updateScrollValues(x, y) {
        // get our scroll delta values
        const lastScrollXValue = this.xOffset;
        this.xOffset = x;
        this.lastXDelta = lastScrollXValue - this.xOffset;

        const lastScrollYValue = this.yOffset;
        this.yOffset = y;
        this.lastYDelta = lastScrollYValue - this.yOffset;

        if(this.onScroll) {
            this.onScroll(this.lastXDelta, this.lastYDelta);
        }
    }
Updates the scroll manager X and Y scroll values as well as last X and Y deltas
     Internally called by the scroll handler
     Could be called externally as well if the user wants to handle the scroll by himself

     params:
     @x (float): scroll value along X axis
     @y (float): scroll value along Y axis
*