CODEWITHSUNDEEP
javascripthtmlcanvas
Your choice
Your choice

Reputation: 455

HTML5 canvas drawImage incorrect image size

Hello i have problem i try to drawing image on the canvas with drawImage function 50px x 50px on the 50px x 50px canvas, but i get smaller than i need.

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

var img = new Image();
img.onload = function() {
    $("canvas").css("width", 50);
    $("canvas").css("height", 50);
    ctx.drawImage(img, 0, 0, 50, 50); //bad here why not drawing 50x50px image on the canvas?           
}
img.src = 'http://www.w3schools.com/tags/planets.gif';
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<img src="http://www.w3schools.com/tags/planets.gif" width="100" height="100" style="position: absolute; top: 0px; left: 0px">
<canvas id="canvas" style="position: absolute; top: 0px; left: 120px; border: 1px solid #000"></canvas>

Upvotes: 9

Views: 6922

Answers (1)

Cerbrus
Cerbrus

Reputation: 72857

Don't set a canvas's width and height through CSS. This will stretch / compress the actual canvas, scaling the contents.

Use those old HTML width and height attributes instead:

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

var img = new Image();
img.onload = function() {
    ctx.drawImage(img, 0, 0, 50, 50);
}
img.src = 'http://www.w3schools.com/tags/planets.gif';
<img src="http://www.w3schools.com/tags/planets.gif" width="100" height="100" style="position: absolute; top: 0px; left: 0px">
<canvas
    id="canvas"
    style="position: absolute; top: 0px; left: 120px; border: 1px solid #000"
    width="50"
    height="50">
</canvas>

These attributes actually change the canvas's context's width and height, resulting in a image that's exactly the size you expect it to be.

Upvotes: 20

Related Questions