Possible to override bounding box selection area in fabricjs - controls option

Question

Here, we are working in fabric.js with creating design tool.We have create custom selection area for canvas object in fabric.js. I read source code in fabric.js, it generates square box for bounding box, but I want change to my custom. Selection area appearance. Can someone please advise me?

We want custom selection area appearance.

We have tried this code context.setLineDash() for selection area.

if (fabric.StaticCanvas.supports('setLineDash') === true) {
    ctx.setLineDash([4, 4]);
}

Refer code from Github.But won`t working fine for my working area.

Here we have attached Borderdasharray Property creation in fabric function

fabric.Object.prototype.set({  
        borderColor: 'green',  
        cornerColor: 'purple',  
        cornerSize: 33,
        transparentCorners: false,padding:4,
        borderDashArray:[50,25]          
    });

But we need to create animated dancing dots/moving dots for that selection area in fabric.js.

How can we create custom selection area in fabric.js?

Answer 1

For an animated "borderDashArray", the MDN Documentation on lineDashOffset provides a Marching Ants example with the following (fiddle demo) :

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var offset = 0;

function draw() {
  ctx.clearRect(0,0, canvas.width, canvas.height);
  ctx.setLineDash([4, 2]);
  ctx.lineDashOffset = -offset;
  ctx.strokeRect(10,10, 100, 100);
}

function march() {
  offset++;
  if (offset > 16) {
    offset = 0;
  }
  draw();
  setTimeout(march, 20);
}

march();

Based on fabricjs object_interactivity.mixin.js drawBorders function, the above can be applied as follows :

fabric.Object.prototype.set({  
        borderColor: 'green',  
        cornerColor: 'purple',  
        cornerSize: 33,
        transparentCorners: false,padding:14,
        borderDashArray:[50,25]          
    });
// initialize fabric canvas and assign to global windows object for debug
var canvas = window._canvas = new fabric.Canvas('c',{width: 500, height: 500});
textbox = new fabric.Textbox('Hello, World!', {
  width: 200,
  height: 200,
  top: 80,
  left: 80,
  fontSize: 50,
  textAlign: 'center',
});
canvas.add(textbox);
textbox2 = new fabric.Textbox('Hello, World!', {
  width: 200,
  height: 200,
  top: 160,
  left: 160,
  fontSize: 50,
  textAlign: 'center',
});
canvas.add(textbox2);
canvas.renderAll();
canvas.setActiveObject(textbox);
var offset = 0;

  (function animate() {
    offset++;
    if (offset > 75) {
      offset = 0;
    }  
    canvas.contextContainer.lineDashOffset = -offset;
    canvas.renderAll();
    fabric.util.requestAnimFrame(animate);
  })();

  canvas.on('after:render', function() {
    canvas.contextContainer.strokeStyle = 'green';
        canvas.contextContainer.setLineDash([50,25]);
    canvas.forEachObject(function(obj) {
      var bound = obj.getBoundingRect();            
      canvas.contextContainer.strokeRect(
        bound.left + 0.5,
        bound.top + 0.5,
        bound.width,
        bound.height
      );
    })
  });

fabricjs border animation fiddle demo.

Answer 2

For customization :

  borderDashArray: Dash stroke of borders
  cornerDashArray: Dash stroke of corners
  cornerStrokeColor: If corners are filled, this property controls the color of the stroke
  cornerStyle: standrd 'rect' or 'circle'
  selectionBackgroundColor: add an opaque or transparent layer to the selected object.

For use this :

fabric.Object.prototype.set({
    transparentCorners: false,
    borderDashArray: ......