演示
适用于最新的 chrome/firefox。Chrome 实现很简单。Firefox 有限制,用户必须给出命令才能像键盘事件一样进行粘贴,并且可编辑的输入必须被聚焦,所以我们在这里做一些技巧 - 在 ctrl 下我们聚焦输入字段,在释放 unfocus 时。
HTML:
<canvas style="border:1px solid grey;" id="my_canvas" width="300" height="300"></canvas>
JS:
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 reading_dom = false;
var text_top = 15;
var pasteCatcher;
var paste_mode;
//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 - prepare
this.init = function () {
//if using auto
if (window.Clipboard)
return true;
pasteCatcher = document.createElement("div");
pasteCatcher.setAttribute("id", "paste_ff");
pasteCatcher.setAttribute("contenteditable", "");
pasteCatcher.style.cssText = 'opacity:0;position:fixed;top:0px;left:0px;';
pasteCatcher.style.marginLeft = "-20px";
pasteCatcher.style.width = "10px";
document.body.appendChild(pasteCatcher);
document.getElementById('paste_ff').addEventListener('DOMSubtreeModified', function () {
if (paste_mode == 'auto' || ctrl_pressed == false)
return true;
//if paste handle failed - capture pasted object manually
if (pasteCatcher.children.length == 1) {
if (pasteCatcher.firstElementChild.src != undefined) {
//image
_self.paste_createImage(pasteCatcher.firstElementChild.src);
}
}
//register cleanup after some time.
setTimeout(function () {
pasteCatcher.innerHTML = '';
}, 20);
}, false);
}();
//default paste action
this.paste_auto = function (e) {
paste_mode = '';
pasteCatcher.innerHTML = '';
var plain_text_used = false;
if (e.clipboardData) {
var items = e.clipboardData.items;
if (items) {
paste_mode = 'auto';
//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;
}
//c
if (k == 86) {
if (document.activeElement != undefined && document.activeElement.type == 'text') {
//let user paste into some input
return false;
}
if (ctrl_pressed == true && !window.Clipboard)
pasteCatcher.focus();
}
};
//on kaybord release
this.on_keyboardup_action = function (event) {
k = event.keyCode;
//ctrl
if (k == 17 || event.metaKey || event.ctrlKey || event.key == 'Meta')
ctrl_pressed = false;
};
//draw image
this.paste_createImage = function (source) {
var pastedImage = new Image();
pastedImage.onload = function () {
if(autoresize == true){
//resize canvas
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;
};
}
Safari 没有实现 DataTransfer.items,因此无法在 Javascript 中提取图像数据(即复制到剪贴板的屏幕截图)。您可以获取复制的文件,但不能获取数据。
[来自stakeoverflow帖子]