We Keep Coding

How do I load the image from file chooser and get it to load on the canvas so that i can edit it using Javascript?

I have been using a pixel editor called pixel paint and I wanted to create a button that allows me to load any image onto the canvas. Currently, I have been researching and testing multiple methods online and I am still struggling to get the image loaded in. Here is the code for the script.js method.
function showSelectedFile(){
var canvas = document.createElement("canvas");
var context = canvas.getContext("2d");
var img = new Image();
var file = document.getElementById("inputfile");
var name = file.value.replaceAll("\\","").replace("C:fakepath","").replace(".png","");
document.getElementById("myText").value = name;
window.URL = window.URL || window.webkitURL;
img.onload = function()
{
context.drawImage(img,0,0)
}
img.src = "/Users/angadp/Dropbox/Mac/Downloads/pixel-paint-master/" + name + ".png";
}
Also, in the script.js file I have tried to use
var canvas = document.getElementById("canvas-div")
but it gets the following error
Uncaught TypeError: canvas.getContext is not a function
In the index.html file the code is currently using <div id="canvas-div"></div>. So I am not really sure how to load the image onto the canvas that is using the div tag. Also at the beginning of the html file I am using <input id='inputfile' type='file' accept = ".png" name='inputfile' onChange='showSelectedFile()'> which makes the choose file button.
I also have a picture of pixel paint so that you would know what I am talking about.
Can you please provide me with some help on how to solve all these solutions. Thank you. I have also attached the hyperlink to the original pixel-paint so that you can download and test it.
Pixel Editor Menu for you to download and test

You can load image on change of file. Then createObjectURL (that's data:something;base64). Then load it on an image finally draw it on the <canvas>.
function loadFile(event) {
var canvas = document.querySelector("canvas");
var ctx = canvas.getContext('2d');
var dummy = document.getElementById('dummy');
dummy.src = URL.createObjectURL(event.target.files[0]);
dummy.onload = function() {
ctx.drawImage(dummy, 0, 0, 600, 300);
// Set line width
ctx.lineWidth = 10;
ctx.beginPath();
ctx.moveTo(50, 140);
ctx.lineTo(150, 60);
ctx.lineTo(250, 140);
ctx.closePath();
ctx.stroke();
// free memory
URL.revokeObjectURL(dummy.src)
dummy.parentNode.removeChild(dummy)
}
};
canvas {
width: 600px;
height: 300px;
}
<input type="file" accept="image/*" onchange="loadFile(event)">
<canvas></canvas>
<img id="dummy" />

Save Canvas to PNG for iOS

I use react and html-to-image to export HTML to images. Because Safari not working properly with the jpg/png export, I need to export HTML node to SVG (data url is generated like this : data:image/svg...).
With this string, I am creating a new Image inside a Canvas then saving canvas to .Png with method canvas.toDataURL("image/png").
Everything is working on Firefox/Chrome, but on Safari, it's not working the first time.
First Click - Just avec HTML node (no text)
Second Click - Some Images + Previous HTML Node
Third Click - Everything is working
Here is part of my function :
var canvas = document.createElement("canvas")
var ctx = canvas.getContext('2d')
var img = new Image;
setTimeout(()=>{
htmlToImage.toSvg(document.querySelector('.Banner'), {pixelRatio: RatioVal}).then((dataUrl) => {
canvas.width = 1300*RatioVal;
canvas.height = 690*RatioVal;
img.src = dataUrl;
img.onload = () => {
ctx.drawImage(img,0,0,canvas.width, canvas.height)
var Export = canvas.toDataURL("image/png");
document.body.append(Export)
var a = document.createElement('a');
a.href = Export;
a.download = window.Chara.Nom+".png";
a.click();
};
})
},600)
Do you know why I need to click on Export 3 times to have a full image ?
Is this the best way to convert SVG dataUrl to PNG Image ?
I tried many things (Blob to Png etc..) but the problem is the same on Safari.

Refresh canvas everytime I want to download a new image

i'm working on a web app where you can upload an image, put a png image over, and download the image with the sticker applied.
For that i'm using html2canvas, and it's working fine, you upload your photo, choose the png and download the new image, so far everyting is fine, but if you want to change the png and download the new image it will dowload the first image again with the first png. Im checking and im creating everytime a new canvas, but evertyme the download button uses the first canvas. How could i refresh that canvas to donwload the last one everytime?
This is the code:
<script>
const capture = () => {
const body = document.querySelector('#ImagenLista');
body && (body.id = 'CapturaPantalla');
html2canvas(document.querySelector("#CapturaPantalla")).then(canvas => {
document.body.appendChild(canvas);
}).then(() => {
var canvas = document.querySelector('canvas');
canvas.style.display = 'none';
var image = canvas.toDataURL("image/jpg").replace("image/jpg", "image/octet-stream");
var a = document.createElement("a");
a.setAttribute('download', 'YoSoyYVoyA.jpg');
a.setAttribute('href', image);
a.click();
});
};
const btn = document.getElementById('DescargaImagen');
function FuncionDescarga() {
btn.addEventListener('click', capture);
}
</script>
Thank you so much.

How can I use cropme.js to allow users upload their profile image?

This is a knowledge sharing Q&A.
Cropme is a nice JS add-on for cropping and rotating an image using visual sliders. The author provided good documentation, but building a working implementation is not as simple as it should be.
The question I want to answer is this:
I want to allow my website-users to upload their profile image. That image must be exactly 240x292 pixels. The users should be able zoom and rotate their image, then crop it to that specific size and upload it to my website. How can I do all that with cropme?
These are the requires steps:
Show an empty placeholder for the image we want the user to load.
By clicking the "Get Image" button, the user can select an image from its local files.
The selected file is loaded into memory, and presented for editing using 'cropme'. The user can use visual sliders to rotate and zoom in/out
After clicking "Crop", the user is presented with the cropped image, and can decide to save the image or to cancel.
After clicking "Save", the cropped image is uploaded to a PHP server, the modal window is closed, and the placeholder image is replaced with the link to the just-uploaded image.
So how can we do this?

A fully working demo is presented here:
https://codepen.io/ishahak/pen/XWjVzLr
I will explain some of the details, step by step.
Note: usually in my code when you see obj[0], it is simply a conversion from jQuery object into a simple JS object.
1. Showing a placeholder for the image.
We can create a real SVG image on the fly using this code:
getImagePlaceholder: function(width, height, text) {
//based on https://cloudfour.com/thinks/simple-svg-placeholder/
var svg = '\
<svg xmlns="http://www.w3.org/2000/svg" width="{w}" \
height="{h}" viewBox="0 0 {w} {h}">\
<rect fill="#ddd" width="{w}" height="{h}"/>\
<text fill="rgba(0,0,0,0.5)" font-family="sans-serif"\
font-size="30" dy="10.5" font-weight="bold"\
x="50%" y="50%" text-anchor="middle">{t}</text>\
</svg>';
var cleaned = svg
.replace(/{w}/g, width)
.replace(/{h}/g, height)
.replace('{t}', text)
.replace(/[\t\n\r]/gim, '') // Strip newlines and tabs
.replace(/\s\s+/g, ' ') // Condense multiple spaces
.replace(/'/gim, '\\i'); // Normalize quotes
var encoded = encodeURIComponent(cleaned)
.replace(/\(/g, '%28') // Encode brackets
.replace(/\)/g, '%29');
return 'data:image/svg+xml;charset=UTF-8,' + encoded;
}
2. By clicking the "Get Image" button, the user can select an image from its local files.
This process involves an input element of type "file" which has no visible appearance (we set it with the 'd-none' class), and a button element which 'clicks' it to open a dialog:
<button id="btnGetImage" class="btn btn-primary">Get Image</button>
<input class="d-none" type="file" id="fileUpload" accept="image/*" />
And the relevant code:
$('#btnGetImage').on('click', function(){
//force 'change' event even if repeating same file:
$('#fileUpload').prop("value", "");
$('#fileUpload').click();
});
$('#fileUpload').on('change', function(){
CiM.read_file_from_input(/*input elem*/this, function() {
console.log('image src fully loaded');
$('#imgModal-dialog').modal('show');
});
});
When a file is selected, the 'change' event is firing, leading us to read the file into memory.
3. The selected file is loaded into memory, and presented for editing using 'cropme'. The user can use visual sliders to rotate and zoom in/out
Our read_file_from_input mentioned above is implemented like this:
imgHolder: null,
imgHolderCallback: null,
read_file_from_input: function(input, callback) {
if (input.files && input.files[0]) {
imgHolderCallback = callback;
var reader = new FileReader();
if (!CiM.imgHolder) {
CiM.imgHolder = new Image();
CiM.imgHolder.onload = function () {
if (imgHolderCallback) {
imgHolderCallback();
}
}
}
reader.onload = function (e) {
console.log('image data loaded!');
CiM.imgHolder.src = e.target.result; //listen to img:load...
}
reader.readAsDataURL(input.files[0]);
}
else {
console.warn('failed to read file');
}
}
When the FileReader is ready, we set the src for our internal image holder, and wait for the 'load' event, which signals that the img element is ready with the new content.
We listen to that 'load' event, and when triggered we show the modal. A modal in Bootstrap has several events. We listen to the one which signals that the modal is shown, meaning that the width and set and we can plan our Cropme dimensions based on it.
update_options_for_width: function(w) {
var o = CiM.opt, //shortcut
vp_ratio = o.my_final_size.w / o.my_final_size.h,
h, new_vp_w, new_vp_h;
w = Math.floor(w * 0.9);
h = Math.floor(w / o.my_win_ratio);
o.container.width = w;
o.container.height = h;
new_vp_h = 0.6 * h;
new_vp_w = new_vp_h * vp_ratio;
// if we adapted to the height, but it's too wide:
if (new_vp_w > 0.6 * w) {
new_vp_w = 0.6 * w;
new_vp_h = new_vp_w / vp_ratio;
}
new_vp_w = Math.floor(new_vp_w);
new_vp_h = Math.floor(new_vp_h);
o.viewport.height = new_vp_h;
o.viewport.width = new_vp_w;
}
We wait for the size of the modal to be set because cropme must be set with specific viewport dimensions. At the end of our shown.bs.modal handler, we create our Cropme instance.
4. After clicking "Crop", the user is presented with the cropped image, and can decide to save the image or to cancel.
Here is the save-button handler:
$('#imgModal-btnSave').on('click', function(){
uploadImage(croppedImg[0], function(path_to_saved) {
savedImg[0].src = path_to_saved;
$('#imgModal-dialog').modal('hide');
});
});
The uploadImage function goes like this:
uploadImage: function(img, callback){
var imgCanvas = document.createElement("canvas"),
imgContext = imgCanvas.getContext("2d");
// Make sure canvas is as big as the picture (needed??)
imgCanvas.width = img.width;
imgCanvas.height = img.height;
// Draw image into canvas element
imgContext.drawImage(img, 0, 0, img.width, img.height);
var dataURL = imgCanvas.toDataURL();
$.ajax({
type: "POST",
url: "save-img.php", // see code at the bottom
data: {
imgBase64: dataURL
}
}).done(function(resp) {
if (resp.startsWith('nok')) {
console.warn('got save error:', resp);
} else {
if (callback) callback(resp);
}
});
}
It is matched with a simple PHP script which appears at the end of the HTML in the codepen. I think this answer went too long, so I'll finish here.
Good luck - have fun :)

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();
}
}