From 218934fa2ed1c702a6d3923d2aa2cc6b43c48684 Mon Sep 17 00:00:00 2001 From: Peter Bengtsson Date: Tue, 8 Dec 2020 14:43:23 -0500 Subject: initial commit --- .../web/api/htmlcanvaselement/todataurl/index.html | 201 +++++++++++++++++++++ 1 file changed, 201 insertions(+) create mode 100644 files/zh-tw/web/api/htmlcanvaselement/todataurl/index.html (limited to 'files/zh-tw/web/api/htmlcanvaselement/todataurl') diff --git a/files/zh-tw/web/api/htmlcanvaselement/todataurl/index.html b/files/zh-tw/web/api/htmlcanvaselement/todataurl/index.html new file mode 100644 index 0000000000..7a87309580 --- /dev/null +++ b/files/zh-tw/web/api/htmlcanvaselement/todataurl/index.html @@ -0,0 +1,201 @@ +--- +title: HTMLCanvasElement.toDataURL() +slug: Web/API/HTMLCanvasElement/toDataURL +tags: + - API + - Canvas +translation_of: Web/API/HTMLCanvasElement/toDataURL +--- +
+
+
{{APIRef("Canvas API")}}
+
+
+ +

HTMLCanvasElement.toDataURL() 方法回傳含有圖像和參數設置特定格式的 data URIs (預設 PNG). 回傳的圖像解析度為 96 dpi.

+ + + +

表達式

+ +
canvas.toDataURL(type, encoderOptions);
+
+ +

參數

+ +
+
type {{optional_inline}}
+
圖像格式的 {{domxref("DOMString")}}. 預設為 image/png.
+
encoderOptions {{optional_inline}}
+
表示 image/jpeg 或是 image/webp 的圖像品質, 為0 到 1 之間的 {{jsxref("Number")}}.
+ 如果值不在上述範圍中, 將會使用預設值. 其他的會忽略.
+
+ +

回傳值

+ +

包含 data URI 的 {{domxref("DOMString")}}.

+ +

範例

+ +

創建 {{HTMLElement("canvas")}} 元素:

+ +
<canvas id="canvas" width="5" height="5"></canvas>
+
+ +

可以使用下面的方式獲取 data-URL:

+ +
var canvas = document.getElementById("canvas");
+var dataURL = canvas.toDataURL();
+console.log(dataURL);
+// "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNby
+// blAAAADElEQVQImWNgoBMAAABpAAFEI8ARAAAAAElFTkSuQmCC"
+
+ +

設置圖像的品質

+ +
var fullQuality = canvas.toDataURL("image/jpeg", 1.0);
+// data:image/jpeg;base64,/9j/4AAQSkZJRgABAQ...9oADAMBAAIRAxEAPwD/AD/6AP/Z"
+var mediumQuality = canvas.toDataURL("image/jpeg", 0.5);
+var lowQuality = canvas.toDataURL("image/jpeg", 0.1);
+
+ +

範例: 動態改變圖像

+ +

為了動態改變圖像, 可以與滑鼠事件一起使用 (gray-scale versus color in this example):

+ +

HTML

+ +
<img class="grayscale" src="myPicture.png" alt="Description of my picture" />
+ +

JavaScript

+ +
window.addEventListener("load", removeColors);
+
+function showColorImg() {
+  this.style.display = "none";
+  this.nextSibling.style.display = "inline";
+}
+
+function showGrayImg() {
+  this.previousSibling.style.display = "inline";
+  this.style.display = "none";
+}
+
+function removeColors() {
+  var aImages = document.getElementsByClassName("grayscale"),
+      nImgsLen = aImages.length,
+      oCanvas = document.createElement("canvas"),
+      oCtx = oCanvas.getContext("2d");
+  for (var nWidth, nHeight, oImgData, oGrayImg, nPixel, aPix, nPixLen, nImgId = 0; nImgId < nImgsLen; nImgId++) {
+    oColorImg = aImages[nImgId];
+    nWidth = oColorImg.offsetWidth;
+    nHeight = oColorImg.offsetHeight;
+    oCanvas.width = nWidth;
+    oCanvas.height = nHeight;
+    oCtx.drawImage(oColorImg, 0, 0);
+    oImgData = oCtx.getImageData(0, 0, nWidth, nHeight);
+    aPix = oImgData.data;
+    nPixLen = aPix.length;
+    for (nPixel = 0; nPixel < nPixLen; nPixel += 4) {
+      aPix[nPixel + 2] = aPix[nPixel + 1] = aPix[nPixel] = (aPix[nPixel] + aPix[nPixel + 1] + aPix[nPixel + 2]) / 3;
+    }
+    oCtx.putImageData(oImgData, 0, 0);
+    oGrayImg = new Image();
+    oGrayImg.src = oCanvas.toDataURL();
+    oGrayImg.onmouseover = showColorImg;
+    oColorImg.onmouseout = showGrayImg;
+    oCtx.clearRect(0, 0, nWidth, nHeight);
+    oColorImg.style.display = "none";
+    oColorImg.parentNode.insertBefore(oGrayImg, oColorImg);
+  }
+}
+ +

規範

+ + + + + + + + + + + + + + + + + + + + + + + + +
規範狀態註
{{SpecName('HTML WHATWG', "scripting.html#dom-canvas-todataurl", "HTMLCanvasElement.toDataURL")}}{{Spec2('HTML WHATWG')}}No change since the latest snapshot, {{SpecName('HTML5 W3C')}}
{{SpecName('HTML5.1', "scripting-1.html#dom-canvas-todataurl", "HTMLCanvasElement.toDataURL")}}{{Spec2('HTML5.1')}} 
{{SpecName('HTML5 W3C', "scripting-1.html#dom-canvas-todataurl", "HTMLCanvasElement.toDataURL")}}{{Spec2('HTML5 W3C')}}Snapshot of the {{SpecName('HTML WHATWG')}} containing the initial definition.
+ +

瀏覽器相容性

+ +

{{ CompatibilityTable() }}

+ +
+ + + + + + + + + + + + + + + + + + + +
FeatureChromeFirefox (Gecko)Internet ExplorerOperaSafari
Basic support{{ CompatChrome(4) }}{{ CompatGeckoDesktop("1.9.2") }}{{ CompatIE(9) }}{{ CompatOpera(9) }}{{ CompatSafari(4.0) }}
+
+ +
+ + + + + + + + + + + + + + + + + + + + + +
FeatureAndroidChrome for AndroidFirefox Mobile (Gecko)IE MobileOpera MobileSafari Mobile
Basic support{{ CompatAndroid(3.2) }}{{ CompatAndroid(18) }}{{ CompatGeckoMobile("1.9.2") }}{{ CompatVersionUnknown() }}{{ CompatOpera(19) }}{{ CompatSafari(3.0) }}
+
+ +

參見

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