> A type renderer will cache the bitmaps for each individual letter so it only needs to calculate the vector to bitmap activity once for each individual glyph
you mean subpixel antialiasing. but yes, as it turns out, type renderers do cache subpixel-antialiased pixmaps. the part where this gets tricky is with subpixel positioning of the antialiased letterforms, but you can cache them in that case too if you quantize the positioning, even if you don't quantize it to entire pixels