From 218934fa2ed1c702a6d3923d2aa2cc6b43c48684 Mon Sep 17 00:00:00 2001 From: Peter Bengtsson Date: Tue, 8 Dec 2020 14:43:23 -0500 Subject: initial commit --- .../canvasrenderingcontext2d/clearrect/index.html | 189 +++++++++++++++++++++ 1 file changed, 189 insertions(+) create mode 100644 files/zh-tw/web/api/canvasrenderingcontext2d/clearrect/index.html (limited to 'files/zh-tw/web/api/canvasrenderingcontext2d/clearrect') diff --git a/files/zh-tw/web/api/canvasrenderingcontext2d/clearrect/index.html b/files/zh-tw/web/api/canvasrenderingcontext2d/clearrect/index.html new file mode 100644 index 0000000000..e5792ffade --- /dev/null +++ b/files/zh-tw/web/api/canvasrenderingcontext2d/clearrect/index.html @@ -0,0 +1,189 @@ +--- +title: CanvasRenderingContext2D.clearRect() +slug: Web/API/CanvasRenderingContext2D/clearRect +translation_of: Web/API/CanvasRenderingContext2D/clearRect +--- +
{{APIRef}}
+ +

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。

+ +

語法

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

參數

+ +
+
x
+
The x axis of the coordinate for the rectangle starting point.
+
y
+
The y axis of the coordinate for the rectangle starting point.
+
width
+
The rectangle's width.
+
height
+
The rectangle's height.
+
+ +

Usage notes

+ +

A 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.

+ +

範例

+ +

Using the clearRect method

+ +

This is just a simple code snippet which uses the clearRect method.

+ +

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);
+
+
+ +

{{ EmbedLiveSample('Playable_code', 700, 400) }}

+ +

規範

+ + + + + + + + + + + + + + +
SpecificationStatusComment
{{SpecName('HTML WHATWG', "scripting.html#dom-context-2d-clearrect", "CanvasRenderingContext2D.clearRect")}}{{Spec2('HTML WHATWG')}} 
+ +

瀏覽器相容性

+ +

{{CompatibilityTable}}

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+ + + + + + + + + + + + + + + + + + + + + +
FeatureChromeEdgeFirefox (Gecko)Internet ExplorerOperaSafari
Basic support{{CompatVersionUnknown}}{{CompatVersionUnknown}}{{CompatVersionUnknown}}{{CompatVersionUnknown}}{{CompatVersionUnknown}}{{CompatVersionUnknown}}
+
+ +
+ + + + + + + + + + + + + + + + + + + + + + + +
FeatureAndroidChrome for AndroidEdgeFirefox Mobile (Gecko)IE MobileOpera MobileSafari Mobile
Basic support{{CompatVersionUnknown}}{{CompatVersionUnknown}}{{CompatVersionUnknown}}{{CompatVersionUnknown}}{{CompatVersionUnknown}}{{CompatVersionUnknown}}{{CompatVersionUnknown}}
+
+ +

參見

+ + -- cgit v1.2.3-54-g00ecf