Add EPD 4in2bc support

[yurinnick]

So... Does it work? Well, mostly. Display works fine as far as I can tell, however color coding is broken. For some reason 4in2bc uses a completely different scheme than anything implemented.

// 4in2bc
// White bw - 0xFF c - 0xFF
// Black bw - 0 c - 0xFF
// Red bw - 0 c - 0

// bwrbit = true
// White: bw - 0xFF c - 0
// Black: bw - 0 c - 0
// Red: bw - 0 c - 0xFF

// bwrbit = false
// White: bw - 0xFF c - 0
// Black: bw - 0 c - 0
// Red: bw - 0xFF c - 0xFF

@caemor could you help with extending TriColor implementation to match these requirements? I am willing to do it myself, let's just agree on the best way to approach it. Thanks!

[yurinnick]

After this modification colors render correctly. I need to look how to integrate it with current implementation.

impl ColorType for TriColor {
    const BITS_PER_PIXEL_PER_BUFFER: usize = 1;
    const BUFFER_COUNT: usize = 2;

    fn bitmask(&self, bwrbit: bool, pos: u32) -> (u8, u16) {
        let bit = 0x80 >> (pos % 8);
        let mask = match self {
            TriColor::Black => (bit as u16) << 8,
            TriColor::White => (bit as u16) << 8 | bit as u16,
            TriColor::Chromatic => 0u16,
        };
        (!bit, mask)
    }
}

[yurinnick]

Also, update_partial_frame() doesn't work for whatever reason.

[simon0356]

Hello Yurinnick,
I was working on an implementation on the same screen and got the same issue about the chromatic buffer which is inverted.
I have tested your implementation and can confirm it is working on EPD4IN2bc screen
As a reference i use the EPD_4in2b_V2 example code from Waveshare here : https://github.com/waveshare/e-Paper

Thanks for your work,
Simon

[struckoff]

Sup guys, any plans on releasing this one?

[yurinnick]

@caemor could you provide feedback please?

[piedoom]

Is there any additional work that needs to be done for this to be merged in, or any help needed? I would love to use this on main.

[vojty]

I rebased and fixed this PR which I use for my project and created another one here #231