Truetype fonts are more like polygonal vector graphics, less like lines/thicknesses. You generally combine two or more characters into a single glyph via a liga

Truetype fonts are more like polygonal vector graphics, less like lines/thicknesses. You generally combine two or more characters into a single glyph via a ligature. But it doesn't end there. Fonts have a crazy number of different lookup tables that can affect how glyphs are drawn. While not Turing complete they're certainly very close. In Arabic, how the baseline blends affecting the base shape of the glyph, plus lots of kerning rules, etc. would make Arabic very difficult to replicate on a segmented display.