diff --git a/src/bin/dualmaze/main.rs b/src/bin/dualmaze/main.rs
new file mode 100644
index 0000000..5879573
--- /dev/null
+++ b/src/bin/dualmaze/main.rs
@@ -0,0 +1,296 @@
+use std::env::args;
+use std::io::stdout;
+use std::io::Write;
+use std::thread::sleep;
+use std::time::Duration;
+
+use rand::thread_rng;
+use rand::Rng;
+
+use pixelfoo::color::Color;
+use pixelfoo::p2;
+use pixelfoo::point2d::Point2d;
+use pixelfoo::v2;
+use pixelfoo::vec2d::Vec2d;
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+enum Square {
+    Unused,
+    Unknown { prio: i32 },
+    Corridor,
+    Wall,
+    Start,
+    Finish,
+}
+
+impl Square {
+    pub fn is_unknown(&self) -> bool {
+        match self {
+            Square::Unknown { .. } => true,
+            _ => false,
+        }
+    }
+}
+
+struct Board(Vec<Vec<Square>>);
+
+fn send<T: Write>(w: &mut T, board: &Board) -> std::io::Result<()> {
+    for line in &board.0 {
+        for square in line {
+            let c = match square {
+                Square::Unused => Color::black(),
+                Square::Unknown { .. } => Color::black(),
+                Square::Corridor => Color::yellow(),
+                Square::Wall => Color::darkblue(),
+                Square::Start => Color::red(),
+                Square::Finish => Color::green(),
+            };
+            w.write_all(&c.rgb())?;
+        }
+    }
+    w.flush()
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+enum Orientation {
+    Horizontal,
+    Vertical,
+}
+
+impl Board {
+    fn new(board_size: Vec2d, maze_size: Vec2d) -> Board {
+        Board(
+            (0..board_size.y)
+                .map(move |y| {
+                    (0..board_size.x)
+                        .map(|x| {
+                            if x < maze_size.x && y < maze_size.y {
+                                if x == 0 || x == maze_size.x - 1 || y == 0 || y == maze_size.y - 1
+                                {
+                                    Square::Wall
+                                } else if x % 2 != 0 && y % 2 != 0 {
+                                    Square::Corridor
+                                } else {
+                                    Square::Unknown { prio: 0 }
+                                }
+                            } else {
+                                Square::Unused
+                            }
+                        })
+                        .collect::<Vec<_>>()
+                })
+                .collect::<Vec<_>>(),
+        )
+    }
+    fn get(&self, pos: Point2d) -> Square {
+        self.0[pos.y as usize][pos.x as usize]
+    }
+    fn set(&mut self, pos: Point2d, sq: Square) {
+        self.0[pos.y as usize][pos.x as usize] = sq;
+    }
+
+    fn set_orientation(&mut self, desired: Orientation, pos: Point2d) {
+        let sq = self.get(pos);
+        let actual;
+        match sq {
+            Square::Unknown { .. } => {
+                // determine wall orientation
+                if pos.x % 2 == 0 && pos.y % 2 != 0 {
+                    actual = Orientation::Vertical;
+                } else if pos.x % 2 != 0 && pos.y % 2 == 0 {
+                    actual = Orientation::Horizontal;
+                } else {
+                    // not a potential wall, unused
+                    actual = Orientation::Horizontal;
+                }
+                let prio = if actual == desired { -1 } else { 1 };
+                self.set(pos, Square::Unknown { prio });
+            }
+            _ => (),
+        }
+    }
+    fn set_horizontal(&mut self, pos: Point2d) {
+        self.set_orientation(Orientation::Horizontal, pos);
+    }
+    fn set_vertical(&mut self, pos: Point2d) {
+        self.set_orientation(Orientation::Vertical, pos);
+    }
+    fn draw_horizontal_segment(&mut self, pos: Point2d, size: Vec2d) {
+        for x in 0..size.x {
+            let xn = size.x - 1 - x;
+            self.set_horizontal(pos + v2!(x, 0));
+            for y in 1..x.min(xn).min(size.y / 2) + 1 {
+                self.set_horizontal(pos + v2!(x, y));
+                self.set_horizontal(pos + v2!(x, -y));
+            }
+        }
+    }
+    fn draw_vertical_segment(&mut self, pos: Point2d, size: Vec2d) {
+        for y in 0..size.y {
+            let yn = size.y - 1 - y;
+            self.set_vertical(pos + v2!(0, y));
+            for x in 1..y.min(yn).min(size.x / 2) + 1 {
+                self.set_vertical(pos + v2!(x, y));
+                self.set_vertical(pos + v2!(-x, y));
+            }
+        }
+    }
+    fn draw_7_segments(&mut self, pos: Point2d, size: Vec2d, segments: u8) {
+        let length = size.x;
+        let width = size.y;
+        let delta = length + 1;
+        let hsize = v2!(length, width);
+        let vsize = v2!(width, length);
+        if (segments & (1 << 0)) != 0 {
+            self.draw_horizontal_segment(pos + v2!(1, 0), hsize);
+        }
+        if (segments & (1 << 1)) != 0 {
+            self.draw_vertical_segment(pos + v2!(delta, 1), vsize);
+        }
+        if (segments & (1 << 2)) != 0 {
+            self.draw_vertical_segment(pos + v2!(delta, delta + 1), vsize);
+        }
+        if (segments & (1 << 3)) != 0 {
+            self.draw_horizontal_segment(pos + v2!(1, 2 * delta), hsize);
+        }
+        if (segments & (1 << 4)) != 0 {
+            self.draw_vertical_segment(pos + v2!(0, 1), vsize);
+        }
+        if (segments & (1 << 5)) != 0 {
+            self.draw_vertical_segment(pos + v2!(0, delta + 1), vsize);
+        }
+        if (segments & (1 << 6)) != 0 {
+            self.draw_horizontal_segment(pos + v2!(1, delta), hsize);
+        }
+    }
+}
+
+struct Move {
+    from: Point2d,
+    dir: Vec2d,
+    prio: i32,
+}
+
+fn add_move<R>(board: &Board, open: &mut Vec<Move>, rng: &mut R, from: Point2d, dir: Vec2d)
+where
+    R: Rng,
+{
+    if let Square::Unknown { prio } = board.get(from + dir) {
+        open.push(Move {
+            from,
+            dir,
+            prio: prio * 1000 + rng.gen_range(0, 1000),
+        });
+    }
+}
+
+const DEFAULT_ARG: isize = 16;
+
+fn main() -> std::io::Result<()> {
+    let args = args().collect::<Vec<_>>();
+    eprintln!("executing {}", args[0]);
+
+    let x_size = args[1].parse::<usize>().unwrap();
+    let y_size = args[2].parse::<usize>().unwrap();
+    let arg = args[3].parse::<isize>().unwrap_or(DEFAULT_ARG);
+    eprintln!("screen size {}x{}, arg {}", x_size, y_size, arg);
+
+    let mut rng = thread_rng();
+
+    let t_frame = 0.040; // s
+    let delay = Duration::new(0, (1_000_000_000.0 * t_frame) as u32);
+    let mut t_wait = 0.0; // s
+
+    let board_size = v2!(x_size as i32, y_size as i32);
+    // round down to odd size for maze
+    let maze_size = v2!(
+        (board_size.x - 1) / 2 * 2 + 1,
+        (board_size.y - 1) / 2 * 2 + 1
+    );
+
+    let mut board = Board(Vec::new());
+    let mut open = Vec::new();
+    loop {
+        if open.is_empty() {
+            if t_wait > 0.0 {
+                t_wait -= t_frame;
+            } else {
+                t_wait = 60.0; // s
+                board = Board::new(board_size, maze_size);
+
+                // TODO draw stuff in prios
+                let segment_size = v2!(11, 5);
+                board.draw_7_segments(p2!(6, 8), segment_size, 0x06);
+                board.draw_7_segments(p2!(24, 8), segment_size, 0x4f);
+                board.draw_7_segments(p2!(42, 8), segment_size, 0x4f);
+                board.draw_7_segments(p2!(60, 8), segment_size, 0x07);
+
+                // start building walls from the border
+                for x in (2..(maze_size.x - 2)).step_by(2) {
+                    add_move(&board, &mut open, &mut rng, p2!(x, 0), v2!(0, 1));
+                    add_move(
+                        &board,
+                        &mut open,
+                        &mut rng,
+                        p2!(x, maze_size.y - 1),
+                        v2!(0, -1),
+                    );
+                }
+                for y in (2..(maze_size.y - 2)).step_by(2) {
+                    add_move(&board, &mut open, &mut rng, p2!(0, y), v2!(1, 0));
+                    add_move(
+                        &board,
+                        &mut open,
+                        &mut rng,
+                        p2!(maze_size.x - 1, y),
+                        v2!(-1, 0),
+                    );
+                }
+            }
+        }
+
+        // draw maze
+        let work = arg.max(1);
+        let mut count = 0;
+        while !open.is_empty() && count < work {
+            open.sort_unstable_by(|Move { prio: pa, .. }, Move { prio: pb, .. }| pb.cmp(pa));
+            let Move {
+                from: p0,
+                dir: dir0,
+                ..
+            } = open.pop().unwrap();
+
+            let p1 = p0 + dir0;
+            let p2 = p1 + dir0;
+            if board.get(p1).is_unknown() {
+                board.set(p1, Square::Wall);
+                board.set(p2, Square::Wall);
+
+                for dir1 in Vec2d::directions() {
+                    let p3 = p2 + dir1;
+                    let p4 = p3 + dir1;
+                    if board.get(p3).is_unknown() {
+                        if board.get(p4).is_unknown() {
+                            add_move(&board, &mut open, &mut rng, p2, dir1);
+                        } else {
+                            board.set(p3, Square::Corridor);
+                        }
+                    }
+                }
+
+                count += 1;
+            }
+
+            if open.is_empty() {
+                board.set(p2!(1, 1), Square::Start);
+                board.set(p2!(maze_size.x - 2, maze_size.y - 2), Square::Finish);
+            }
+        }
+
+        let mut buf = Vec::with_capacity((board_size.x * board_size.y * 3) as usize);
+        send(&mut buf, &board)?;
+        stdout().write_all(&buf)?;
+        stdout().flush()?;
+        sleep(delay);
+    }
+}