This version of the driver uses a screen buffer (4125 bytes) and an image buffer (4000 bytes).
It takes 146ms to render the example clock face with widgets.
73ms to do a g.clear();g.flip() of which g.flip takes 49ms.
However, partial updates are faster as only the modified part of the image buffer is is written to the screen buffer.
The recent commit improves the performance at the expense of a more complex update routine.
It now takes 127ms to render the example with g.flip taking 31ms.
Unrolling the inner loop in update gives:
118ms to render the example with g.flip taking 21 ms.