage(src) {
var bigImage = document.createElement("img");
bigImage.setAttribute("id", "bigImage");
bigImage.setAttribute("src", src || "images/gallery/1.jpg");
var gal = document.getElementById("gallery");
gal.parentNode.insertBefore(bigImage, gal);
}
function showBigImage(link) {
var bigImage = document.getElementById("bigImage");
if(bigImage)
bigImage.parentNode.removeChild(bigImage);
createBigImage(link.getAttribute("href"););
return false;
}