Recently, I suddenly wanted to study the function of rotating images in js. I won’t talk about the previous implementation methods first. HTML5 is very good now. Let’s mainly understand the image rotation in HTML5.
Example demonstration:
http://www.imqing.com/demo/rotateImg.html
Principle: Use canvas object to rotate.
Implementation method: First create a canvas element, and then draw the img element into the canvas. However, in fact, this is the default situation, when the image is not rotated. If the picture needs to be rotated 90 degrees, you need to rotate the canvas 90 degrees before drawing.
The description is as follows:
The internal rotation principle is like this. The coordinates of the picture are calculated from the upper left corner. To the right is the positive x direction, and down is the positive y direction. When rotating the canvas When, the coordinates are actually rotating, so the final drawing method is different.
At that time, I also used picpick to measure the coordinates of the starting point after rotating a certain angle, and then I realized that the original rotation was like this.
Code:
<body>
<button onclick="rotateImg('testImg', 'left')">向左旋转</button>
<button onclick="rotateImg('testImg', 'right')">向右旋转</button><br/>
<img src="/static/imghwm/default1.png" data-src="./test.jpg" class="lazy" id="testImg"/ alt="How to rotate images using HTML5 canvas? (Example demonstration)" >
<script>
function rotateImg(pid, direction) {
//最小与最大旋转方向，图片旋转4次后回到原方向
var min_step = 0;
var max_step = 3;
var img = document.getElementById(pid);
if (img == null)return;
//img的高度和宽度不能在img元素隐藏后获取，否则会出错
var height = img.height;
var width = img.width;
var step = img.getAttribute('step');
if (step == null) {
step = min_step;
}
if (direction == 'right') {
step++;
//旋转到原位置，即超过最大值
step > max_step && (step = min_step);
} else {
step--;
step < min_step && (step = max_step);
}
img.setAttribute('step', step);
var canvas = document.getElementById('pic_' + pid);
if (canvas == null) {
img.style.display = 'none';
canvas = document.createElement('canvas');
canvas.setAttribute('id', 'pic_' + pid);
img.parentNode.appendChild(canvas);
}
//旋转角度以弧度值为参数
var degree = step * 90 * Math.PI / 180;
var ctx = canvas.getContext('2d');
switch (step) {
case 0:
canvas.width = width;
canvas.height = height;
ctx.drawImage(img, 0, 0);
break;
case 1:
canvas.width = height;
canvas.height = width;
ctx.rotate(degree);
ctx.drawImage(img, 0, -height);
break;
case 2:
canvas.width = width;
canvas.height = height;
ctx.rotate(degree);
ctx.drawImage(img, -width, -height);
break;
case 3:
canvas.width = height;
canvas.height = width;
ctx.rotate(degree);
ctx.drawImage(img, -width, 0);
break;
}
}
</script>
</body>Explanation: There is no need to explain canvas.width and height, it should be. You shouldn’t need to rotate, right? The key is drawImage(img, x, y);
x and y refer to the point from which to start drawing. Because the entire coordinate system is rotated, x and y are different. , for example step=1, the picture is rotated 90 degrees to the right, that is, the coordinate system is rotated 90 degrees, then the starting position should be x = 0, y= img.height
The above is the detailed content of How to rotate images using HTML5 canvas? (Example demonstration). For more information, please follow other related articles on the PHP Chinese website!
The Future of HTML, CSS, and JavaScript: Web Development TrendsApr 19, 2025 am 12:02 AMThe future trends of HTML are semantics and web components, the future trends of CSS are CSS-in-JS and CSSHoudini, and the future trends of JavaScript are WebAssembly and Serverless. 1. HTML semantics improve accessibility and SEO effects, and Web components improve development efficiency, but attention should be paid to browser compatibility. 2. CSS-in-JS enhances style management flexibility but may increase file size. CSSHoudini allows direct operation of CSS rendering. 3.WebAssembly optimizes browser application performance but has a steep learning curve, and Serverless simplifies development but requires optimization of cold start problems.
HTML: The Structure, CSS: The Style, JavaScript: The BehaviorApr 18, 2025 am 12:09 AMThe roles of HTML, CSS and JavaScript in web development are: 1. HTML defines the web page structure, 2. CSS controls the web page style, and 3. JavaScript adds dynamic behavior. Together, they build the framework, aesthetics and interactivity of modern websites.
The Future of HTML: Evolution and Trends in Web DesignApr 17, 2025 am 12:12 AMThe future of HTML is full of infinite possibilities. 1) New features and standards will include more semantic tags and the popularity of WebComponents. 2) The web design trend will continue to develop towards responsive and accessible design. 3) Performance optimization will improve the user experience through responsive image loading and lazy loading technologies.
HTML vs. CSS vs. JavaScript: A Comparative OverviewApr 16, 2025 am 12:04 AMThe roles of HTML, CSS and JavaScript in web development are: HTML is responsible for content structure, CSS is responsible for style, and JavaScript is responsible for dynamic behavior. 1. HTML defines the web page structure and content through tags to ensure semantics. 2. CSS controls the web page style through selectors and attributes to make it beautiful and easy to read. 3. JavaScript controls web page behavior through scripts to achieve dynamic and interactive functions.
HTML: Is It a Programming Language or Something Else?Apr 15, 2025 am 12:13 AMHTMLisnotaprogramminglanguage;itisamarkuplanguage.1)HTMLstructuresandformatswebcontentusingtags.2)ItworkswithCSSforstylingandJavaScriptforinteractivity,enhancingwebdevelopment.
HTML: Building the Structure of Web PagesApr 14, 2025 am 12:14 AMHTML is the cornerstone of building web page structure. 1. HTML defines the content structure and semantics, and uses, etc. tags. 2. Provide semantic markers, such as, etc., to improve SEO effect. 3. To realize user interaction through tags, pay attention to form verification. 4. Use advanced elements such as, combined with JavaScript to achieve dynamic effects. 5. Common errors include unclosed labels and unquoted attribute values, and verification tools are required. 6. Optimization strategies include reducing HTTP requests, compressing HTML, using semantic tags, etc.
From Text to Websites: The Power of HTMLApr 13, 2025 am 12:07 AMHTML is a language used to build web pages, defining web page structure and content through tags and attributes. 1) HTML organizes document structure through tags, such as,. 2) The browser parses HTML to build the DOM and renders the web page. 3) New features of HTML5, such as, enhance multimedia functions. 4) Common errors include unclosed labels and unquoted attribute values. 5) Optimization suggestions include using semantic tags and reducing file size.
Understanding HTML, CSS, and JavaScript: A Beginner's GuideApr 12, 2025 am 12:02 AMWebdevelopmentreliesonHTML,CSS,andJavaScript:1)HTMLstructurescontent,2)CSSstylesit,and3)JavaScriptaddsinteractivity,formingthebasisofmodernwebexperiences.
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
MinGW - Minimalist GNU for Windows
This project is in the process of being migrated to osdn.net/projects/mingw, you can continue to follow us there. MinGW: A native Windows port of the GNU Compiler Collection (GCC), freely distributable import libraries and header files for building native Windows applications; includes extensions to the MSVC runtime to support C99 functionality. All MinGW software can run on 64-bit Windows platforms.
SublimeText3 English version
Recommended: Win version, supports code prompts!
SublimeText3 Chinese version
Chinese version, very easy to use
VSCode Windows 64-bit Download
A free and powerful IDE editor launched by Microsoft
DVWA
Damn Vulnerable Web App (DVWA) is a PHP/MySQL web application that is very vulnerable. Its main goals are to be an aid for security professionals to test their skills and tools in a legal environment, to help web developers better understand the process of securing web applications, and to help teachers/students teach/learn in a classroom environment Web application security. The goal of DVWA is to practice some of the most common web vulnerabilities through a simple and straightforward interface, with varying degrees of difficulty. Please note that this software
