`centeredRotation` and `centeredScaling` for programmatic use.

programatic_scale_rotate.js

(function() {
  canvas = this.__canvas;

  canvas.__eventListener = null;

  fabric.Object.prototype.transparentCorners = false;

  var $ = function(id){return document.getElementById(id)};

  var rect = canvas.item(0);

  var angleControl = $('angle-control');
  angleControl.onchange = function() {
    var reset = false;

    if ((rect.originX !== 'center' || rect.originY !== 'center') && (canvas.centeredRotation || rect.centeredRotation)) {
      rect.setOriginToCenter && rect.setOriginToCenter();
      reset = true;
    }

    rect.setAngle(parseInt(this.value, 10)).setCoords();

    if (reset) {
      rect.setCenterToOrigin && rect.setCenterToOrigin();
    }

    canvas.renderAll();
  };

  var scaleControl = $('scale-control');
  scaleControl.onchange = function() {
    var reset = false;

    if ((rect.originX !== 'center' || rect.originY !== 'center') && (canvas.centeredScaling || rect.centeredScaling)) {
      rect.setOriginToCenter && rect.setOriginToCenter();
      reset = true;
    }

    rect.scale(parseFloat(this.value)).setCoords();

    if (reset) {
      rect.setCenterToOrigin && rect.setCenterToOrigin();
    }

    canvas.renderAll();
  };

  var topControl = $('top-control');
  topControl.onchange = function() {
    rect.setTop(parseInt(this.value, 10)).setCoords();
    canvas.renderAll();
  };

  var leftControl = $('left-control');
  leftControl.onchange = function() {
    rect.setLeft(parseInt(this.value, 10)).setCoords();
    canvas.renderAll();
  };

  function updateControls() {
    scaleControl.value = rect.getScaleX();
    angleControl.value = rect.getAngle();
    leftControl.value = rect.getLeft();
    topControl.value = rect.getTop();
  }
  canvas.on({
    'object:moving': updateControls,
    'object:scaling': updateControls,
    'object:resizing': updateControls,
    'object:rotating': updateControls
  });


  fabric.Object.prototype.setOriginToCenter = function() {
    this._originalOriginX = this.originX;
    this._originalOriginY = this.originY;

    var center = this.getCenterPoint();

    this.set({
      originX: 'center',
      originY: 'center',
      left: center.x,
      top: center.y
    });
  };

  fabric.Object.prototype.setCenterToOrigin = function() {
    var originPoint = this.translateToOriginPoint(
      this.getCenterPoint(),
      this._originalOriginX,
      this._originalOriginY);

    this.set({
      originX: this._originalOriginX,
      originY: this._originalOriginY,
      left: originPoint.x,
      top: originPoint.y
    });
  };

})();

Hi, der Gist hier ist zwar schon etwas älter, aber falls du interessiert wärst beruflich etwas in dieser Richtung bei einem neuen Arbeitgegber zu machen, dann schau mal auf LinkedIn nach meiner Kontaktanfrage.