`const ofRectangle& getGlyphBBox() const`

You probably don't want people getting a ref and modifying this.

Also, I think calling this the "Glyph" bounding box is a bit confusing if it is a global bounding box.  The glyph bounding box suggests that it is the bounding box of a specific glyph.  I'd suggest that we call it something like maximum bounding box, or leave it out altogether.