Code Snippet </> Info
Snippet Name: Resize an Image Using Canvas, Drag and Drop and the File API
Description: A user interface that allows a user to upload an image that is automagically re-sized to your specifications before uploading to a server. Example: View Code Demo
Note: Set your var MAX_HEIGHT = 100; Add it to your form.
Author: David Walsh
Last Modified: 2019-12-09 02:53:10
Language: javascript
Highlight Mode: javascript
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<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" dir="ltr">
<head>
<title>Resize an Image Using Canvas, Drag and Drop and the File API</title>
<meta name="description" content="Use the File API, drag and drop, and HTML5 canvas to allow for JavaScript resizing of images." />
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<!--[if lt IE 9]>
<script src="http://html5shiv.googlecode.com/svn/trunk/html5.js"></script>
<![endif]-->
<style>
/* Begin Resize an Image Using Canvas, Drag and Drop and the File API */
/* == This Script Free To Use Providing This Notice Remains == */
/* == This Script Has Been Found In The https://snapbuilder.com Free Public Codes Library == */
/* == NOTICE:Though This Material May Have Been In A Public Depository, Certain Author Copyright Restrictions May Apply == */
/* == Created by: David Walsh : http://davidwalsh.name/demo/resize-image-canvas.php : Creative Commons License == */
BODY {font-family:verdana,arial,ms sans serif; font-size:90%; background-color:#ffffff; color:#000000;}
#content {margin:0px 15px 0px 15px; padding:15px 15px 15px 15px;}
#preview-row {
position:relative;
width:auto;
padding:12px;
border:1px solid #ddd;
}
#drop-target {
position:absolute;
top:12px;
left:12px;
width:100px;
height:100px;
background-color:#eee;
border:1px solid #ddd;
text-align:center;
padding:12px;
}
#preview {
width:auto;
margin-left:148px;
height:100px;
background-color:#eee;
padding:12px;
border:1px solid #ddd;
}</style>
<script src="http://ajax.googleapis.com/ajax/libs/dojo/1.9.1/dojo/dojo.js"></script>
</head>
<body>
<div id="content">
<h1>Resize an Image Using Canvas, Drag and Drop and the File API</h1>
<div class="p">Read <a href="http://davidwalsh.name/resize-image-canvas" target="_new">Resize an Image Using Canvas, Drag and Drop and the File API</a></div>
<div id="promoNode"></div>
<p>Drag an image into the box below to see it automagically resized with canvas and JavaScript.</p>
<div id="preview-row">
<div id="drop-target">Drop your image file in to this box.</div>
<div id="preview">
<canvas id="canvas"></canvas>
</div>
</div>
<script>
require(["dojo/dom", "dojo/domReady!"], function(dom){
var MAX_HEIGHT = 100; /* set your max image height */
var target = dom.byId("drop-target"),
preview = dom.byId("preview"),
canvas = dom.byId("canvas");
var render = function(src){
var img = new Image();
img.onload = function(){
if(img.height > MAX_HEIGHT) {
img.width *= MAX_HEIGHT / img.height;
img.height = MAX_HEIGHT;
}
var ctx = canvas.getContext("2d");
ctx.clearRect(0, 0, canvas.width, canvas.height);
preview.style.width = img.width + "px";
preview.style.height = img.height + "px";
canvas.width = img.width;
canvas.height = img.height;
ctx.drawImage(img, 0, 0, img.width, img.height);
};
img.src = src;
};
var readImage = function(imgFile){
if(!imgFile.type.match(/image.*/)){
console.log("Sorry, the dropped file is not an image:", imgFile.type);
return;
}
var reader = new FileReader();
reader.onload = function(e){
render(e.target.result);
};
reader.readAsDataURL(imgFile);
};
// DOMReady setup
target.addEventListener("dragover", function(e) {e.preventDefault();}, true);
target.addEventListener("drop", function(e){
e.preventDefault();
readImage(e.dataTransfer.files[0]);
}, true);
});
</script>
</div>
</body>
</html>
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