HTML的元素通過JavaScript用於在網頁上渲染圖形，其本身不具備顯示形狀或圖像的能力，必須通過腳本繪製。 1. 它支持繪製基本形狀如矩形、圓形和線條，常用方法包括fillRect()填充矩形、strokeRect()描邊矩形和clearRect()清除區(qū)域；2. 可以渲染圖像和文本，使用drawImage()放置圖像，fillText()繪製文本；3. 適合動畫和實時圖形，通過反復清除和重繪實現動畫效果，並可結合requestAnimationFrame()優(yōu)化性能；4. 缺點是內容不可訪問，不適合需要SEO或屏幕閱讀器支持的場景，但對於高性能視覺交互，它是HTML中功能強大的工具。

The HTML <canvas></canvas> element is used for rendering graphics on a web page using JavaScript. Unlike other HTML elements, it doesn't have built-in capabilities to display shapes or images by itself — you need to use scripting (usually JavaScript) to draw and manipulate visuals directly on the canvas surface.

Drawing Basic Shapes

With the canvas API, you can draw rectangles, circles, lines, and more. It's commonly used for games, animations, or visualizations where dynamic rendering is needed. For example:

• fillRect() draws a filled rectangle
• strokeRect() outlines a rectangle without filling it
• clearRect() clears a rectangular area

To start drawing, you first get the canvas context with something like ctx = canvas.getContext('2d') , then call drawing methods on that context.

Rendering Images and Text

Canvas isn't limited to just shapes — you can also draw images and text. The drawImage() method allows placing images (even from external sources) onto the canvas. Similarly, fillText() lets you render text dynamically, useful for data visualizations or game UIs.

One thing to note: once something is drawn, the canvas doesn't keep track of it. If you want to update part of the scene, you usually redraw the entire canvas or manage layers manually.

Animation and Real-Time Graphics

Because canvas gives you direct pixel control, it's great for animation. You can clear and redraw frames repeatedly, creating smooth motion effects. This makes it popular in browser-based games and interactive data dashboards.

A typical animation loop uses requestAnimationFrame() to efficiently update visuals. You might also combine canvas with libraries like p5.js or Three.js for more advanced effects without writing everything from scratch.

Keep in mind that canvas content isn't accessible like regular DOM elements. So if you're building something that needs screen reader support or SEO-friendly content, canvas may not be the best fit.

But for visual interactivity that runs fast and offers fine control, the canvas element is one of the most powerful tools in HTML.

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