I think the terminology you use is not right. Unicode maps integers to graphemes (not glyphs) and vice-versa (i.e. it's a 1-1 mapping). Fonts map graphemes to glyphs.
This is even more wrong. Unicode maps integers to abstract characters. Fonts map characters to glyphs and layout engines map glyphs to graphemes. Keep in mind that graphemes can be composed of multiple parts, e.g. ligratures or combining characters.