in src/shapes/shapes.ts [87:92]
export function offset(rect: IRect, offsetX: number, offsetY: number): IRect {
let newLeft = ((rect.left + offsetX) >= 0) ? rect.left + offsetX : 0;
let newTop = ((rect.top + offsetY) >= 0) ? rect.top + offsetY : 0;
return { left: newLeft, top: newTop, width: rect.width, height: rect.height };
}