FabricJS image object clipTo shape object issue

问题

Why this clipTo method doesn't work on the latest fabricjs version, which you could resize the object container and the image inside it. Also you able to move the container object and image object.

   var imgInstance = new fabric.Image(img, {
                width: instanceWidth,
                height: instanceHeight,
                top: (canvas.getHeight() / 2 - instanceHeight / 2),
                left: (canvas.getWidth() / 2 - instanceWidth / 2),
                originX: 'left',
                originY: 'top'
            });
            canvas.add(imgInstance);
            imgInstance.clipTo = function(ctx) {
                /* image clipping method doesn't work on latest fabricjs version*/
                ctx.save();
                ctx.setTransform(1, 0, 0, 1, 0, 0);

                clippingRect.render(ctx);

                ctx.restore();
            };

http://jsfiddle.net/efmbrm4v/2/

Or is their another approach shape object inside is the image object.

回答1:

There is some caching issue with the latest version of FabricJS. To get around that, you need to set objectCaching property to false for the rectangle object.

$(document).ready(function() {
   var imageLoader = document.getElementById('imageLoader');
   imageLoader.addEventListener('change', handleImage, false);
});

var canvas = new fabric.Canvas('myCanvas');

var clippingRect = new fabric.Rect({
   left: 100,
   top: 100,
   width: 100,
   height: 100,
   fill: 'transparent',
   opacity: 1,
   objectCaching: false //<-- set this
});
canvas.add(clippingRect);

function handleImage(e) {
   var reader = new FileReader();
   reader.onload = function(event) {
      var img = new Image();
      img.onload = function() {

         var instanceWidth, instanceHeight;

         instanceWidth = img.width;
         instanceHeight = img.height;

         var imgInstance = new fabric.Image(img, {
            width: instanceWidth,
            height: instanceHeight,
            top: (canvas.getHeight() / 2 - instanceHeight / 2),
            left: (canvas.getWidth() / 2 - instanceWidth / 2),
            originX: 'left',
            originY: 'top'
         });
         canvas.add(imgInstance);
         imgInstance.clipTo = function(ctx) {
            ctx.save();
            ctx.setTransform(1, 0, 0, 1, 0, 0);

            clippingRect.render(ctx);

            ctx.restore();
         };
         canvas.renderAll();
      };
      img.src = event.target.result;
   };
   reader.readAsDataURL(e.target.files[0]);
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.13/fabric.min.js"></script>
<canvas id="myCanvas" width="400" height="300" style="border: 1px solid black"></canvas>
<br />
<label>Choose a File:</label>
<br/>
<br />
<input type="file" id="imageLoader" name="imageLoader" />
<script src="//code.jquery.com/jquery-1.11.0.min.js"></script>

来源：https://stackoverflow.com/questions/44743369/fabricjs-image-object-clipto-shape-object-issue