Snake: Use a queue for the movement inputs.

This makes it a lot less finicky to make rapid moves like staircasing and
sudden turns.

AK/CircularQueue.h

@@ -39,6 +39,9 @@ public:
 
     const T& at(int index) const { return m_elements[(m_head + index) % Capacity]; }
 
+    const T& first() const { return at(0); }
+    const T& last() const { return at(size() - 1); }
+
     class ConstIterator {
     public:
         bool operator!=(const ConstIterator& other) { return m_index != other.m_index; }

Games/Snake/SnakeGame.cpp

@@ -56,11 +56,13 @@ void SnakeGame::timer_event(CTimerEvent&)
     if (m_tail.size() > m_length)
         m_tail.take_last();
 
-    m_head.row += m_vertical_velocity;
+    if (!m_velocity_queue.is_empty())
-    m_head.column += m_horizontal_velocity;
+        m_velocity = m_velocity_queue.dequeue();
 
-    m_last_vertical_velocity = m_vertical_velocity;
+    m_head.row += m_velocity.vertical;
-    m_last_horizontal_velocity = m_horizontal_velocity;
+    m_head.column += m_velocity.horizontal;
+
+    m_last_velocity = m_velocity;
 
     if (m_head.row >= m_rows)
         m_head.row = 0;
@@ -90,31 +92,27 @@ void SnakeGame::keydown_event(GKeyEvent& event)
     switch (event.key()) {
     case KeyCode::Key_A:
     case KeyCode::Key_Left:
-        if (m_last_horizontal_velocity == 1)
+        if (last_velocity().horizontal == 1)
             break;
-        m_vertical_velocity = 0;
+        queue_velocity(0, -1);
-        m_horizontal_velocity = -1;
         break;
     case KeyCode::Key_D:
     case KeyCode::Key_Right:
-        if (m_last_horizontal_velocity == -1)
+        if (last_velocity().horizontal == -1)
             break;
-        m_vertical_velocity = 0;
+        queue_velocity(0, 1);
-        m_horizontal_velocity = 1;
         break;
     case KeyCode::Key_W:
     case KeyCode::Key_Up:
-        if (m_last_vertical_velocity == 1)
+        if (last_velocity().vertical == 1)
             break;
-        m_vertical_velocity = -1;
+        queue_velocity(-1, 0);
-        m_horizontal_velocity = 0;
         break;
     case KeyCode::Key_S:
     case KeyCode::Key_Down:
-        if (m_last_vertical_velocity == -1)
+        if (last_velocity().vertical == -1)
             break;
-        m_vertical_velocity = 1;
+        queue_velocity(1, 0);
-        m_horizontal_velocity = 0;
         break;
     default:
         break;
@@ -149,3 +147,18 @@ void SnakeGame::game_over()
 {
     reset();
 }
+
+void SnakeGame::queue_velocity(int v, int h)
+{
+    if (last_velocity().vertical == v && last_velocity().horizontal == h)
+        return;
+    m_velocity_queue.enqueue({ v, h });
+}
+
+const SnakeGame::Velocity& SnakeGame::last_velocity() const
+{
+    if (!m_velocity_queue.is_empty())
+        return m_velocity_queue.last();
+
+    return m_last_velocity;
+}

Games/Snake/SnakeGame.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <LibGUI/GWidget.h>
+#include <AK/CircularQueue.h>
 
 class SnakeGame : public GWidget {
 public:
@@ -24,18 +25,24 @@ private:
         }
     };
 
+    struct Velocity {
+        int vertical { 0 };
+        int horizontal { 0 };
+    };
+
     void game_over();
     void spawn_fruit();
     bool is_available(const Coordinate&);
+    void queue_velocity(int v, int h);
+    const Velocity& last_velocity() const;
 
     int m_rows { 20 };
     int m_columns { 20 };
 
-    int m_horizontal_velocity { 1 };
+    Velocity m_velocity { 0, 1 };
-    int m_vertical_velocity { 0 };
+    Velocity m_last_velocity { 0, 1 };
 
-    int m_last_horizontal_velocity { 1 };
+    CircularQueue<Velocity, 10> m_velocity_queue;
-    int m_last_vertical_velocity { 0 };
 
     Coordinate m_head;
     Vector<Coordinate> m_tail;