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• 句法
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

CanvasRenderingContext2D .clearRect() method of the Canvas 2D API erases the pixels in a rectangular area by setting them to transparent black.

注意： 要意识到， clearRect() may cause unintended side effects if you're not using paths properly . Make sure to call beginPath() before starting to draw new items after calling clearRect() .

句法

void ctx.clearRect(x, y, width, height);
					

clearRect() method sets the pixels in a rectangular area to transparent black ( rgba(0,0,0,0) ). The rectangle's corner is at (x, y) , and its size is specified by width and height .

参数

x

The x-axis coordinate of the rectangle's starting point.

y

The y-axis coordinate of the rectangle's starting point.

width

The rectangle's width. Positive values are to the right, and negative to the left.

height

The rectangle's height. Positive values are down, and negative are up.

范例

Erasing the whole canvas

This code snippet erases the entire canvas. This is commonly required at the start of each frame in an animation. The dimensions of the cleared area are set to equal the <canvas> 元素的 width and height 属性。

const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');
ctx.clearRect(0, 0, canvas.width, canvas.height);
					

Erasing part of a canvas

This example draws a blue triangle on top of a yellowish background. The clearRect() method then erases part of the canvas.

HTML

<canvas id="canvas"></canvas>
					

JavaScript

The cleared area is rectangular in shape, with its top-left corner at (10, 10). The cleared area has a width of 120 and a height of 100.

const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');
// Draw yellow background
ctx.beginPath();
ctx.fillStyle = '#ff6';
ctx.fillRect(0, 0, canvas.width, canvas.height);
// Draw blue triangle
ctx.beginPath();
ctx.fillStyle = 'blue';
ctx.moveTo(20, 20);
ctx.lineTo(180, 20);
ctx.lineTo(130, 130);
ctx.closePath();
ctx.fill();
// Clear part of the canvas
ctx.clearRect(10, 10, 120, 100);
					

结果

规范

规范	状态	注释
HTML 实时标准 The definition of 'CanvasRenderingContext2D.clearRect' in that specification.	实时标准

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	桌面						移动
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
clearRect	Chrome Yes	Edge 12	Firefox 1.5	IE Yes	Opera Yes	Safari Yes	WebView Android Yes	Chrome Android Yes	Firefox Android 4	Opera Android Yes	Safari iOS Yes	Samsung Internet Android Yes

图例

完整支持

完整支持

另请参阅

• The interface defining this method: CanvasRenderingContext2D
• CanvasRenderingContext2D.fillRect()
• CanvasRenderingContext2D.strokeRect()

元数据

• 最后修改： 2019 年 3 月 23 日

相关话题

1. CanvasRenderingContext2D
2. 特性

   1. canvas
   2. currentTransform
   3. direction
   4. fillStyle
   5. filter
   6. font
   7. globalAlpha
   8. globalCompositeOperation
   9. imageSmoothingEnabled
   10. imageSmoothingQuality
   11. lineCap
   12. lineDashOffset
   13. lineJoin
   14. lineWidth
   15. miterLimit
   16. shadowBlur
   17. shadowColor
   18. shadowOffsetX
   19. shadowOffsetY
   20. strokeStyle
   21. textAlign
   22. textBaseline
3. 方法

   1. addHitRegion()
   2. arc()
   3. arcTo()
   4. beginPath()
   5. bezierCurveTo()
   6. clearHitRegions()
   7. clearRect()
   8. clip()
   9. closePath()
   10. createImageData()
   11. createLinearGradient()
   12. createPattern()
   13. createRadialGradient()
   14. drawFocusIfNeeded()
   15. drawImage()
   16. drawWidgetAsOnScreen()
   17. drawWindow()
   18. ellipse()
   19. fill()
   20. fillRect()
   21. fillText()
   22. getImageData()
   23. getLineDash()
   24. getTransform()
   25. isPointInPath()
   26. isPointInStroke()
   27. lineTo()
   28. measureText()
   29. moveTo()
   30. putImageData()
   31. quadraticCurveTo()
   32. rect()
   33. removeHitRegion()
   34. resetTransform()
   35. restore()
   36. rotate()
   37. save()
   38. scale()
   39. scrollPathIntoView()
   40. setLineDash()
   41. setTransform()
   42. stroke()
   43. strokeRect()
   44. strokeText()
   45. transform()
   46. translate()