We Keep Coding

Displaying preloaded image (p5.js)

I'm trying a basic display of a preloaded image with p5.js library (instantiation mode):
var sketch = function(p) {
var fondo;
p.preload = function() {
fondo = p.loadImage('app/themes/mrg/dist/images/tramas/example.jpg');
};
var viewportWidth = $(window).width();
p.setup = function(){
canvas = p.createCanvas(viewportWidth, 200);
canvas.background(255);
canvas.image(fondo, 0, 0);
};
};
new p5(sketch);
The canvas was created but no image is there.
Here is a working example:
https://stage.margenesdelarte.org/
The canvas is at the end of the page (with white background) but no image is rendered inside.
Image path is right, since there is no error in the console and it can be reached in its place:
https://stage.margenesdelarte.org/app/themes/mrg/dist/images/tramas/example.jpg
What is wrong, and how can I display this image? Thanks!

That's correct version? (I used BASE64 because I didn't want to run a local server)
var sketch = function(p) {
var fondo;
p.preload = function() {
fondo = p.loadImage("data:image/gif;base64,R0lGODdhMAAwAPAAAAAAAP///ywAAAAAMAAwAAAC8IyPqcvt3wCcDkiLc7C0qwyGHhSWpjQu5yqmCYsapyuvUUlvONmOZtfzgFzByTB10QgxOR0TqBQejhRNzOfkVJ+5YiUqrXF5Y5lKh/DeuNcP5yLWGsEbtLiOSpa/TPg7JpJHxyendzWTBfX0cxOnKPjgBzi4diinWGdkF8kjdfnycQZXZeYGejmJlZeGl9i2icVqaNVailT6F5iJ90m6mvuTS4OK05M0vDk0Q4XUtwvKOzrcd3iq9uisF81M1OIcR7lEewwcLp7tuNNkM3uNna3F2JQFo97Vriy/Xl4/f1cf5VWzXyym7PHhhx4dbgYKAAA7");
};
var viewportWidth = 500;
p.setup = function(){
var canvas = p.createCanvas(viewportWidth, 200);
canvas.image(fondo, 0, 0); // doesn't work
p.image(fondo, 0, 0); // works fine
console.log(p.image, canvas.image); //there are different functions
};
};
new p5(sketch);
https://codepen.io/anon/pen/yPENXx?editors=1111
Explanation:
Both p and canvas has a image function but there are different image functions. You have to use p.image(). I think canvas.image() is has some relations with https://p5js.org/reference/#/p5.Image, but that's only my assumptions.

Is your file being localhosted? For p5 to access local files such as images, it needs to be localhosted... I recommend apache

Execute Function After Canvas toDataURL() Function is Complete

I'm converting images to base64 using canvas. What i need to do is convert those images and then show the result to the user (original image and base64 version). Everything works as expected with small images, but when i try to convert large images (>3MB) and the conversion time increases, the base64 version is empty.
This might be is caused because the result is shown before the toDataURL() function is completed.
I need to show the result after all the needed processing has ended, for testing purposes.
Here's my code:
var convertToBase64 = function(url, callback)
{
var image = new Image();
image.onload = function ()
{
//create canvas and draw image...
var imageData = canvas.toDataURL('image/png');
callback(imageData);
};
image.src = url;
};
convertToBase64('img/circle.png', function(imageData)
{
window.open(imageData);
});
Even though i'm using image.onload() with a callback, i'm unable to show the result after the toDataURL() has been processed.
What am i doing wrong?
UPDATE: I tried both the solutions below and they didn't work. I'm using AngularJS and Electron in this project. Any way i can force the code to be synchronous? Or maybe some solution using Promises?
UPDATE #2: #Kaiido pointed out that toDataURL() is in fact synchronous and this issue is more likely due to maximum URI length. Since i'm using Electron and the image preview was for testing purposes only, i'm going to save the file in a folder and analise it from there.

Your code seems absolutely fine. Not sure why isn't working you. Maybe, there are some issues with your browser. Perhaps try using a different one. Also you could use a custom event, which gets triggered when the image conversion is competed.
// using jQuery for custom event
function convertToBase64(url) {
var image = new Image();
image.src = url;
image.onload = function() {
var canvas = document.createElement('canvas');
canvas.width = image.width;
canvas.height = image.height;
var ctx = canvas.getContext('2d');
ctx.drawImage(image, 0, 0);
var imageData = canvas.toDataURL();
$(document).trigger('conversionCompleted', imageData);
};
};
convertToBase64('4mb.jpg');
$(document).on('conversionCompleted', function(e, d) {
window.open(d);
});

This approach might work for you. It shows the image onscreen using the native html element, then draws it to a canvas, then converts the canvas to Base64, then clears the canvas and draws the converted image onto the canvas. You can then scroll between the top image (original) and the bottom image (converted). I tried it on large images and it takes a second or two for the second image to draw but it seems to work...
Html is here:
<img id="imageID">
<canvas id="myCanvas" style="width:400;height:400;">
</canvas>
Script is here:
var ctx;
function convertToBase64(url, callback)
{
var image = document.getElementById("imageID");
image.onload = function() {
var canvas = document.getElementById("myCanvas");
canvas.width = image.naturalWidth;
canvas.height = image.naturalHeight;
ctx = canvas.getContext("2d");
ctx.drawImage(image,0,0);
var imageData = canvas.toDataURL('image/png');
ctx.fillStyle ="#FFFFFF";
ctx.fillRect(0,0,canvas.width,canvas.height);
callback(imageData);
};
image.src = url;
};
var imagename = 'images/bigfiletest.jpg';
window.onload = function () {
convertToBase64(imagename, function(imageData) {
var myImage = new Image();
myImage.src = imageData;
ctx.drawImage(myImage,0,0);
});
}
Note that I also tried it without the callback and it worked fine as well...

Using Image instead of Canvas

I have a Image and I want to paint on top of it some square. But I keep getting undefined function on getContext('2d'). I must add that the var img is an image which is already loaded on the page, I'm trying to interpret it as a canvas since I am using another script which lets to select areas on the image and if I use a canvas the script will not work. So in the case where I can not interpret a image as a canvas what would you suggest?
Js function
function drawInput(dx1,dy1,dx2,dy2) {
var img = document.getElementById('home:tempImg');
var canvas = img;
console.log(canvas);
var context = canvas.getContext('2d');
var imageObj = new Image();
imageObj.onload = function() {
context.drawImage(imageObj, dx1, dy1,dx2-dx1,dy2-dy1);
};
imageObj.src = 'images/selected.png';
}
HTML
<h:body>
<h:form onsubmit="#{getComponents.getAllComponents()}" id="home">
<div>
<p:graphicImage id="tempImg" rendered="true" value="#{imageView.selectedImg}">
</p:graphicImage>
</div>
</h:form>
</h:body>
<script type="text/javascript">
var myJSONStr ='{ "area" : #{areaInputView.areaListString}}';
console.log(myJSONStr);
var json = JSON.parse(myJSONStr);
//console.log(json.area[1].x1);
for(var i=0;myJSONStr.length >i ; i++) {
console.log(json.area[i].x1, json.area[i].y1, json.area[i].x2, json.area[i].y2);
drawInput(json.area[i].x1, json.area[i].y1, json.area[i].x2, json.area[i].y2);
};
</script>
</html>

By leveraging custom JS 'classes' (of the type app.Image in this case), we can build a pretty neat wrapper that allows us to draw images dynamically based on other instances we have kept track of.
Check out this Codepen for a working example.
window.app = window.app || {};
app.Canvas = document.getElementById('myCanvas').getContext('2d');
app.Image = function(source, x, y) {
this.x = x;
this.y = y;
this.data = new Image();
this.data.addEventListener('load', this.draw.bind(this));
this.data.src = source;
};
app.Image.prototype.draw = function() {
app.Canvas.drawImage(this.data, this.x, this.y);
};
app.Image.prototype.getImageBounds = function() {
return {
height: this.data.height,
width: this.data.width
}
};
var myImage = new app.Image('http://placehold.it/250x250', 10, 10);
var mySecondImage = new app.Image('http://placesheen.com/100/100', myImage.x + 10, myImage.y + 10);
The most important line is the last one. Notice how we're initializing a new app.Image with x and y coordinates relative to the first image. By using a custom wrapper class that keeps track of this information, we're able to easily access the necessary data that we need in a variety of circumstances.
I hope this helps to get you on the right track! Let me know if you have any questions about the code, and I'll be glad to explain.

How can I change out an image using CamanJS?

I've got multiple images, and I'd like to load them each into a single <canvas> element at different points in time and then manipulate them using CamanJS. I can get the first image to appear like this:
Caman('#canvas-element', '/images/one.jpg');
But then when I subsequently try to update that same element using the following code, it does not work.
Caman('#canvas-element', '/images/two.jpg');
Is there some way to reset/clear/flush the canvas and load new image data into it, or do I really need to create separate <canvas> elements for each image I want to load? I'd prefer a single element because I don't want to eat up all the memory.

Remove the Caman attribute (data-caman-id) from the IMG or CANVAS element, change the image, and then re-render Caman.
document
.querySelector('#view_image')
.removeAttribute('data-caman-id');
const switch_img = '/to/dir/img.png';
Caman("#view_image", switch_img, function() {
this.render();
});

Hope followed code can help others who have same require.
function loadImage(source) {
var canvas = document.getElementById('image_id');
var context = canvas.getContext('2d');
var image = new Image();
image.onload = function() {
context.drawImage(image, 0, 0, 960, 600);
};
image.src = source;
}
function change_image(source) {
loadImage(source);
Caman('#image_id', source, function () {
this.reloadCanvasData();
this.exposure(-10);
this.brightness(5);
this.render();
});
}

Just figured this one out with a lot of trial and error and then a duh moment!
Instead of creating my canvas directly in my html, I created a container and then just did the following:
var retStr = "<canvas id=\"" + myName + "Canvas\"></canvas>";
document.getElementById('photoFilterCanvasContainer').innerHTML = retStr;
Caman("#" + myName + "Canvas", myUrl, function() {
this.render();
});
You want the canvas id to be unique each time you access the Caman function with a new image.

Display Image using canvas in JavaScript/jQuery

I have the following code :
function createImage(source) {
var pastedImage = new Image();
pastedImage.onload = function() {
document.write('<br><br><br>Image: <img src="'+pastedImage.src+'" height="700" width="700"/>');
}
pastedImage.src = source;
}
Here I am displaying the image through html image tag which I wrote in document.write and provide appropriate height and width to image.
My question is can it possible to displaying image into the canvas instead of html img tag? So that I can drag and crop that image as I want?
But how can I display it in canvas?
Further I want to implement save that image using PHP but for now let me know about previous issue.

Try This
var ctx = document.getElementById('canvas').getContext('2d');
var img = new Image(); // Create new img element
img.onload = function(){
// execute drawImage statements here This is essential as it waits till image is loaded before drawing it.
ctx.drawImage(img , 0, 0);
};
img.src = 'myImage.png'; // Set source path
Make sure the image is hosted in same domain as your site. Read this for Javascript Security Restrictions Same Origin Policy.
E.g. If your site is http://example.com/
then the Image should be hosted on http://example.com/../myImage.png
if you try http://facebook.com/..image/ or something then it will throw security error.

Use
CanvasRenderingContext2D.drawImage.
function createImage(source) {
var ctx = document.getElementById('canvas').getContext('2d');
var pastedImage = new Image();
pastedImage.onload = function(){
ctx.drawImage(pastedImage, 0, 0);
};
pastedImage = source;
}
Also MDN seems to be have nice examples.