Calculated bounding box size depends on the autoFitMode. Possible values are:
ImGearARTTextAutoFitMode.AdjustHeight - in this mode the width remains unchanged, the height is adjusted to fit entire text without clipping.
ImGearARTTextAutoFitMode.AdjustWidth - in this mode the height remains unchanged, the width is adjusted to fit the widest text line without clipping from the right.