Drag and Drop into Fabric.js canvas

Question

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.

Answer 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 the event.dataTransfer.dropEffect property 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 the fabric.Image object (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