Jakub de16dbe32a fix(eink): drive the whole panel on every update, not just the changes ...

The screen faded as the device was used: text went grey a few updates
after it was drawn, while whatever had just changed stayed crisp. Only a
full refresh brought it back, and the next few updates ate it again.

A partial update is differential -- the controller drives only the pixels
that differ between its "current" (0x24) and "previous" (0x26) RAM and
leaves the rest to hold their own charge, which this panel doesn't do
well. Priming the previous-image RAM with the inverse of the incoming
frame makes every pixel a difference, so all of them get driven to their
target, in both directions.

The inverse matters: priming with flat white makes only white->black a
difference, so ink is re-driven but never erased and every screen ever
shown accumulates as a ghost. Confirmed on hardware, both ways round.

Costs one extra full-screen RAM write (a few ms of SPI). The refresh
itself is unchanged -- the waveform clocks the whole panel regardless of
how many pixels it drives -- so nothing got slower. Clearing ghosts is
still the periodic full refresh's job (Settings > Full rfsh), which can
now stay off.

The helper needs GxEPD2_BW's private _buffer/_page_height, so it goes in
the patched copy of the header, which every e-ink build now includes
unconditionally rather than only screenshot-enabled ones. All e-ink
variants pin GxEPD2 1.6.2, the version that copy tracks.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

2026-07-28 15:02:28 +02:00

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fix(eink): drive the whole panel on every update, not just the changes

2026-07-28 15:02:28 +02:00