Develop Reference

Is it possible to draw a canvas thats bigger than the current screen?

I'm drawing a image to a canvas, and when doing so the image gets downscaled to the canvas(which makes it lose quality) even though the image is the same size as the canvas, thats because the img does a good job scaling down the actual img that in reality has a bigger naturalheight and naturalwidth. I know there is possible ways to make this quality better, however i have no need of actually showing this canvas to the user/no need of downscaling. Therefore am i wondering if there is any way to drawImage that is bigger than the screen and hold it somewhere? Heard someone mention a box object or a camera object somewhere but couldn't really get use of that information only.
Question, is it possible to draw a canvas bigger than the screen? in that case how?
This is the code im working with atm
var image = document.getElementById('insertedImg');
var height = $("#insertedImg").height();
var width = $("#insertedImg").width();
var c=document.getElementById("canvass");
var ctx=c.getContext("2d");
c.height=height;
c.width=width;
ctx.drawImage(image,0,0,width,height);

Use an offscreen canvas, you just need to create a new canvas and set its height and width accordingly. Then you can append it to an element or export the image as a base64 string or whatever you need.
//canvas is not visible unless appended to a DOM element
var canvas = document.createElement('canvas');
canvas.width = $("#insertedImg").height();
canvas.height = $("#insertedImg").width();
var ctx = canvas.getContext('2d');
//do the drawing, etc.
ctx.drawImage(...);
//export the image
var img = canvas.toDataURL("image/png");

Update HTML canvas width and height attributes automatically

I want to use HTML5 canvas with flexbox. I need to set canvas.width and canvas.height automatically when user resizes window. I have tried to use jQuery for it:
$(".cnvs").attr("width", $(".cnvs").width());
$(".cnvs").attr("height", $(".cnvs").height());
but it keeps increasing actual width of canvas so it almost fills entire screen. I have put it on jsfiddle - try to resize output window with separator.
Is there any reasonable way how to do it? Thanks.
Edit: Just to be clear: I don't want to fill entire screen with that canvas. I want UI where I have:
<div class="container">
<div class="control"></div>
<canvas></canvas>
<div class="control"></div>
</div>
then use flexbox to put those three elements beside eachother, while canvas will be twice as wide as the other. This works without problem, but canvas.width and canvas.height doesn't get updated, so whenever I render something onto that canvas, it is rendered as if that canvas was 320x140 px.
Edit 2: I am sorry, but (perhaps because of my poor English) I am not clear enough. I will try to explain it once again:
Actual width of canvas element is correct (even without using any JavaScript code) only by using flexbox. My problem is that although width is correct (and $(".cnvs").width() returns correct value of width), it doesn't have any "width" attribute, it is still:
<canvas>
</canvas>
and I need to provide width argument by myself (because it renders badly when it's not set). When I try to use my code or proposed:
...
var rect = canvas.parentNode.getBoundingClientRect();
canvas.width = rect.width;
canvas.height = rect.height;
...
it behaves weirdly, canvas's width keeps increasing with every resize, but too much (it erases both control divs almost immediately).

Update 2
If I understand the question correct: the canvas has a flex CSS set (not shown in the question right now). It defines the canvas to be 2x the size of the other two elements, but since the canvas is resized and not its bitmap, the drawings are stretches as well and you want the bitmap to adopt dynamically.
If so, do this change to the code -
This update will leave the CSS rules of the canvas element alone and let flexbox handle it. It will read the actual pixel size of the element and then apply it to the bitmap so that data isn't stretched:
$(window).on("resize", function() {
var cnvs = $(".cnvs")[0]; // cache canvas element
var rect = cnvs.getBoundingClientRect(); // actual size of canvas el. itself
cnvs.width = rect.width;
cnvs.height = rect.height;
// ... redraw content here ...
}
Additionally, since resizing the window can produce a lot of events, you may want to consider "debouncing" so that you only deal with the more recent resize:
var timerID;
$(window).on("resize", function() {
clearTimeout(timerID);
timerID = setTimeout(function() {
var cnvs = $(".cnvs")[0]; // cache canvas element
var rect = cnvs.getBoundingClientRect(); // actual size of canvas el. itself
cnvs.width = rect.width;
cnvs.height = rect.height;
// ... redraw content here ...
}, 180); // adjust at will
}
This will delay the resizing/redrawing until 180ms has passed.

You don't even have to load jQuery, it is simple:
var canvas = document.querySelector("canvas");
window.addEventListener("resize", function(){
canvas.setAttribute("width", window.innerWidth);
canvas.setAttribute("height", window.innerHeight)
})

You have to add a listener to the resize event on the window object.
If your looking for a jquery solution.
$( window ).resize(function() {
$(".cnvs").attr("width", $(window).width());
$(".cnvs").attr("height", $(window).height());
});
This should work just fine.

Highcharts Image Renderer Auto Height

I am trying to put up a logo on the top left corner of the graph and the below code is working fine, but what i wanted to know is is their any direct way by which i can make either height or width auto like we do in CSS?
function (chart) {
chart.renderer.image("http://i.imgur.com/mX5qRdP.png", 5,5, 30, 30).add();
}
I know i can do it by calculating height and width this way..
var img = new Image();
img.onload = function() {
alert(this.width + 'x' + this.height);
}
img.src = 'http://www.google.com/intl/en_ALL/images/logo.gif';
But is their any more sophisticated way?

Highcharts is an SVG librarie, and the SVG 1.1 specification requires the width and height attributes for the <image> element.
See the documentation to see the attributes definitions.
What i wanted to know is their any direct way by which i can make either height or width auto like we do in CSS?
Actually, I don't think there is a way to have the automatic size like css because SVG needs a number for the attributes width and height of the <image> element.

html image id and canvas

Hi there I have a simple question I can'[t seem to find the answer to on google. I'm trying to draw an image on a canvas. I originally used the "new" constructor ( ballPic = new Image(); ballPic.src = "ball.png" ) which worked when drawing on my canvas, but I needed to do some scaling and wasn't sure if I could attach a css id to the object. So I instead tried to use the image tag and did the rest in css.
However using a variable that way doenst seem to work with my canvas' drawing:
ballPic = '<img id="soccerBall">';
var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
ctx.drawImage(BallPic, -25, -25);
Is this because assigning a variable like ballPic = is not the same as being the element itself like when using the constructor? How would I pass it other than attaching it to the document and using getElementbyID?

You can keep using the Image constructor and still scale the image. There's another method overload of the drawImage function:
From MDN:
The second variant of the drawImage() method adds two new parameters and lets us place scaled images on the canvas.
drawImage(image, x, y, width, height)
This adds the width and height parameters, which indicate the size to which to scale the image when drawing it onto the canvas.
I would recommend you check out that page, it has a lot of good information, like
Using data: urls
Handling image loading
Loading still frames from videos
Slicing
Examples gallore

Create an image, handle the onload event, in which you update the canvas size to the scaled size of the image, then drawImage with a scale.
var scale = 2 ;
var ballPic = new Image();
ballPic.onload = function drawImage() {
var c=document.getElementById("myCanvas");
c.width = ballPic.width * scale ;
c.height = ballPic.height * scale ;
var ctx=c.getContext("2d");
ctx.scale(scale, scale) ;
ctx.drawImage(ballPic, 0, 0);
};
ballPic.src =
'http://melinabeachturtlehatchery.files.wordpress.com/2010/07/turtle4.jpg';
the fiddle is here :
http://jsbin.com/etemox/1/edit

Which jQuery method of creating a canvas of a certain size has the best performance?

What I'd like to do is create a 15 by 15 pixel sized canvas with jQuery and I am looking for an elegant way to do it.
I currently create a canvas with jQuery like this:
var canvasNode = $('<canvas />', {
style:'display:block',
width:15,
});
// canvasNode[0].width=15;
canvasNode[0].height=15;
An oddity is that the width:15 in that has no effect while the currently commented out line below does what I'd like to do. I also tried style:'display:block;width:15px;' but while that displays the canvas at 15px width the canvas itself stays at its large default size so its just being scaled so that's not what I seek.

In case you are really worried about performance, this is the fastest way (untested, but I'm sure it is):
var canvas = document.createElement("canvas");
canvas.width = 15;
canvas.height = 15;
That is, no jQuery at all.

Note that sending in an object with a width property will set the css width to 15px (basically just scaling the canvas), the canvas will still be created with the default number of pixels in width if no width attribute is specified, which is usually 300 pixels.
Just set the width and height attributes:
$('<canvas />', {
style:'display:block'
}).attr('width', 15).attr('height', 15);