CanvasRenderingContext2D.clearRect()

The CanvasRenderingContext2D.clearRect() 是 Canvas 2D API 设置指定矩形区域内（以 点 (x, y) 为起点，范围是(width, height) ）所有像素变成透明，并擦除之前绘制的所有内容的方法。

语法

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

参数

x
矩形起点的 x 轴坐标。
y
矩形起点的 y 轴坐标。
width
矩形的宽度。
height
矩形的高度。

示例

使用 clearRect 方法

这仅是一段简单地使用 clearRect 方法的代码片段。

HTML

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

JavaScript

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

ctx.beginPath();
ctx.moveTo(20,20);
ctx.lineTo(200,20);
ctx.lineTo(120,120);
ctx.closePath(); // draws last line of the triangle
ctx.stroke();

ctx.clearRect(10, 10, 100, 100);

// clear the whole canvas
// ctx.clearRect(0, 0, canvas.width, canvas.height);

你可以修改下面的代码, 在此处在线查看代码效果:

Playable code
<canvas id="canvas" width="400" height="200" class="playable-canvas"></canvas>
<div class="playable-buttons">
  <input id="edit" type="button" value="Edit" />
  <input id="reset" type="button" value="Reset" />
</div>
<textarea id="code" class="playable-code" style="height:140px;">
ctx.beginPath();
ctx.moveTo(20,20);
ctx.lineTo(200,20);
ctx.lineTo(120,120);
ctx.closePath(); // draws last line of the triangle
ctx.stroke();

ctx.clearRect(10, 10, 100, 100);</textarea>

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var textarea = document.getElementById("code");
var reset = document.getElementById("reset");
var edit = document.getElementById("edit");
var code = textarea.value;

function drawCanvas() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  eval(textarea.value);
}

reset.addEventListener("click", function() {
  textarea.value = code;
  drawCanvas();
});

edit.addEventListener("click", function() {
  textarea.focus();
})

textarea.addEventListener("input", drawCanvas);
window.addEventListener("load", drawCanvas);

规范描述

Specification Status Comment
HTML Living Standard
CanvasRenderingContext2D.clearRect		 Living Standard  

浏览器兼容性

We're converting our compatibility data into a machine-readable JSON format. This compatibility table still uses the old format, because we haven't yet converted the data it contains. Find out how you can help!

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support (Yes) (Yes) (Yes) (Yes) (Yes)
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

参见

相关主题
  1. CanvasRenderingContext2D
  2. 属性
    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. isPointInPath()
    25. isPointInStroke()
    26. lineTo()
    27. measureText()
    28. moveTo()
    29. putImageData()
    30. quadraticCurveTo()
    31. rect()
    32. removeHitRegion()
    33. resetTransform()
    34. restore()
    35. rotate()
    36. save()
    37. scale()
    38. scrollPathIntoView()
    39. setLineDash()
    40. setTransform()
    41. stroke()
    42. strokeRect()
    43. strokeText()
    44. transform()
    45. translate()