无法在创建时翻转Canvas

Question

我正在处理以下代码。为什么我无法在创作时翻转画布？我知道我可以使用CSS来做到这一点，但因为我想用filpped格式下载Canvas所以我想我需要在翻转模式下创建它。

		var sampleImage = document.getElementById("ringoImage"),
				canvas = convertImageToCanvas(sampleImage);
			
			// Actions
			document.getElementById("canvasHolder").appendChild(canvas);
			document.getElementById("pngHolder").appendChild(convertCanvasToImage(canvas));
			
			// Converts image to canvas; returns new canvas element
			function convertImageToCanvas(image) {
				var canvas = document.createElement("canvas");
				canvas.width = image.width;
				canvas.height = image.height;
				canvas.getContext("2d").drawImage(image, 0, 0).scale(-1, 1);

				return canvas;
			}

			// Converts canvas to an image
			function convertCanvasToImage(canvas) {
				var image = new Image();
				image.src = canvas.toDataURL("image/png");
				return image;
			}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<h2>Original Image</h2>
		<img src="http://img.dailymail.co.uk/i/pix/2007/07_03/naniflipAP2607_468x652.jpg" id="ringoImage" />

	<h2>Canvas Image</h2>
	<div id="canvasHolder"></div>
	
	<h2>Canvas -&gt; PNG Image</h2>
	<div id="pngHolder"></div>

Answer 1

要做的三件重要事情： 1）加载图像后开始处理（sampleImage.onload） 2）在添加图像之前翻转画布 3）避免在源img标签上使用crossOrigin =“anonymous”来保存受污染的画布

var sampleImage = document.getElementById("ringoImage");
sampleImage.onload = function() {
var canvas = convertImageToCanvas(sampleImage);
// Actions
document.getElementById("canvasHolder").appendChild(canvas);
document.getElementById("pngHolder").appendChild(convertCanvasToImage(canvas));
};

			// Converts image to canvas; returns new canvas element
			function convertImageToCanvas(image) {
				var canvas = document.createElement("canvas");
				canvas.width = image.width;
				canvas.height = image.height;
        var context = canvas.getContext('2d');
        context.translate(canvas.width, 0);
        context.scale(-1, 1);
        context.drawImage(image, 0, 0);
				
				return canvas;
			}

			// Converts canvas to an image
			function convertCanvasToImage(canvas) {
				var image = new Image();
        image.crossOrigin = "anonymous";
				image.src = canvas.toDataURL("image/png");
        return image;
			}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<h2>Original Image</h2>
		<img crossOrigin="anonymous" src="https://cdn.glitch.com/4c9ebeb9-8b9a-4adc-ad0a-238d9ae00bb5%2Fmdn_logo-only_color.svg?1535749917189%22;" id="ringoImage" />

	<h2>Canvas Image</h2>
	<div id="canvasHolder"></div>
	
	<h2>Canvas -&gt; PNG Image</h2>
	<div id="pngHolder"></div>