问题
How can I drop items (like image, or other object from other canvas) into canvas which is managed by fabricjs? I have found many examples how to move items inside canvas but I would like to drag and drop item from outer element into canvas.
回答1:
Since you asked for an example and I haven't tried it out myself yet, here goes:
Example Fiddle
Markup
<div id="images">
<img draggable="true" src="http://i.imgur.com/8rmMZI3.jpg" width="250" height="250"></img>
<img draggable="true" src="http://i.imgur.com/q9aLMza.png" width="252" height="295"></img>
<img draggable="true" src="http://i.imgur.com/wMU4SFn.jpg" width="238" height="319"></img>
</div>
<div id="canvas-container">
<canvas id="canvas" width="800" height="600"></canvas>
</div>
JS Breakdown
1. Fabric.canvas instance
First we want our canvas, of course:
var canvas = new fabric.Canvas('c');
2. Feature Detection (optional)
Not sure this is necessary, since the fact that you have a canvas makes it very likely that the browser has Drag and Drop as well. Were you to use it, you can do so like this, using Modernizr:
if (Modernizr.draganddrop) {
// Browser supports HTML5 DnD.
// Bind the event listeners for the image elements
// Bind the event listeners for the canvas
} else {
// Replace with a fallback to a library solution.
alert("This browser doesn't support the HTML5 Drag and Drop API.");
}
3. Events
Again, unlike the source article I below, the source and target elements are different (in that articles's example, you just move divs around within the same parent container), so I failed to notice that some of the events are meant for the element being dragged, but most are bound to the element into which you are dropping.
NOTE: I know this is technically a question about Fabric.js, but it's really kind of a question about Drag and Drop in the context of adding objects to a <canvas> with Fabric.js, which is why I'm going a bit more in depth about the DnD stuff now.
For the <img>
dragstart(I added a class here to lower the opacity)dragend(and removed that class here)
For #canvas-container:
dragenter(added a class to give the canvas container that nifty dotted line)dragover: Here you can set theevent.dataTransfer.dropEffectproperty to show one of the native cursor types. The default would be'move'here, but I set it to'copy'since I don't actually remove the<img>element (in fact in the fiddle you can, for example create several McClures).dragleave(removed the dotted line here)drop: The handler for this event creates and adds thefabric.Imageobject (see the fiddle).
if (Modernizr.draganddrop) {
// Browser supports HTML5 DnD.
// Bind the event listeners for the image elements
var images = document.querySelectorAll('#images img');
[].forEach.call(images, function (img) {
img.addEventListener('dragstart', handleDragStart, false);
img.addEventListener('dragend', handleDragEnd, false);
});
// Bind the event listeners for the canvas
var canvasContainer = document.getElementById('canvas-container');
canvasContainer.addEventListener('dragenter', handleDragEnter, false);
canvasContainer.addEventListener('dragover', handleDragOver, false);
canvasContainer.addEventListener('dragleave', handleDragLeave, false);
canvasContainer.addEventListener('drop', handleDrop, false);
} else {
// Replace with a fallback to a library solution.
alert("This browser doesn't support the HTML5 Drag and Drop API.");
}
Sources:
- HTML5 Rocks - Native HTML5 Drag and Drop
- Modernizr
- Web Platform Docs > DOM > Properties - dropEffect
- Web Platform Docs > DOM > Events
- dragstart
- dragend
- dragenter
- dragover
- dragleave
- drop
回答2:
I had gone through fiddle of @natchiketa, And fixed the problem , just check this fiddle..
http://jsfiddle.net/Ahammadalipk/w8kkc/185/
window.onload = function () {
var canvas = new fabric.Canvas('canvas');
/*
NOTE: the start and end handlers are events for the <img> elements; the rest are bound to
the canvas container.
*/
function handleDragStart(e) {
[].forEach.call(images, function (img) {
img.classList.remove('img_dragging');
});
this.classList.add('img_dragging');
}
function handleDragOver(e) {
if (e.preventDefault) {
e.preventDefault();
}
e.dataTransfer.dropEffect = 'copy';
return false;
}
function handleDragEnter(e) {
this.classList.add('over');
}
function handleDragLeave(e) {
this.classList.remove('over');
}
function handleDrop(e) {
if (e.stopPropagation) {
e.stopPropagation(); // stops the browser from redirecting.
}
var img = document.querySelector('#images img.img_dragging');
var newImage = new fabric.Image(img, {
width: img.width,
height: img.height,
// Set the center of the new object based on the event coordinates relative
// to the canvas container.
left: e.layerX,
top: e.layerY
});
newImage.hasControls = newImage.hasBorders = false;
canvas.add(newImage);
return false;
}
function handleDragEnd(e) {
// this/e.target is the source node.
[].forEach.call(images, function (img) {
img.classList.remove('img_dragging');
});
}
if (Modernizr.draganddrop) {
var images = document.querySelectorAll('#images img');
[].forEach.call(images, function (img) {
img.addEventListener('dragstart', handleDragStart, false);
img.addEventListener('dragend', handleDragEnd, false);
});
var canvasContainer = document.getElementById("canvas-container");
canvasContainer.addEventListener('dragenter', handleDragEnter, false);
canvasContainer.addEventListener('dragover', handleDragOver, false);
canvasContainer.addEventListener('dragleave', handleDragLeave, false);
canvasContainer.addEventListener('drop', handleDrop, false);
} else {
alert("This browser doesn't support the HTML5 Drag and Drop API.");
}
}
Thanks
回答3:
Well, the question is quite old^^
I have updateted the fiddle, no it will work in Firefox as well.
Fiddle
function handleDrop(e) {
// this / e.target is current target element.
e.preventDefault(); //I've altert this line for FireFox
来源：https://stackoverflow.com/questions/13868783/drag-and-drop-into-fabric-js-canvas