I am trying to show previews of uploaded images in a canvas. The preview should be a square version of image.
What I have:
var img = new Image;
img.src = imageSrc;
var c = document.getElementById('file-preview-' + data.response.id);
var ctx = c.getContext("2d");
img.onload = function() {
ctx.drawImage(img, 0, 0);
};
And the preview:
So how can I draw on the canvas a 150x150 square with maintained ratio cropped version of the image?
For example for this image:
I should get:
Here's a method that yields precisely the result you desire, cropped, resized and centered (with commented out lines that yield a left based cropping instead)...
var ctx;
function init(event) {
ctx = document.getElementById('canvas').getContext('2d');
// Your preview is actually 120x120,
// but I've stuck with the textual description of
// your requirements here.
ctx.canvas.width = 150;
ctx.canvas.height = 150;
loadBackground('http://i.stack.imgur.com/PCKEo.png');
}
function loadBackground(path) {
var img = new Image();
img.onload = drawBackground;
img.src = path;
}
function drawBackground(event) {
var img = event.target;
var imgSize = Math.min(img.width, img.height);
// The following two lines yield a central based cropping.
// They can both be amended to be 0, if you wish it to be
// a left based cropped image.
var left = (img.width - imgSize) / 2;
var top = (img.height - imgSize) / 2;
//var left = 0; // If you wish left based cropping instead.
//var top = 0; // If you wish left based cropping instead.
ctx.drawImage(event.target, left, top, imgSize, imgSize, 0, 0, ctx.canvas.width, ctx.canvas.height);
}
window.addEventListener('load', init, false);
<canvas id="canvas"></canvas>
Based on information from this question: SO Question
I was able to modify what was done to create a square cropped image in canvas:
var img = new Image;
img.src = "http://cdn.bmwblog.com/wp-content/uploads/2016/02/M-Performance-Parts-BMW-M2-3.jpg"; //Or whatever image source you have
var c= document.getElementById('file-preview');
var ctx=c.getContext("2d");
img.onload = function(){
ctx.drawImage(img, img.width/2, img.height/2, img.width, img.height, 0, 0, img.width, img.height);
};
You just have to modify the arguments you are passing to the drawImage function as well as add some more.
You can see a fiddle here: https://jsfiddle.net/4d93pkoa/3/
Remember that the first two parameters specify the image's top left coordinates within the canvas element.
Remember to set the width and height of the canvas element in HTML to a square shape.
Related
I created a new image but I'm trying to resize it and add some transformations to it. How ever, they are not taking effect.
Example: https://jsfiddle.net/chung9ey/3/
img.onload = function(){
img.style.width = "500";
img.style.height = "300";
img.style.transform = "perspective(500px) rotateZ(30deg)";
context.drawImage(img, 0 ,0);
}
Styles change properties, not attributes. In order to change the actual attributes you would need to use
img.height = 300;
//or by native API
img.setAttribute("height",300);
and so on for each attribute you wanted to change. Note that attributes are part of the html element and not necessarily part of the css definition (more on that here: https://www.w3.org/TR/CSS21/cascade.html#preshint).
Try using this.
document.getElementById("imageID").style.height="300px";
document.getElementById("imageID").style.width="500px";
That should change the element's style width and height to what you want.
In the HTML script, it'd be
<img src="source.jog" id="imageID"/>
Based on this Stack Overflow answer, change your JS to:
var img = new Image();
var canvas = document.getElementById("hello");
var context = canvas.getContext("2d");
img.onload = function(){
context.save(); // Saves current canvas state (includes transformations)
context.rotate(30); // This rotates canvas context around its top left corner...
context.translate(-275, 125); // ...so you need to make a correction.
context.drawImage(img, 0, 0, 500, 300);
context.restore(); // Restore canvas state
};
img.src = "https://www.enterprise.com/content/dam/global-vehicle-images/cars/CHRY_200_2015.png";
This essentially rotates the canvas's contents after the image is drawn on it.
Part of the image is off-canvas as a result of this rotation, so you may also want to scale the canvas to fit the rotated image.
https://jsfiddle.net/Lcyksjoz/
i would change the image size in the canvas and then manipulating the canvas through id
var img = new Image(100, 100);
var canvas = document.getElementById("hello");
var context = canvas.getContext("2d");
var width = 500;
var height = 300;
img.onload = function(){
img.style.transform = "perspective(200px) rotateZ(30deg)";
context.drawImage(img, 0 ,0, width,height);
}
img.src = "https://www.enterprise.com/content/dam/global-vehicle-images/cars/CHRY_200_2015.png";
document.getElementById("hello").style.width="300px";
https://jsfiddle.net/chung9ey/27/
with this code I try to update a canvas with a drawn image when imageUpdated is true.
I use a timetag so the image isnt loaded from the browser cache.
But when i use timetags the canvas stays empty.
It works without the timetags.
var imageUpdated = true;
if(imageUpdated)
{
imageUpdated = false;
var heightImg = new Image;
heightImg.src = '/path/to/image.png?' + new Date().getTime().toString();
this.canvas = $('<canvas />')[0];
this.canvas.width = this.width;
this.canvas.height = this.height;
this.canvas.getContext('2d').drawImage(heightImg, 0, 0, this.width, this.height);
}
/*rest of event happens here*/
Thanks!
Probably it's because you're drawing the image before it is loaded.
I guess that's also the reason it works without the timetag, it's already in cache so can instantly be drawn.
A solution would be to draw after the image is loaded. So, add an eventListener on the image:
image.addEventListener('load', callback);
Within the callback, draw the image on the canvas.
For example:
// add eventlistener
heightImg.addEventListener('load', function(e) {
var width = heightImg.width;
var height = heightImg.height;
var canvas = document.querySelector('canvas');
canvas.width = width;
canvas.height = height;
canvas.getContext('2d').drawImage(heightImg, 0, 0, width, height);
});
// trigger the loading
heightImg.src = url + '?time=' + new Date().getTime().toString();
And a Fiddle
So I am creating a cordova app where I take a photo from the iphone library, draw it to canvas and add another image to it in order to save it as one photo. So far the photo I draw from the iphone photo library gets drawn without problems to the canvas, however the second image doesn't.
When I load the second image, it first gets added to a div with absolute positioning in order to move it to wherever I want. After that I get the actual image it's source and it's positions and try to draw it to canvas. The drawing of the second image happens when I call a method that also performs the canvas2ImagePlugin it's functions. In the end only the first photo without the second image gets saved.
The draw image to canvas function:
function drawImage(image_source, dx, dy)
{
var canvas = document.getElementById('Photo');
var image = new Image();
image.src = image_source;
image.onload = function() {
c=canvas.getContext("2d");
c.canvas.width = window.innerWidth;
c.canvas.height = window.innerHeight;
c.drawImage(image,dx,dy, window.innerWidth, window.innerHeight);
}
}
The method for drawing the second image and saving it:
function saveImage()
{
var img = $('.ObjectImage').attr('src', $('img:first').attr('src'));
var imagePosition = $('.ObjectImage').find('img:first').position();
drawImage(img, imgPosition.left, imgPosition.top);
window.canvas2ImagePlugin.saveImageDataToLibrary(
function(msg){
console.log(msg);
},
function(err){
console.log(err);
},
document.getElementById('Photo')
);
alert("Image saved");
}
The window.innerWidth, window.innerHeight on the canvas is done to get the canvas in full screen of the parent div.
EDIT to the comment:
function drawImage(image_source, dx, dy)
{
var canvas = document.getElementById('Photo');
var image = new Image();
image.onload = function() {
c=canvas.getContext("2d");
c.canvas.width = window.innerWidth;
c.canvas.height = window.innerHeight;
c.drawImage(image,dx,dy, window.innerWidth, window.innerHeight);
}
image.src = image_source;
}
Still not working
The drawImage function works asynchronously, it starts loading an image and exits immediately. Then, when the image loads, the canvas is updated. If you run something like:
drawImage('test.jpg',0,0);
drawImage('test2.jpg',0,0);
you will get both images updating the canvas at approximately the same time and only one will appear.
Also, what wolfhammer said is correct. If you set the size of the canvas, you clear it, so drawing one image after the other, even if they are smaller sizes and should both appear, will only show the last one. Check this link on how to solve it: Preventing Canvas Clear when Resizing Window
Further more, you are drawing all images with the width and height of the window, which doesn't make sense. Probably you want to use the width and height of the image (so this.width instead of window.innerWidth)
When you set the width and height of the canvas the data on "Photo" is cleared. I've provide a resize function if resizing is really needed.
function drawImage(image_source, dx, dy)
{
var canvas = document.getElementById('Photo');
var image = new Image();
image.src = image_source;
image.onload = function() {
c=canvas.getContext("2d");
//c.canvas.width = window.innerWidth;
//c.canvas.height = window.innerHeight;
c.drawImage(image,dx,dy, window.innerWidth, window.innerHeight);
}
}
var can = document.getElementById('can');
var ctx = can.getContext('2d');
ctx.fillStyle = "red";
ctx.beginPath();
ctx.moveTo(20, 90);
ctx.lineTo(50, 10);
ctx.lineTo(80, 90);
ctx.lineTo(10, 40);
ctx.lineTo(90, 40);
ctx.lineTo(20, 90);
ctx.fill();
var btn = document.getElementById('btnResize');
btn.addEventListener('click', function() {
resize(can, can.width * 2, can.height * 2);
});
function resize(can, w, h) {
var ctx = can.getContext('2d');
// copy
var can2 = document.createElement('canvas');
var ctx2 = can2.getContext('2d');
can2.width = can.width;
can2.height = can.height;
ctx2.drawImage(can, 0, 0);
// resize
can.width = w;
can.height = h;
ctx.drawImage(can2, 0, 0, can2.width, can2.height, 0, 0, w, h);
}
#can {
border:1px solid red;
}
<button id='btnResize'>Size x 2</button><br/>
<canvas id="can" width="100" height="100"></canvas>
I'm basically trying to get the selected image file from a input dialog and set it to a canvas that's in my HTML. However, the image gets cropped and only a portion of the image is shown.
Javascript:
function onSS1Change(file) {
var ctx = document.getElementById('canvas').getContext('2d');
var img = new Image;
img.onload = function () {
ctx.drawImage(img, 20, 20);
}
img.src = URL.createObjectURL(file.target.files[0]);
}
HTML:
<input id="ss1-inputdiag" type="file" onchange="onSS1Change(event)" />
Fiddle: http://jsfiddle.net/tdy9tqfh/
I need to get the original height and width
What am I doing wrong?
jsFiddle : http://jsfiddle.net/CanvasCode/tdy9tqfh/2/
Just update the canvas height and width to fit the image, also you were drawing your image at position x 20 and y 20 so all your images will be slightly cut off at the right side and bottom.
var input = document.getElementById('input');
input.addEventListener('change', handleFiles);
function handleFiles(e) {
var c = document.getElementById('canvas');
var ctx = c.getContext('2d');
var img = new Image;
img.src = URL.createObjectURL(e.target.files[0]);
img.onload = function() {
c.width = img.width;
c.height = img.height;
ctx.drawImage(img, 0,0);
alert('the image is drawn');
}
}
I'm trying to load an image from a URL into a HTML canvas at a 1:1 scale. I load the image, and set the canvas DOM element to the appropriate dimensions, but for some reason the image in the canvas is significantly upscaled and therefore only the top left hand corner is drawn.
This is demonstrated by the following JSFiddle: http://jsfiddle.net/KdrYr/1/
var img = new Image();
var cv = document.getElementById('thecanvas');
img.src = 'http://www.photographyblogger.net/wp-content/uploads/2009/12/Picture-in-a-picture4.jpg';
img.onload = function() {
var ctx = cv.getContext('2d');
cv.style.width = img.width + 'px';
cv.style.height = img.height + 'px';
ctx.drawImage(img, 0, 0);
};
For example, I'm trying to draw this (sorry about the big images :/)
But end up with this
What could be causing this?
You need to assign the canvas actual width and height, not via its style:
cv.width = img.width;
cv.height = img.height;
Live test case.
As for the why, well, it's explained already here.