Copy area of 1st buffer to 2nd buffer

I understand now from your original inquiry that there doesn't appear to be a function available
from the current reference:

https://banglejs.com/reference#l_Bangle_­setLCDMode

Has an attempt been made to take a peek under the covers to see if one may garner any insight
until others may respond?

Just to the right of the function declaration, there is a right facing arrow,
Bangle.setLCDMode →

which when clicked takes one to the source:

https://github.com/espruino/Espruino/blo­b/master/libs/banglejs/jswrap_bangle.c#L­1585

(while that link reference in the docs needs to be updated)

Jump to line 1585 for the 'doublebuffered' section. Traversing the calls to certain functions may require the use of other tools such as VSCode.