Add quick display update

[memthw]

Added quick update for display based on #1 by removing epd_clear() from every draw and draw a white screen based on buffer. This will reduce the black/white flashing. The epd_clear() is called it only every n-th draw to prevent ghosting.

There are two new option full_update_every and quick_updating.

Name	Type	Default	Description
quick_updating	bool	false	Toggle the quick updating function.
full_update_every	int	5	Sets how many draws will be done before full clear using epd_clear().

It still won't work for Black on White

Sample config:

display:
  - platform: t547
    id: t547_display
    quick_updating: true
    full_update_every: 5

[nickolay]

This caused permanent ghosting for me after just a few cycles This is how the unit looks after running screen_repair and leaving it powered on. Does this not happen to you? Do you know if this can be fixed?

[memthw]

It is happening to me too. But it is only happening when the display power supply is off (epd_poweroff_all()). When the power supply is on (by commenting the last line in screen_repair it is okay. And it mostly went away after few cycles of screen_repair.

This is my first e-ink display and I don't know if it can cause damage to display.

I will try to find a solution to this and I'll have a look how to do a partial updates properly without this issue.

EDIT: It is completely gone after few epd_clear()

[nickolay]

I dunno about “a few” clears, but indeed ghosting is noticeably reduced as I run epd_clear / screen_repair multiple times. The vendor warns that not all “afterimages” can be fixed this way, so I wouldn’t run in this mode for a long time.

(You’re right that ghosting on a powered off display becomes most obvious, but for me it was noticeable during normal operation as well.)

Here people talk about using inverted images instead of 3x black-white flashing: https://github.com/vroland/epdiy/issues/30

But they also recommend using a different epaper in other issues, so I didn’t experiment with such advanced techniques.