HTML5的元素是一個(gè)空白繪圖區(qū)域，通過(guò)JavaScript可創(chuàng)建圖形、動(dòng)畫或可視化內(nèi)容。 1. 首先在HTML中添加標(biāo)籤並設(shè)置寬高；2. 使用JavaScript通過(guò)getElementById獲取canvas對(duì)象，並調(diào)用getContext('2d')獲取2D繪圖上下文；3. 利用fillRect、strokeRect等方法繪製形狀；4. 通過(guò)font、fillText等方法添加文本，通過(guò)Image對(duì)象和drawImage方法加載並繪製圖像，注意使用onload確保圖像加載完成；5. 添加事件監(jiān)聽器如click、mousemove等實(shí)現(xiàn)用戶交互，獲取點(diǎn)擊或移動(dòng)坐標(biāo)以實(shí)現(xiàn)互動(dòng)效果。 Canvas本身不自帶交互邏輯，所有功能需自行實(shí)現(xiàn)。

The HTML5 <canvas></canvas> element is a blank drawing area you can manipulate with JavaScript to create graphics, animations, or visual content directly in the browser. It doesn't do much on its own — think of it like a digital whiteboard — but once you add JavaScript, you can draw shapes, text, images, and even create interactive visuals.

How to Set Up a Basic Canvas

To use the <canvas></canvas> element, you first need to add it to your HTML file. Here's a simple example:

 <canvas id="myCanvas" width="500" height="300"></canvas>

This creates a canvas area 500 pixels wide and 300 pixels tall. By itself, it won't show anything unless you use JavaScript to draw on it.

To start drawing, you'll need to access the canvas through JavaScript:

 const canvas = document.getElementById('myCanvas');
const ctx = canvas.getContext('2d');

The getContext('2d') gives you a 2D drawing context, which is the most commonly used one for basic graphics.

Drawing Simple Shapes

Once you have the canvas context, you can begin drawing. For example, drawing a rectangle is straightforward:

• Use ctx.fillStyle = 'red'; to set the fill color.
• Then call ctx.fillRect(x, y, width, height); to draw the rectangle.

Here's a full example:

 ctx.fillStyle = 'blue';
ctx.fillRect(50, 50, 100, 100);

This draws a blue square starting at coordinates (50, 50), 100 pixels wide and tall.

You can also draw outlines using ctx.strokeRect() or even clear parts of the canvas with ctx.clearRect() .

Adding Text and Images

Text and images make canvas content more dynamic. To add text:

 ctx.font = '20px Arial';
ctx.fillStyle = 'black';
ctx.fillText('Hello Canvas!', 10, 50);

This displays the text "Hello Canvas!" at position (10, 50) using a 20px Arial font.

For images, you can load an image from a URL and draw it onto the canvas:

 const img = new Image();
img.src = 'image.png';
img.onload = () => {
  ctx.drawImage(img, 0, 0);
};

This loads an image and draws it at the top-left corner of the canvas once it's ready.

Just keep in mind: if the image isn't fully loaded before drawImage() runs, it won't appear. That's why we use the onload event.

Handling User Interaction

One powerful feature of the canvas is that it can respond to user input like clicks or mouse movement.

For example, to detect a click on the canvas:

 canvas.addEventListener('click', function(event) {
  const rect = canvas.getBoundingClientRect();
  const x = event.clientX - rect.left;
  const y = event.clientY - rect.top;
  console.log('Clicked at:', x, y);
});

This gives you the exact coordinates of the click, which you can then use to determine if the user clicked on a specific shape or area.

You can also track mouse movement with mousemove or handle touch events on mobile devices using touchstart and similar events.

基本上就這些。 Canvas 提供了很靈活的繪圖能力，但所有交互和logic 都需要你自己用JS 來(lái)實(shí)現(xiàn)。

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