If you were short on CPU, you could handle "normal" combining diacritics like 0̩́ in a variety of ways, including just alpha-compositing several glyphs into the

If you were short on CPU, you could handle "normal" combining diacritics like 0̩́ in a variety of ways, including just alpha-compositing several glyphs into the same pixels every time you redraw, and (except for emoji!) you could compute each scan line of a text layer as 8-bit-deep pixelwise coverage first, opening up the possibility of compositing each pixel with bytewise max() rather than alpha-compositing, before mapping those coverages onto pixel colors. But I think the high nibble of the above discussion is that there's quite a bit of performance headroom.