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    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);

    Edit the code below and see your changes update live in the canvas:

    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
    WHATWG HTML Living Standard
    CanvasRenderingContext2D.clearRect    		 Living Standard  

    浏览器兼容性

    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

    文档标签和贡献者

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