Canvas wont display image inside of it - javascript

<!DOCTYPE html>
<html>
<head>
<title></title>
</head>
<body>
<canvas id="spriteCanvas" width="500" height="500">
<img id="coin" width="440" height="40" src="coin.png">
</canvas>
</body>
</html>
I tried placing an image inside a canvas element, but it won't display on the browser. I know the image tag works because it's displayed if I place it outside of the canvas element. Also, if I inspect the canvas element, I can see that the image is inside, but its dimensions are 0 by 0. Can somebody explain why this isn't working?
EDIT: My original code added the image through javascript, but it wouldn't show on the canvas. It was giving me the same problems as above. But I just realized I was missing "onload".
original code:
var coinImage = new Image();
coinImage.src = "coin.png";
var sCanvas = document.getElementById('spriteCanvas');
function Sprite(canvas, width, height, image){
this.context = canvas.getContext("2d");
this.width = width;
this.height = height;
this.image = image;
}
Sprite.prototype.render = function() {
var that = this;
this.context.drawImage(that.image, 0, 0);
}
function init() {
var coin = new Sprite(sCanvas, 100, 100, coinImage);
coin.render();
}
init();
editted code:
var coinImage = new Image();
coinImage.src = "coin.png";
var sCanvas = document.getElementById('spriteCanvas');
function Sprite(canvas, width, height, image){
this.context = canvas.getContext("2d");
this.width = width;
this.height = height;
this.image = image;
}
Sprite.prototype.render = function() {
var that = this;
this.context.drawImage(that.image, 0, 0);
}
coinImage.onload = function () {
var coin = new Sprite(sCanvas, 100, 100, coinImage);
coin.render();
}

This isn't how a <canvas> tag works. If you want your image to appear in your canvas, you will have to use JavaScript to place the pixels of the image into your canvas.
<canvas>s are exactly what they state: canvases. They are an element for you to draw on programmatically. If you just want to display an image on a page, you don't need a canvas, you just need the <img> tag. In fact, elements should not be placed in <canvas>.
Take a look at CanvasRenderingContext2D.drawImage() and this tutorial: HTML5 Canvas Image Tutorial.
And this snippet:
var canvas = document.getElementById("painting"),
ctx = canvas.getContext("2d"),
image = new Image();
image.onload = function() {
ctx.drawImage(image, 30, 50);
};
image.src = "http://cdn.sstatic.net/Sites/stackoverflow/img/sprites.png?v=10a9e8743fb0";
<canvas id="painting" width="300" height="300"></canvas>

To draw an image on a canvas, use the following method:
drawImage(image,x,y)
If the image you want to draw is not in the DOM already you can load an image directly from a URL with a few lines of javascript.
function loadAndDrawImage(url)
{
// Create an image object. This is not attached to the DOM and is not part of the page.
var image = new Image();
// When the image has loaded, draw it to the canvas
image.onload = function()
{
// draw image...
}
// Now set the source of the image that we want to load
image.src = url;
}
loadAndDrawImage("http://www---.png");

Related

rendering canvas in firefox not working [duplicate]

I try to build a javascript code, to draw a image on canvas, but I don't know where go wrong.
That is my code:
<body>
<canvas id = "my_canvas"></canvas>
<script>
function setup(){
var canvas = document.getElementById('my_canvas');
var ctx = canvas.getContext('2d');
canvas.width = 800;
canvas.height = 600;
var image = new Image();
image.src = 'a.png';
ctx.drawImage(image,5,5);
};
window.onload = setup;
setup();
</script>
The question is, if I put a line of code setup(); at end then the image is correctly draw, I don't know why.
Thanks.
The problem is that image is loaded asynchronously, so if you set the source and draw it immediately then the image bits are not yet available and nothing is drawn.
You have to wait for the image to load before being able to draw it on a canvas.
Changing the code to
image.onload = function() {
ctx.drawImage(image, 5, 5);
};
image.src = "a.png";
should work as expected.
The image is loading asynchronously. This code will work:
JavaScript:
function setup(){
var canvas = document.getElementById('myCanvas');
var ctx = canvas.getContext('2d');
canvas.width = 800;
canvas.height = 600;
var image = new Image();
image.onload = function () {
ctx.drawImage(image,5,5);
};
image.src = 'a.png';
}
window.onload = setup;

can't add .onclick to image javascript

I want to draw a copy of this image on top of it but further down, but the .onclick isn't working for my image object. I tested it already and it works perfectly fine with canvas.onclick but not with my image 'sticky'.
code is below:
var canvas = document.getElementById('myCanvas');
var context = canvas.getContext("2d");
var sticky = new Image();
sticky.src = "sticky.png";
sticky.onload = function() {
context.drawImage(sticky, 0, 0);
};
sticky.onclick = function() {
context.drawImage(sticky, 0, 100);
};
</script>
Your event needs to be on your canvas, not the image. Because when created, an image object isn't automatically added to the dom.
And when a canvas draw an image, it duplicates it, it copies pixels into itself.
So add your image to the dom, and listen for the click on your canvas.
var canvas = document.getElementById('myCanvas');
var context = canvas.getContext("2d");
var sticky = new Image();
var sticky2 = new Image();
sticky.src = "http://lorempixel.com/250/60/";
sticky2.src = "http://lorempixel.com/150/60/";
sticky.onload = function() {
context.drawImage(sticky, 0, 0);
};
canvas.onclick = function() {
context.drawImage(sticky2, 0, 100);
};
<canvas id="myCanvas"></canvas>

JS to apply to each canvas (multiple)

I want to use StackBlur.js on multiple canvas elements on the same page; however using the example provided by Zurb, I can only apply it to the first canvas element; it ignores the others.
Any idea how to make this code more universal to apply to every canvas element, not just to one?
The JS (by Zurb) is this:
$(function() {
// Change this value to adjust the amount of blur
var BLUR_RADIUS = 100;
var canvas = document.querySelector('[data-canvas]');
var canvasContext = canvas.getContext('2d');
var image = new Image();
image.src = document.querySelector('[data-canvas-image]').src;
var drawBlur = function() {
var w = canvas.width;
var h = canvas.height;
canvasContext.drawImage(image, 0, 0, w, h);
stackBlurCanvasRGBA('heroCanvas', 0, 0, w, h, BLUR_RADIUS);
};
image.onload = function() {
drawBlur();
}
});
The relevant HTML is this:
<canvas class="hero__background" id="heroCanvas" width="200" height="200" data-canvas></canvas>
<!-- Our image to be blurred -->
<img data-canvas-image style="display: none" src="path/to/image.jpg" />
Thank you!
Wrap their code in a loop over all elements with that attribute (in this case data-canvas) like so
$('[data-canvas]').each(function(){
var $el = $(this);
// insert their code here and change it to reference the correct image each time
});
So in the end you can refer to each of the canvases on the page individually, something like so:
$(function(){
// our iteration
$('[data-canvas]').each(function(){
var $el = $(this);
var BLUR_RADIUS = 100;
var canvas = this; // canvas is the element we're iterating over
var canvasContext = canvas.getContext('2d');
var image = new Image();
// I changed the line below of theirs to refer to the canvases attributes
// we're iterating over above
image.src = $el.attr('data-src');
var drawBlur = function() {
var w = canvas.width;
var h = canvas.height;
canvasContext.drawImage(image, 0, 0, w, h);
var id = $el.attr('id'); // use the id from the canvas
stackBlurCanvasRGBA( id, 0, 0, w, h, BLUR_RADIUS);
};
image.onload = function() {
drawBlur();
}
});
});
So now we don't need the images only their src attributes, which now live on the canvases asdata-src`. The the html can be as follows:
<canvas class="hero__background" id="heroCanvas1" data-src="/image/location.jpg" width="200" height="200" data-canvas></canvas>
<canvas class="hero__background" id="heroCanvas2" data-src="/image/location2.jpg" width="200" height="200" data-canvas></canvas>
Update: I realised that you're displaying info in the canvas, and so need more than one. code updated above.
Update 2: I realised that stack blur relies on an id for each call so you need to get that from each canvas in turn, updated code above
Aside: I would recommend iterating over the canvases by class not attribute, but I used it as that was what was in your html. I'd suggest adding a class to each and changing the iteration to something like so:
$('.blurImgCanvas').each(function(){....})

javascript draw a image on canvas

I try to build a javascript code, to draw a image on canvas, but I don't know where go wrong.
That is my code:
<body>
<canvas id = "my_canvas"></canvas>
<script>
function setup(){
var canvas = document.getElementById('my_canvas');
var ctx = canvas.getContext('2d');
canvas.width = 800;
canvas.height = 600;
var image = new Image();
image.src = 'a.png';
ctx.drawImage(image,5,5);
};
window.onload = setup;
setup();
</script>
The question is, if I put a line of code setup(); at end then the image is correctly draw, I don't know why.
Thanks.
The problem is that image is loaded asynchronously, so if you set the source and draw it immediately then the image bits are not yet available and nothing is drawn.
You have to wait for the image to load before being able to draw it on a canvas.
Changing the code to
image.onload = function() {
ctx.drawImage(image, 5, 5);
};
image.src = "a.png";
should work as expected.
The image is loading asynchronously. This code will work:
JavaScript:
function setup(){
var canvas = document.getElementById('myCanvas');
var ctx = canvas.getContext('2d');
canvas.width = 800;
canvas.height = 600;
var image = new Image();
image.onload = function () {
ctx.drawImage(image,5,5);
};
image.src = 'a.png';
}
window.onload = setup;

html5 canvas context .fillStyle not working

Just giving canvas a go for the first time with the intention of creating a game. I have an image displaying but oddly the fillStyle method doesn't seem to be working. ( At least the canvas background is still white in google chrome.)
Note that in my code the canvas var is actually the canvas elements 2d context, maybe that's where i'm getting myself confused? i can't see the problem, would appreciate if anyone else could.
LD24.js:
const FPS = 30;
var canvasWidth = 0;
var canvasHeight = 0;
var xPos = 0;
var yPos = 0;
var smiley = new Image();
smiley.src = "http://javascript-tutorials.googlecode.com/files/jsplatformer1-smiley.jpg";
var canvas = null;
window.onload = init; //set init function to be called onload
function init(){
canvasWidth = document.getElementById('canvas').width;
canvasHeight = document.getElementById('canvas').height;
canvas = document.getElementById('canvas').getContext('2d');
setInterval(function(){
update();
draw();
}, 1000/FPS);
}
function update(){
}
function draw()
{
canvas.clearRect(0,0,canvasWidth,canvasHeight);
canvas.fillStyle = "#FFAA33"; //orange fill
canvas.drawImage(smiley, xPos, yPos);
}
LD24.html:
<html>
<head>
<script language="javascript" type="text/javascript" src="LD24.js"></script>
</head>
<body>
<canvas id="canvas" width="800" height="600">
<p> Your browser does not support the canvas element needed to play this game :(</p>
</canvas>
</body>
</html>
3 notes:
fillStyle does not cause your canvas to be filled. It means that when you fill a shape it will be filled with that color. Therefore you need to write canvas.fillRect( xPos, yPos, width, height).
Wait until your image actually loads, otherwise the rendering may be inconsistent or buggy.
Careful of cross-domain images used in your canvas - most browsers will throw a security exception and stop executing your code.
Wait till image loads as well:
var img = new Image();
img.onload = function() {
handleLoadedTexture(img);
};
img.src = "image.png";
function handleLoadedTexture(img) {
//call loop etc that uses image
};
Or maybe you were just missing
canvas.fill();
after
canvas.drawImage(smiley, xPos, yPos);

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