e-paper GDE021A1 display

this.scd(this.C.cmd[5], 0x00);

Ahh - I definitely wouldn't do that... it's probably less confusing to just write the actual number in there :) The first option (well, just C.CMD_SOMETHING) works well.

Is that possible with the arraybuffer Graphics instance?

Yes, totally - it's made for exactly this kind of thing. There are even options for some of the really bizarre pixel ordering that some displays use :)

 Graphics.createCallback(
            this.C.DISPLAY_SIZE_X,
            this.C.DISPLAY_SIZE_Y,
            2, {msb:true});

or:

 Graphics.createCallback(
            this.C.DISPLAY_SIZE_X,
            this.C.DISPLAY_SIZE_Y,
            2);

should do it... Then just use g.buffer (which is a standard ArrayBuffer - you may need to use new Uint8Array(g.buffer) on it to get at the data).

Try drawing a diagonal line first (it usually helps to see what's wrong :).