Question

我已尽力找到适用于最新版本Firefox的简单，相关且最新的示例，我真的很挣扎。

标题说真的。我希望用户能够从Windows Paint等编辑器复制部分图像，或使用“打印屏幕”按钮，然后将其粘贴到画布元素中。如果画布调整大小以完全适合粘贴的图像（字面意思），则为奖励点。

如果合理，请避免使用基于Flash或Java的解决方案。

我在Javascript方面还不错，但是对于最新的HTML5功能相对缺乏经验，而且对Canvas元素来说是全新的。请帮忙！

Answer 1

版本2.0 ：更小，更清晰的代码适用于Chrome，Firefox，Edge，Opera。没有更多的黑客。但是如果你需要支持IE和Safari，请检查v1版本。

版本1.0 Chrome实施很简单。 Firefox（和IE）有一些限制，用户必须发出命令来粘贴键盘事件，并且必须集中编辑可编辑的输入，所以我们在这里做一些技巧 - 在ctrl down我们focusthat输入字段，释放unocus。

浏览器支持（图片数据）：

火狐
铬
边缘
IE-11
戏

var CLIPBOARD = new CLIPBOARD_CLASS("my_canvas", true);

/**
 * image pasting into canvas
 * 
 * @param {string} canvas_id - canvas id
 * @param {boolean} autoresize - if canvas will be resized
 */
function CLIPBOARD_CLASS(canvas_id, autoresize) {
	var _self = this;
	var canvas = document.getElementById(canvas_id);
	var ctx = document.getElementById(canvas_id).getContext("2d");
	var ctrl_pressed = false;
	var command_pressed = false;
	var paste_event_support;
	var pasteCatcher;

	//handlers
	document.addEventListener('keydown', function (e) {
		_self.on_keyboard_action(e);
	}, false); //firefox fix
	document.addEventListener('keyup', function (e) {
		_self.on_keyboardup_action(e);
	}, false); //firefox fix
	document.addEventListener('paste', function (e) {
		_self.paste_auto(e);
	}, false); //official paste handler

	//constructor - we ignore security checks here
	this.init = function () {
		pasteCatcher = document.createElement("div");
		pasteCatcher.setAttribute("id", "paste_ff");
		pasteCatcher.setAttribute("contenteditable", "");
		pasteCatcher.style.cssText = 'opacity:0;position:fixed;top:0px;left:0px;width:10px;margin-left:-20px;';
		document.body.appendChild(pasteCatcher);

		// create an observer instance
		var observer = new MutationObserver(function(mutations) {
			mutations.forEach(function(mutation) {
				if (paste_event_support === true || ctrl_pressed == false || mutation.type != 'childList'){
					//we already got data in paste_auto()
					return true;
				}

				//if paste handle failed - capture pasted object manually
				if(mutation.addedNodes.length == 1) {
					if (mutation.addedNodes[0].src != undefined) {
						//image
						_self.paste_createImage(mutation.addedNodes[0].src);
					}
					//register cleanup after some time.
					setTimeout(function () {
						pasteCatcher.innerHTML = '';
					}, 20);
				}
			});
		});
		var target = document.getElementById('paste_ff');
		var config = { attributes: true, childList: true, characterData: true };
		observer.observe(target, config);
	}();
	//default paste action
	this.paste_auto = function (e) {
		paste_event_support = false;
		if(pasteCatcher != undefined){
			pasteCatcher.innerHTML = '';
		}
		if (e.clipboardData) {
			var items = e.clipboardData.items;
			if (items) {
				paste_event_support = true;
				//access data directly
				for (var i = 0; i < items.length; i++) {
					if (items[i].type.indexOf("image") !== -1) {
						//image
						var blob = items[i].getAsFile();
						var URLObj = window.URL || window.webkitURL;
						var source = URLObj.createObjectURL(blob);
						this.paste_createImage(source);
					}
				}
				e.preventDefault();
			}
			else {
				//wait for DOMSubtreeModified event
				//https://bugzilla.mozilla.org/show_bug.cgi?id=891247
			}
		}
	};
	//on keyboard press
	this.on_keyboard_action = function (event) {
		k = event.keyCode;
		//ctrl
		if (k == 17 || event.metaKey || event.ctrlKey) {
			if (ctrl_pressed == false)
				ctrl_pressed = true;
		}
		//v
		if (k == 86) {
			if (document.activeElement != undefined && document.activeElement.type == 'text') {
				//let user paste into some input
				return false;
			}

			if (ctrl_pressed == true && pasteCatcher != undefined){
				pasteCatcher.focus();
			}
		}
	};
	//on kaybord release
	this.on_keyboardup_action = function (event) {
		//ctrl
		if (event.ctrlKey == false && ctrl_pressed == true) {
			ctrl_pressed = false;
		}
		//command
		else if(event.metaKey == false && command_pressed == true){
			command_pressed = false;
			ctrl_pressed = false;
		}
	};
	//draw pasted image to canvas
	this.paste_createImage = function (source) {
		var pastedImage = new Image();
		pastedImage.onload = function () {
			if(autoresize == true){
				//resize
				canvas.width = pastedImage.width;
				canvas.height = pastedImage.height;
			}
			else{
				//clear canvas
				ctx.clearRect(0, 0, canvas.width, canvas.height);
			}
			ctx.drawImage(pastedImage, 0, 0);
		};
		pastedImage.src = source;
	};
}

1. Copy image data into clipboard or press Print Screen <br>
2. Press Ctrl+V (page/iframe must be focused):
<br /><br />
<canvas style="border:1px solid grey;" id="my_canvas" width="300" height="300"></canvas>

Answer 2

ViliusL的答案很好，但对于那些正在寻找一种简单的跨浏览器方式来捕获粘贴图像的人来说

window.addEventListener("paste", async function(e) {
  e.preventDefault();
  e.stopPropagation();
  let file = e.clipboardData.items[0].getAsFile();
  let objectUrl = URL.createObjectURL(file);
  // do something with url here
});

您可能想要进行一些错误检查（例如在ViliusL的答案中），以防他们粘贴的不是图像。根据MDN，clipboardData可在所有现代浏览器中使用。我已经在Chrome和Firefox上进行了测试，它们可以正常工作。

如何让用户在纯Javascript中将剪贴板中的图像数据粘贴到Firefox中的canvas元素中？

2 个答案: