我的代码可用于1张画布。但是我需要此实现才能对canvas 2起作用。
所以我尝试了
var SIGNATURE_2 = new CLIPBOARD_CLASS("signatureCanvas2", true);
问题在于这总是将图像粘贴在第一个画布中，我只需要按Ctrl + V。
仅在画布聚焦或悬停时才粘贴？
////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copy paste Image to Canvas
////////////////////////////////////////////////////////////////////////////////////////////////////////////
var SIGNATURE = new CLIPBOARD_CLASS("signatureCanvas", true);
var SIGNATURE_2 = new CLIPBOARD_CLASS("signatureCanvas2", 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
}
}
};
//on keyboard press
this.on_keyboard_action = function (event) {
var 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;
};
}.signatureCanvas {
border:1px solid #027C8C;
width: 100%;
max-height:200px;
}<canvas id="signatureCanvas" class="signatureCanvas"></canvas>
<canvas id="signatureCanvas2" class="signatureCanvas"></canvas>PS：请仅在Windows上打开截图工具，然后复制粘贴图像进行测试
最佳答案
您可以添加click事件以选择适当的画布：
canvas_ids.forEach(function(canv) {
document.getElementById(canv).addEventListener('click', function (e) {
canvas = document.getElementById(canv);
ctx = document.getElementById(canv).getContext("2d");
}, false);
});
然后，您必须更改CLIPBOARD_CLASS的创建。
var SIGNATURE= new CLIPBOARD_CLASS(["signatureCanvas","signatureCanvas2"], true);
为了确保默认情况下选择了第一个画布，您必须进行以下更改：
var canvas = document.getElementById(canvas_ids[0]);
var ctx = document.getElementById(canvas_ids[0]).getContext("2d");
JSFiddle
关于javascript - 使用不同的参数两次调用函数，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/52889843/