impl Display {
    pub fn clear(&mut self) {
        self.vram = [0x00; SCREEN_HEIGHT * SCREEN_WIDTH * 4];
    }
    // fixme: support alpha channel
    pub unsafe fn set_pixel_greyscale(&mut self, pos: usize, val: u8) {
        // set to unsafe as it does not do any bounds checking
        self.vram
            .iter_mut()
            .skip(pos * 4)
            .take(3)
            .for_each(|pixel| *pixel = val);
        self.vram
            .iter_mut()
            .skip(pos * 4 + 3)
            .take(1)
            .for_each(|pixel| *pixel = 0xFF);
    }
    pub fn set_pixel(&mut self, x: usize, y: usize) -> Result<(), Error> {
        match (x, y) {
            (_, _) if x < 64 && y < 64 => unsafe {
                self.set_pixel_greyscale(x + (SCREEN_WIDTH * y), 0xFF)
            },
            (_, _) if x >= 64 => {
                return Err(Error::InvalidValue(
                    "Value x is too large (was > 63)".to_string(),
                ))
            }
            (_, _) if y > 62 => {
                return Err(Error::InvalidValue(
                    "Value y is too large (was > 31)".to_string(),
                ))
            }
            (_, _) => (),
        }
        Ok(())
    }