@return The desired (general) offset you wish the IMarker to have on the x- and y-axis.
By returning x: -(width / 2) you will center the IMarker horizontally.
By returning y: -(height / 2) you will center the IMarker vertically.
@return The offset for drawing at the specific point. This allows conditional adjusting of the Marker position.
If you have no adjustments to make, return getOffset().