fabric.js rotate object around canvas center smoothly - fabricjs

Question

I try to rotate an object around the canvas center smoothly using a slider,
I use fabric.util.rotatePoint to find the new center point and set the new angle,but it seems not exactly around the center point and the object position is jumping.
https://jsfiddle.net/j0g1tLsb/26/
here is my code doing this:
const canvas = new fabric.Canvas('c', { width: innerWidth, height: innerHeight });
canvas.controlsAboveOverlay = true;
canvas.preserveObjectStacking = true;
const rect = new fabric.Rect({
width: 300,
height: 150,
left: 400,
top: 400,
fill: "lightgray",
originX: 'center',
originY: 'center'
});
const centerPoint = new fabric.Circle({
originX: 'center',
originY: 'center',
top: innerHeight/2,
left: innerWidth/2,
radius: 10,
fill: 'red',
hasControls: false,
selectable:false
});
const log = new fabric.Text('', {
left: 30,
top: 30,
originX: 'left',
originY: 'top',
fontSize: 18,
evented: false,
selectable: false
});
canvas.add(rect, centerPoint, log);
document.getElementById('img-rotation').oninput = function() {
rect.set('angle', this.value);
var posNewCenter = fabric.util.rotatePoint(
rect.getCenterPoint(),
canvas.getVpCenter(),
fabric.util.degreesToRadians(this.value)
);
rect.set({
left: posNewCenter.x,
top: posNewCenter.y,
angle: this.value
});
log.set('text', `angle: ${Math.round(rect.angle)} \nleft: ${rect.left} \ntop: ${rect.top}`);
canvas.requestRenderAll();
};
rect.on('modified', () => {
log.set('text', `angle: ${Math.round(rect.angle)} \nleft: ${rect.left} \ntop: ${rect.top}`);
canvas.renderAll();
});

Answer 1

Your problem is in getting center point from the rectangle every time. You need just set new Point from the original rectangle position.
var posNewCenter = fabric.util.rotatePoint(
new fabric.Point(400, 400), //here is your mistake
canvas.getVpCenter(),
fabric.util.degreesToRadians(this.value)
);
rect.set({
left: posNewCenter.x,
top: posNewCenter.y,
angle: this.value
});
Working fiddle
UPDATE:
In order of the modification of the Rectangle you need to use object:modified event to reassign top and left coordinates.
First of all declare top and left variables and use them inside rectangle object:
let top = 400;
let left = 400;
const rect = new fabric.Rect({
...
left: left,
top: top,
...
targetObj: 'rectangle' //you can use any value or ID, it's only for targeting purpose
});
Then you need to check when object is modified. If event is fired then check if it is rectangle.
canvas.on('object:modified', (e) => {
if (e.target.hasOwnProperty('targetObj') && e.target.targetObj === 'rectangle') {
left = e.target.get('left');
top = e.target.get('top');
}
})
Finally, use left and top variables inside oninput event of the slider:
var posNewCenter = fabric.util.rotatePoint(
new fabric.Point(left, top),
canvas.getVpCenter(),
fabric.util.degreesToRadians(this.value)
);
Working updated fiddle