Something like this:

pub trait Interface<P: Copy> {
    type Error: core::fmt::Debug;

    fn send_command(&mut self, command: u8, args: &[u8]) -> Result<(), Self::Error>;

    fn send_pixels(&mut self, pixels: impl Iterator<Item = P>) -> Result<(), Self::Error>;
    
    fn send_repeated_pixel(&mut self, pixel: P, count: u32) -> Result<(), Self::Error> {
        self.send_pixels((0..count).map(|_| pixel))
    }

    fn flush(&mut self) -> Result<(), Self::Error>;
}

In reply to @grantm11235:matrix.org
fill_solid can be optimized without any changes to e-g. You just need to have a medium-sized buffer, fill it with the endian-corrected color, then send/reuse the buffer as many times as you need to in order to complete the fill

In reply to @grantm11235:matrix.org
What if you add a IntoStorage bound?

but technically, if we wanted to be correct, endianness would also have to be "known" as well. Hence my comment on the "color with endianness" types. This will also help in non fill_solid cases beacuse the data from things like Triangle etc. would be prepared for the display, removing the need for to_be().

TBF: I think most displays are BE, so I'd just default to that