I want to load a PNG image encoded in Base64 to canvas element. I have this code:
<html>
<head>
</head>
<body>
<canvas id="c"></canvas>
<script type="text/javascript">
var canvas = document.getElementById("c");
var ctx = canvas.getContext("2d");
data = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAIAAAACDbGyAAAAAXNSR0IArs4c6QAAAAlwSFlzAAALEwAACxMBAJqcGAAAAAd0SU1FB9oMCRUiMrIBQVkAAAAZdEVYdENvbW1lbnQAQ3JlYXRlZCB3aXRoIEdJTVBXgQ4XAAAADElEQVQI12NgoC4AAABQAAEiE+h1AAAAAElFTkSuQmCC";
ctx.drawImage(data, 0, 0);
</script>
</body>
</html>
In Chrome 8 I get the error: Uncaught TypeError: Type error
And in Firefox's Firebug this: "The type of an object is incompatible with the expected type of the parameter associated to the object" code: "17"
In that base64 is 5x5px black PNG square that I have made in GIMP and turn it to base64 in GNU/Linux's program base64.
By the looks of it you need to actually pass drawImage an image object like so
var canvas = document.getElementById("c");
var ctx = canvas.getContext("2d");
var image = new Image();
image.onload = function() {
ctx.drawImage(image, 0, 0);
};
image.src = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAIAAAACDbGyAAAAAXNSR0IArs4c6QAAAAlwSFlzAAALEwAACxMBAJqcGAAAAAd0SU1FB9oMCRUiMrIBQVkAAAAZdEVYdENvbW1lbnQAQ3JlYXRlZCB3aXRoIEdJTVBXgQ4XAAAADElEQVQI12NgoC4AAABQAAEiE+h1AAAAAElFTkSuQmCC";
<canvas id="c"></canvas>
I've tried it in chrome and it works fine.
Jerryf's answer is fine, except for one flaw.
The onload event should be set before the src. Sometimes the src can
be loaded instantly and never fire the onload event.
(Like Totty.js pointed out.)
var canvas = document.getElementById("c");
var ctx = canvas.getContext("2d");
var image = new Image();
image.onload = function() {
ctx.drawImage(image, 0, 0);
};
image.src = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAIAAAACDbGyAAAAAXNSR0IArs4c6QAAAAlwSFlzAAALEwAACxMBAJqcGAAAAAd0SU1FB9oMCRUiMrIBQVkAAAAZdEVYdENvbW1lbnQAQ3JlYXRlZCB3aXRoIEdJTVBXgQ4XAAAADElEQVQI12NgoC4AAABQAAEiE+h1AAAAAElFTkSuQmCC";
....
Related
I'm trying to load an image on my HTML5 canvas. I'm following a tutorial and I've done everything precisely.
My console prints "image loaded", so I know that it has found the png file. However, nothing shows up on screen.
I have tried resizing the canvas, and trying to make the image appear on different coordinates, to no avail.
<body>
<canvas id="my_canvas"></canvas>
</body>
<script>
var canvas = null;
var context = null;
var basicImage = null;
var setup = function() {
// Set up canvas
canvas = document.getElementById("my_canvas");
context = canvas.getContext('2d'); // lets us modify canvas visuals later
canvas.width = window.innerWidth; // 1200
canvas.height = window.innerHeight; // 720
// Load an image
basicImage = new Image();
basicImage.src = "bb8.png";
basicImage.onload = onImageLoad();
}
var onImageLoad = function() {
console.log("image loaded");
context.drawImage(basicImage, 0, 0);
}
setup();
</script>
Rather than drawing the image on basicImage.onload, try it on window.onload
var setup = function() {
// Set up canvas
canvas = document.getElementById("my_canvas");
context = canvas.getContext('2d'); // lets us modify canvas visuals later
canvas.width = window.innerWidth; // 1200
canvas.height = window.innerHeight; // 720
// Load an image
basicImage = new Image();
basicImage.src = "bb8.png";
}
window.onload = function() {
console.log("image loaded");
context.drawImage(basicImage, 0, 0);
}
setup();
I am trying to make an image being passed to a canvas from a weburl.
The code has been taken from this [question][1] which is accepted but for some reason it does not work on me on firefox or chrome.
Any ideas?
EDIT:
Here you are:
var myCanvas = document.getElementById('my_canvas_id');
var ctx = myCanvas.getContext('2d');
var img = new Image;
img.onload = function(){
ctx.drawImage(img,0,0); // Or at whatever offset you like
};
img.src = 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAASwAAACWCAYAAABkW7XSAAAAxUlEQVR4nO3BMQEAAADCoPVPbQhfoAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAOA1v9QAATX68/0AAAAASUVORK5CYII=';
The reason nothing shows is that the provided Data-URI contains no data, that is, it is 300x150 fully transparent:
data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAASwAAACWCAYAAABkW7XSAAAAxUlEQVR4nO3BMQEAAADCoPVPbQhfoAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAOA1v9QAATX68/0AAAAASUVORK5CYII=
My guess is that you along the way saved an empty canvas as Data-URI using toDataURL() and is now using that for loading an image.
Try this URL instead and you will see it works (red image of 300x150):
data:image/png;base64,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
var myCanvas = document.getElementById('my_canvas_id');
var ctx = myCanvas.getContext('2d');
var img = new Image;
img.onload = function(){
ctx.drawImage(img,0,0); // Or at whatever offset you like
};
img.src = "data:image/png;base64,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";
<canvas id="my_canvas_id"></canvas>
var ctx=c.getContext("2d");
ctx.fillStyle="red";
ctx.fillRect(0,0,300,150);
document.write(c.toDataURL());
<canvas id="c"></canvas>
I converted an image to canvas and made changes to it and want to convert the canvas with changes to a Data URI and use that for the source of image object or another canvas
I am using the following code to do so but do not get any results. Please suggest any other approach I can use.
Code:
function onPhotoURISuccess(imageURI) {
var largeImage = document.getElementById('testImage'); //image object
var canvas = document.getElementById('canvasPnl');// source canvas
var context= canvas.getContext("2d");
var imageObj = new Image();
imageObj.onload = function(){
context.drawImage(imageObj,0,0,300,300 );
context.fillStyle="#FFFFFF";
context.fillText('Latitude:'+ lat.toString()+'Longitude:'+ lon.toString(),0,10);
context.fillText(new Date(), 0, 20);
context.save();
};
imageObj.src=imageURI;
var img_uri= canvas.toDataURL("image/png");
var image = new Image();
image.src =img_uri;
largeImage.src=img_uri;
var canvas2 = document.getElementById('canvasPnl2');//destination canvas
var context2= canvas2.getContext("2d");
context2.drawImage(image,0,0);
}
You've almost got it.
Since you’re generating a second image object (var image), you must also do a second onload:
var imageObj = new Image();
imageObj.onload = function(){
...
var image = new Image();
image.onload=function(){
...
}
image.src=canvas.toDataURL(); // .png is the default
};
imageObj.crossOrigin="anonymous";
imageObj.src=imageURI;
Also, you have a context.save in there without a context.restore (usually they are paired).
Here is code and a Fiddle: http://jsfiddle.net/m1erickson/ne4Up/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; padding:20px; }
canvas{border:1px solid red;}
img{border:1px solid blue;}
</style>
<script>
$(function(){
var lat="lat";
var lon="long";
onPhotoURISuccess("https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house-icon.png");
function onPhotoURISuccess(imageURI) {
var largeImage = document.getElementById('testImage'); //image object
var canvas = document.getElementById('canvasPnl');// source canvas
var context= canvas.getContext("2d");
var imageObj = new Image();
imageObj.onload = function(){
context.drawImage(imageObj,0,0,100,100 );
context.fillStyle="#FFFFFF";
context.fillText('Latitude:'+ lat.toString()+'Longitude:'+ lon.toString(),0,10);
context.fillText(new Date(), 0, 20);
// context.save(); // where's the matching context.restore();
var image = new Image();
image.onload=function(){
var canvas2 = document.getElementById('canvasPnl2');//destination canvas
var context2= canvas2.getContext("2d");
context2.drawImage(image,0,0);
largeImage.src=canvas2.toDataURL();
}
image.src=canvas.toDataURL(); // .png is the default
};
imageObj.crossOrigin="anonymous";
imageObj.src=imageURI;
}
}); // end $(function(){});
</script>
</head>
<body>
<p>Pnl</p>
<canvas id="canvasPnl" width=100 height=100></canvas>
<p>Pnl2</p>
<canvas id="canvasPnl2" width=100 height=100></canvas>
<p>testImage</p>
<img id=testImage src="houseicon.png" width=100 height=100 >
</body>
</html>
If you simply want to draw a canvas onto another canvas there is no need to convert it to image first. Just use the source canvas directly as an argument to drawImage:
context2.drawImage(canvas, 0, 0);
If you absolutely want to convert it to image first you only need to modify a few lines to handle the asynchronous nature of image loading:
var img_uri= canvas.toDataURL("image/png");
var image = new Image();
var canvas2; /// put them here so they are available outside onload below
var context2;
/// put it in a onload here as well
image.onload = function() {
canvas2 = document.getElementById('canvasPnl2');//destination canvas
context2= canvas2.getContext("2d");
context2.drawImage(image,0,0);
}
image.src =img_uri;
A small note: some versions of Chrome has a bug with new Image. For this reason consider using document.createElement('image') instead.
I am making the simple canvas application.
I want to use image for background of canvas.
I have found out that I should use drawImage(img,x,y).
This is my codes ,but drummap.img doesn't appear.
Where is wrong?
Test
<canvas id="leap-overlay"></canvas>
<script src="leap.js"></script>
<script>
var canvas = document.getElementById("leap-overlay");
// fullscreen
canvas.width = document.body.clientWidth;
canvas.height = document.body.clientHeight;
// create a rendering context
var ctx = canvas.getContext("2d");
ctx.translate(canvas.width/2,canvas.height);
var img = new Image();
img.src = "drummap.jpg";
ctx.drawImage(img,0,0,100,100);
Assuming that your image drummap.jpg is located in said directory, create the image, set the onload to use the new image, and then set the src (see):
var img = new Image();
img.onload = function () {
ctx.drawImage(img, 0, 0, 100, 100);
};
img.src = 'drummap.jpg';
I'm not sure how you're clearing your canvas or what your drawing, but remember your canvas is inherently transparent so feel free to give the canvas a css style background:
<canvas style = "background-image: url(pathtoyourimage.jpg);"></canvas>
Hope that helps.
I'm displaying an image (from a file) on the browser using html... I have another program that keeps taking a screenshot of my screen and storing it as an image file "image.jpeg". I am displaying this image on the browser periodically using setTimeout. However the image is not changing on the browser..
Here is my code... I have used an Image object so that a new image is loaded everytime the javascript function runs, however that does not seem to be working...
<html>
<head>
<script type="text/JavaScript">
var x=0, y=0;
var canvas, context, img;
function timedRefresh(timeoutPeriod)
{
canvas = document.getElementById("x");
context = canvas.getContext("2d");
img = new Image();
img.src = "image.jpeg";
context.drawImage(img, x, y);
x+=20; y+=20;
//img.destroy();
setTimeout("timedRefresh(1000)",timeoutPeriod);
}
</script>
<title>JavaScript Refresh Example</title>
</head>
<body onload="JavaScript:timedRefresh(1000);">
<canvas id="x" width="600" height="600" />
</body>
</html>
First, when you set the src attribute of your image object, the image has not been loaded yet, you need to refresh your canvas when the onload of the image gets fired (when the image is done loading).
Secondly, the browser tries to use the cached image image.jpeg. To avoid that, add a bogus argument to the image URI.
For example :
var timeoutPeriod = 1000;
var imageURI = 'image.jpeg';
var x=0, y=0;
var img = new Image();
img.onload = function() {
var canvas = document.getElementById("x");
var context = canvas.getContext("2d");
context.drawImage(img, x, y);
x+=20; y+=20;
setTimeout(timedRefresh,timeoutPeriod);
};
function timedRefresh() {
// just change src attribute, will always trigger the onload callback
img.src = imageURI + '?d=' + Date.now();
}
And then it should work.
Here a complete working example. Just configure url and refeshInterval. It uses Yannick's caching prevention and does not re-create the img object on every reload as suggested by Piotr.
<html>
<head>
<script type="text/JavaScript">
var url = "cam1.php"; //url to load image from
var refreshInterval = 1000; //in ms
var drawDate = true; //draw date string
var img;
function init() {
var canvas = document.getElementById("canvas");
var context = canvas.getContext("2d");
img = new Image();
img.onload = function() {
canvas.setAttribute("width", img.width)
canvas.setAttribute("height", img.height)
context.drawImage(this, 0, 0);
if(drawDate) {
var now = new Date();
var text = now.toLocaleDateString() + " " + now.toLocaleTimeString();
var maxWidth = 100;
var x = img.width-10-maxWidth;
var y = img.height-10;
context.strokeStyle = 'black';
context.lineWidth = 2;
context.strokeText(text, x, y, maxWidth);
context.fillStyle = 'white';
context.fillText(text, x, y, maxWidth);
}
};
refresh();
}
function refresh()
{
img.src = url + "?t=" + new Date().getTime();
setTimeout("refresh()",refreshInterval);
}
</script>
<title>JavaScript Refresh Example</title>
</head>
<body onload="JavaScript:init();">
<canvas id="canvas"/>
</body>
</html>
I think you don't need to create the Image object every time in timedRefresh(). Just create one instance and constantly change its src attribute. In case of your code snippet, img would have to be global variable.
The main problem, though, is that you will still see flickering (but of different kind) in Opera. See: Image source update in JavaScript with Opera