Web Front-end
H5 Tutorial
How to solve cross-domain problems encountered when drawing on canvas
How to solve cross-domain problems encountered when drawing on canvas
This article mainly introduces relevant information that explains in detail the cross-domain problems encountered when drawing canvas. The content is quite good. I will share it with you now and give it as a reference.
When drawing an external link image in canvas, we will encounter a cross-domain problem.
The example is as follows:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>crossorigin</title>
</head>
<body>
<canvas width="600" height="300" id="canvas"></canvas>
<img id="image" alt="">
<script>
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var image = new Image();
image.onload = function() {
ctx.drawImage(image, 0, 0);
document.getElementById('image').src = canvas.toDataURL('image/png');
};
image.src = 'https://ss0.bdstatic.com/70cFvHSh_Q1YnxGkpoWK1HF6hhy/it/u=3497300994,2503543630&fm=27&gp=0.jpg';
</script>
</body>When you open this page in the browser, you will find this problem:
Uncaught DOMException: Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported.
This is limited by the CORS policy and there will be cross-domain problems, although it can be used Image, but drawing it to the canvas will pollute the canvas. Once a canvas is polluted, the data of the canvas cannot be extracted. For example, the canvas toBlob(), toDataURL(), or getImageData() methods cannot be used; when using these methods, it will The above security error is thrown
This is a distressing problem, but fortunately img has added the crossorigin attribute. This attribute determines whether the CORS function is enabled during the image acquisition process:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>crossorigin</title>
</head>
<body>
<canvas width="600" height="300" id="canvas"></canvas>
<img id="image" alt="">
<script>
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var image = new Image();
image.setAttribute('crossorigin', 'anonymous');
image.onload = function() {
ctx.drawImage(image, 0, 0);
document.getElementById('image').src = canvas.toDataURL('image/png');
};
image.src = 'https://ss0.bdstatic.com/70cFvHSh_Q1YnxGkpoWK1HF6hhy/it/u=3497300994,2503543630&fm=27&gp=0.jpg';
</script>
</body>Comparing the above two pieces of JS code, you will find this extra line:
image.setAttribute('crossorigin', 'anonymous');
It’s that simple, Perfect solution!
The above is the entire content of this article. I hope it will be helpful to everyone’s study. For more related content, please pay attention to the PHP Chinese website!
Related recommendations:
About the properties of canvas lines
##How to use canvas to achieve image mosaic
The above is the detailed content of How to solve cross-domain problems encountered when drawing on canvas. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
Which schools use canvas?
Aug 18, 2023 pm 05:59 PM
Schools using canvas include Stanford University, MIT, Columbia University, University of California, Berkeley, etc. Detailed introduction: 1. Stanford University uses Canvas as its main online learning platform. Teachers and students at Stanford University use Canvas to manage and communicate course content, and learn through functions such as online discussions, assignment submissions, and exams; 2. Ma Provincial Polytechnic Institute and MIT also use Canvas as their online learning management system and conduct course management through the Canvas platform; 3. Columbia University, etc.
What are the canvas arrow plug-ins?
Aug 21, 2023 pm 02:14 PM
The canvas arrow plug-ins include: 1. Fabric.js, which has a simple and easy-to-use API and can create custom arrow effects; 2. Konva.js, which provides the function of drawing arrows and can create various arrow styles; 3. Pixi.js , which provides rich graphics processing functions and can achieve various arrow effects; 4. Two.js, which can easily create and control arrow styles and animations; 5. Arrow.js, which can create various arrow effects; 6. Rough .js, you can create hand-drawn arrows, etc.
Learn the canvas framework and explain the commonly used canvas framework in detail
Jan 17, 2024 am 11:03 AM
Explore the Canvas framework: To understand what are the commonly used Canvas frameworks, specific code examples are required. Introduction: Canvas is a drawing API provided in HTML5, through which we can achieve rich graphics and animation effects. In order to improve the efficiency and convenience of drawing, many developers have developed different Canvas frameworks. This article will introduce some commonly used Canvas frameworks and provide specific code examples to help readers gain a deeper understanding of how to use these frameworks. 1. EaselJS framework Ea
What are the details of the canvas clock?
Aug 21, 2023 pm 05:07 PM
The details of the canvas clock include clock appearance, tick marks, digital clock, hour, minute and second hands, center point, animation effects, other styles, etc. Detailed introduction: 1. Clock appearance, you can use Canvas to draw a circular dial as the appearance of the clock, and you can set the size, color, border and other styles of the dial; 2. Scale lines, draw scale lines on the dial to represent hours or minutes. Position; 3. Digital clock, you can draw a digital clock on the dial to indicate the current hour and minute; 4. Hour hand, minute hand, second hand, etc.
What versions of html2canvas are there?
Aug 22, 2023 pm 05:58 PM
The versions of html2canvas include html2canvas v0.x, html2canvas v1.x, etc. Detailed introduction: 1. html2canvas v0.x, which is an early version of html2canvas. The latest stable version is v0.5.0-alpha1. It is a mature version that has been widely used and verified in many projects; 2. html2canvas v1.x, this is a new version of html2canvas.
uniapp implements how to use canvas to draw charts and animation effects
Oct 18, 2023 am 10:42 AM
How to use canvas to draw charts and animation effects in uniapp requires specific code examples 1. Introduction With the popularity of mobile devices, more and more applications need to display various charts and animation effects on the mobile terminal. As a cross-platform development framework based on Vue.js, uniapp provides the ability to use canvas to draw charts and animation effects. This article will introduce how uniapp uses canvas to achieve chart and animation effects, and give specific code examples. 2. canvas
What properties does tkinter canvas have?
Aug 21, 2023 pm 05:46 PM
The tkinter canvas attributes include bg, bd, relief, width, height, cursor, highlightbackground, highlightcolor, highlightthickness, insertbackground, insertwidth, selectbackground, selectforeground, xscrollcommand attributes, etc. Detailed introduction
Where are the canvas mouse coordinates?
Aug 22, 2023 pm 03:08 PM
How to get mouse coordinates for canvas: 1. Create a JavaScript sample file; 2. Get a reference to the Canvas element and add a listener for mouse movement events; 3. When the mouse moves on the Canvas, the getMousePos function will be triggered; 4. Use The "getBoundingClientRect()" method obtains the position and size information of the Canvas element, and obtains the mouse coordinates through event.clientX and event.clientY.
