Having trouble with JavaScript canvas drawImage function not functioning correctly

Having some trouble drawing part of an image properly. The width and height are not matching the original.

Check out my code below:

window.onload = function() {
ImageObjSketch = new Image(); // URL
ImageObjSketch.src = 'https://i.imgur.com/75lATF9.png';

canvasClone = document.getElementById("squareTarget");
ctxClone = canvasClone.getContext("2d");
ctxClone.drawImage(ImageObjSketch,34,119,16,16,0,0,38,38);
}
#squareTarget {
width: 38px; height: 38px;
position: relative;
right: 0px;
display: inline-block;
border: 1px #000000 solid;
}
<canvas id="squareTarget"></canvas>

The square size is not proportional to the image, even though I specified a full size.

Also, why does this code need to be run twice in order to see the image?

javascripthtml5-canvasdrawimage

Answer №1

If you want to create a canvas, it's important to define its size explicitly before accessing the 2D Context:

window.onload = function() {
var ImageObjSketch = new Image(); // URL
ImageObjSketch.src = 'https://i.imgur.com/75lATF9.png';

var canvasClone = document.getElementById("squareTarget");
canvasClone.width = 38;
canvasClone.height = 38;
ctxClone = canvasClone.getContext("2d");


ctxClone.drawImage(ImageObjSketch, 34,119,16,16,0,0,38,38);
}

Instead of hardcoding the size as 38, consider using the document's height and width for better flexibility:

ctxClone.drawImage(ImageObjSketch, 34,119,16,16,0,0,canvasClone.width,canvasClone.height);

Check out this CodePen link for a live demonstration.

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