From 33058f2b292b3a581333bdfb21b8f671898c5060 Mon Sep 17 00:00:00 2001 From: Peter Bengtsson Date: Tue, 8 Dec 2020 14:40:17 -0500 Subject: initial commit --- .../web/api/htmlcanvaselement/todataurl/index.html | 155 +++++++++++++++++++++ 1 file changed, 155 insertions(+) create mode 100644 files/zh-cn/web/api/htmlcanvaselement/todataurl/index.html (limited to 'files/zh-cn/web/api/htmlcanvaselement/todataurl') diff --git a/files/zh-cn/web/api/htmlcanvaselement/todataurl/index.html b/files/zh-cn/web/api/htmlcanvaselement/todataurl/index.html new file mode 100644 index 0000000000..724c67025f --- /dev/null +++ b/files/zh-cn/web/api/htmlcanvaselement/todataurl/index.html @@ -0,0 +1,155 @@ +--- +title: HTMLCanvasElement.toDataURL() +slug: Web/API/HTMLCanvasElement/toDataURL +translation_of: Web/API/HTMLCanvasElement/toDataURL +--- +
+
+
{{APIRef("Canvas API")}}
+
+
+ +

HTMLCanvasElement.toDataURL() 方法返回一个包含图片展示的 data URI 。可以使用 type 参数其类型，默认为 PNG 格式。图片的分辨率为96dpi。

+ + + +

语法

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

参数

+ +
+
type {{optional_inline}}
+
图片格式，默认为 image/png
+
encoderOptions {{optional_inline}}
+
在指定图片格式为 image/jpeg 或 image/webp的情况下，可以从 0 到 1 的区间内选择图片的质量。如果超出取值范围，将会使用默认值 0.92。其他参数会被忽略。
+
+ +

返回值

+ +

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

+ +

示例

+ +

有如下{{HTMLElement("canvas")}}元素

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

可以用这样的方式获取一个 data-URL

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

设置jpegs图片的质量

+ +
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);
+
+ +

示例：动态更改图片

+ +

可以使用鼠标事件来动态改变图片（这个例子中改变图片灰度）。

+ +

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);
+  }
+}
+ +

规范

+ + + + + + + + + + + + + + + + + + + + + + + + +
规范状态备注
{{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.
+ +

浏览器兼容性

+ + + +

{{Compat("api.HTMLCanvasElement.toDataURL")}}

+ +
+ +

参考

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