Canvas 2D API 的 CanvasRenderingContext2D.clearRect() 方法可以設定指定矩形（經由坐標 (x, y) 及大小 (width, height)）範圍內的所有像素為透明，清除所有先前繪製的內容。
void ctx.clearRect(x, y, width, height);
xywidthheightA common problem with clearRect is that it may appear it does not work when not using paths properly. Don't forget to call {{domxref("CanvasRenderingContext2D.beginPath", "beginPath()")}} before starting to draw the new frame after calling clearRect.
clearRect methodThis is just a simple code snippet which uses the clearRect method.
<canvas id="canvas"></canvas>
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:
<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);
{{ EmbedLiveSample('Playable_code', 700, 400) }}
| Specification | Status | Comment |
|---|---|---|
| {{SpecName('HTML WHATWG', "scripting.html#dom-context-2d-clearrect", "CanvasRenderingContext2D.clearRect")}} | {{Spec2('HTML WHATWG')}} |