Implement ghost movement and scatter behavior

Each ghost is trying to reach a point beyond the
corner of the board, which make them run in circle

lib/Board.cpp

@@ -23,9 +23,9 @@ static const uint8_t board[ROWS][COLUMNS] = {
   { 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 2, 0, 0, 2, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0 }, // 10
   { 0, 0, 0, 0, 0, 0, 1, 0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0, 0, 1, 0, 0, 0, 0, 0, 0 }, // 11
   { 0, 0, 0, 0, 0, 0, 1, 0, 0, 2, 0, 0, 0, 5, 5, 0, 0, 0, 2, 0, 0, 1, 0, 0, 0, 0, 0, 0 }, // 12
-  { 0, 0, 0, 0, 0, 0, 1, 0, 0, 2, 0, 2, 2, 2, 2, 2, 2, 0, 2, 0, 0, 1, 0, 0, 0, 0, 0, 0 }, // 13
-  { 3, 2, 2, 2, 2, 2, 1, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 0, 2, 2, 2, 1, 2, 2, 2, 2, 2, 3 }, // 14
-  { 0, 0, 0, 0, 0, 0, 1, 0, 0, 2, 0, 2, 2, 2, 2, 2, 2, 0, 2, 0, 0, 1, 0, 0, 0, 0, 0, 0 }, // 15
+  { 0, 0, 0, 0, 0, 0, 1, 0, 0, 2, 0, 5, 5, 5, 5, 5, 5, 0, 2, 0, 0, 1, 0, 0, 0, 0, 0, 0 }, // 13
+  { 3, 2, 2, 2, 2, 2, 1, 2, 2, 2, 0, 5, 5, 5, 5, 5, 5, 0, 2, 2, 2, 1, 2, 2, 2, 2, 2, 3 }, // 14
+  { 0, 0, 0, 0, 0, 0, 1, 0, 0, 2, 0, 5, 5, 5, 5, 5, 5, 0, 2, 0, 0, 1, 0, 0, 0, 0, 0, 0 }, // 15
   { 0, 0, 0, 0, 0, 0, 1, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 1, 0, 0, 0, 0, 0, 0 }, // 16
   { 0, 0, 0, 0, 0, 0, 1, 0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0, 0, 1, 0, 0, 0, 0, 0, 0 }, // 17
   { 0, 0, 0, 0, 0, 0, 1, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 1, 0, 0, 0, 0, 0, 0 }, // 18
@@ -57,6 +57,19 @@ bool Board::isWalkableForGhost(Position point, float d, Direction direction) con
   return isWalkable(point, d, direction, false);
 }
 
+bool Board::isWalkable(Position point) const {
+     return board_state[int(point.y)][int(point.x)] != uint8_t(Cell::wall);
+}
+
+bool Board::isWalkableForGost(Position point, Position origin) const
+{
+    return isWalkable(point) && (isInPen(origin) || !isInPen(point));
+}
+
+bool Board::isInPen(Position point) const {
+    return board_state[int(point.y)][int(point.x)] == uint8_t(Cell::pen);
+}
+
 bool Board::isWalkable(Position point, float position_delta, Direction direction, bool pacman) const {
   if (point.x <= 0 || point.x >= COLUMNS - 1)
     return true;
@@ -77,7 +90,7 @@ bool Board::isWalkable(Position point, float position_delta, Direction direction
     }
   };
   Cell cell = Cell(cellAtPosition(point, position_delta, direction));
-  return pacman ? cell != Cell::wall : cell != Cell::wall && cell != Cell::pen_door;
+  return pacman ? cell != Cell::wall : cell != Cell::wall && cell != Cell::pen;
 }
 
 std::vector<PositionInt> Board::initialPelletPositions() const {

lib/Board.hpp

@@ -18,7 +18,7 @@ public:
     nothing = 2,
     door = 3,
     power_pellet = 4,
-    pen_door = 5,
+    pen = 5,
   };
 
   Board();
@@ -26,6 +26,10 @@ public:
   [[nodiscard]] bool isWalkableForPacMan(Position point, float d, Direction direction) const;
   [[nodiscard]] bool isWalkableForGhost(Position point, float d, Direction direction) const;
 
+  [[nodiscard]] bool isWalkableForGost(Position point, Position origin) const;
+  [[nodiscard]] bool isWalkable(Position point) const;
+  [[nodiscard]] bool isInPen(Position point) const;
+
   [[nodiscard]] std::vector<PositionInt> initialPelletPositions() const;
 
   [[nodiscard]] std::vector<PositionInt> initialSuperPelletPositions() const;
@@ -33,7 +37,9 @@ public:
   static Position initialPacManPosition() { return { 13.5, 23 }; }
 
   static Position initialBlinkyPosition() { return { 13.5, 11 }; }
-  static Position blinkyScatterTarget() { return { 25, -2 }; }
+  static Position penDoorPosition() { return { 13, 11 }; }
+
+  static Position blinkyScatterTarget() { return { 25, -3 }; }
 
   static Position initialSpeedyPosition() { return { 11.5, 14 }; }
   static Position speedyScatterTarget() { return { 3, -2 }; }

lib/Direction.hpp

@@ -7,3 +7,15 @@ enum class Direction {
   UP,
   DOWN
 };
+
+inline Direction oppositeDirection(Direction d)
+{
+    switch (d) {
+        case Direction::LEFT: return Direction::RIGHT;
+        case Direction::RIGHT: return Direction::LEFT;
+        case Direction::UP: return Direction::DOWN;
+        case Direction::DOWN: return Direction::UP;
+        case Direction::NONE: return d;
+    }
+    return d;
+}

lib/Ghost.cpp

@@ -17,15 +17,86 @@ Position Ghost::position() const {
 }
 
 Position Ghost::positionInGrid() const {
-  return { std::round(pos.x), std::round(pos.y) };
+    return { std::round(pos.x), std::round(pos.y) };
 }
 
 void Ghost::update(std::chrono::milliseconds time_delta, const Board & board) {
-  time += time_delta.count();
-  if (time >= 250) {
-    time = 0;
-    alternate_animation = !alternate_animation;
-  }
+    updateAnimation(time_delta);
+    updatePosition(time_delta, board);
+}
+
+void Ghost::updatePosition(std::chrono::milliseconds time_delta, const Board & board) {
+    updateDirection(board);
+
+    float position_delta = (0.004 * time_delta.count()) * 0.75;
+
+    switch (direction) {
+      case Direction::NONE:
+        break;
+      case Direction::LEFT:
+        pos.x -= position_delta;
+        pos.y = round(pos.y);
+        break;
+      case Direction::RIGHT:
+        pos.x += position_delta;
+        pos.y = round(pos.y);
+        break;
+      case Direction::UP:
+        pos.x = round(pos.x);
+        pos.y -= position_delta;
+        break;
+      case Direction::DOWN:
+        pos.x = round(pos.x);
+        pos.y += position_delta;
+        break;
+    }
+}
+
+void Ghost::updateDirection(const Board & board) {
+    auto cell  = positionInGrid();
+    if(cell == lastIntersection)
+        return;
+
+    using P = std::tuple<Direction, Position, double>;
+
+    auto [x , y] = cell;
+    std::array<P, 4> positions = {{
+        P{Direction::UP,    {x, y-1}, 0},
+        P{Direction::LEFT,  {x-1, y}, 0},
+        P{Direction::DOWN,  {x, y+1}, 0},
+        P{Direction::RIGHT, {x+1, y}, 0}
+    }};
+    const Position target = this->target(board);
+
+    std::for_each(positions.begin(), positions.end(), [&](P & p) {
+        get<2>(p) = (get<0>(p) != oppositeDirection(direction) && board.isWalkableForGost(get<1>(p), cell)) ?
+                   std::hypot(get<1>(p).x - target.x, get<1>(p).y - target.y)
+                 : std::numeric_limits<double>::infinity();
+    });
+
+    auto it = std::min_element(positions.begin(), positions.end(), [](const auto & a, const auto &b)
+    {
+        return get<2>(a) < get<2>(b);
+    });
+
+    lastIntersection = cell;
+    direction = std::get<0>(*it);
+}
+
+Position Ghost::target(const Board & board) const {
+    if(board.isInPen(positionInGrid()))
+        return board.penDoorPosition();
+
+    return scatterTarget;
+}
+
+void Ghost::updateAnimation(std::chrono::milliseconds time_delta)
+{
+    time += time_delta.count();
+    if (time >= 250) {
+      time = 0;
+      alternate_animation = !alternate_animation;
+    }
 }
 
 Blinky::Blinky(const Board & board)

lib/Ghost.hpp

@@ -25,6 +25,12 @@ public:
 
   void update(std::chrono::milliseconds time_delta, const Board & board);
 
+private:
+  void updateAnimation(std::chrono::milliseconds time_delta);
+  void updatePosition(std::chrono::milliseconds time_delta, const Board & board);
+  void updateDirection(const Board & board);
+  Position target(const Board & board) const;
+
 protected:
   Atlas::Ghost spritesSet;
   Direction direction = Direction::NONE;
@@ -34,6 +40,7 @@ protected:
   Position pos;
   Position startingPosition;
   Position scatterTarget;
+  Position lastIntersection = {-1, -1};
 };
 
 class Blinky : public Ghost {