Espruino on P8 smartwatch - ST7789 display driver in Inline C

it was faster which makes me believe that it should be possible to speed up lcd_spi_unbuf

one trick I use is the 12bit color mode which cannot be used for single pixels (2 pixels are stored in 3 bytes). it makes 30ms difference in fullscreen update. The number doesn't look high but if you try both you'll clearly see the difference.

which has the advantage of flexibility in terms of screen buffering

Well, the flexibility could be there too with separate smaller Graphics arraybuffers. If you pre-render stuff into images for speed you are mostly doing same stuff. The native inline code can be simply called with colormap, bitmap rectangle and bpp/stride so can possibly draw also partial areas (that's what it is is already doing - it redraws only modified parts) without any fullscreen buffer and possibly of different bit depths each.