First!

Game/FrameBuffer.cs

@@ -0,0 +1,49 @@
+using System;
+
+unsafe struct FrameBuffer
+{
+    public const int Width = 40;
+    public const int Height = 20;
+    public const int Area = Width * Height;
+
+    fixed char _chars[Area];
+
+    public void SetPixel(int x, int y, char character)
+    {
+        _chars[y * Width + x] = character;
+    }
+
+    public void Clear()
+    {
+        for (int i = 0; i < Area; i++)
+            _chars[i] = ' ';
+    }
+
+    public readonly void Render()
+    {
+        Console.SetCursorPosition(0, 0);
+
+        const ConsoleColor snakeColor = ConsoleColor.Green;
+
+        Console.ForegroundColor = snakeColor;
+
+        for (int i = 1; i <= Area; i++)
+        {
+            char c = _chars[i - 1];
+
+            if (c == '*' || (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z'))
+            {
+                Console.ForegroundColor = c == '*' ? ConsoleColor.Red : ConsoleColor.White;
+                Console.Write(c);
+                Console.ForegroundColor = snakeColor;
+            }
+            else
+                Console.Write(c);
+
+            if (i % Width == 0)
+            {
+                Console.SetCursorPosition(0, i / Width - 1);
+            }
+        }
+    }
+}

Game/Game.cs

@@ -0,0 +1,116 @@
+using System;
+using Thread = System.Threading.Thread;
+
+struct Game
+{
+    enum Result
+    {
+        Win, Loss
+    }
+
+    private Random _random;
+
+    private Game(uint randomSeed)
+    {
+        _random = new Random(randomSeed);
+    }
+
+    private Result Run(ref FrameBuffer fb)
+    {
+        Snake s = new Snake(
+            (byte)(_random.Next() % FrameBuffer.Width),
+            (byte)(_random.Next() % FrameBuffer.Height),
+            (Snake.Direction)(_random.Next() % 4));
+
+        MakeFood(s, out byte foodX, out byte foodY);
+
+        long gameTime = Environment.TickCount64;
+
+        while (true)
+        {
+            fb.Clear();
+
+            if (!s.Update())
+            {
+                s.Draw(ref fb);
+                return Result.Loss;
+            }
+
+            s.Draw(ref fb);
+
+            if (Console.KeyAvailable)
+            {
+                ConsoleKeyInfo ki = Console.ReadKey(intercept: true);
+                switch (ki.Key)
+                {
+                    case ConsoleKey.UpArrow:
+                        s.Course = Snake.Direction.Up; break;
+                    case ConsoleKey.DownArrow:
+                        s.Course = Snake.Direction.Down; break;
+                    case ConsoleKey.LeftArrow:
+                        s.Course = Snake.Direction.Left; break;
+                    case ConsoleKey.RightArrow:
+                        s.Course = Snake.Direction.Right; break;
+                }
+            }
+
+            if (s.HitTest(foodX, foodY))
+            {
+                if (s.Extend())
+                    MakeFood(s, out foodX, out foodY);
+                else
+                    return Result.Win;
+            }
+
+            fb.SetPixel(foodX, foodY, '*');
+
+            fb.Render();
+
+            gameTime += 100;
+
+            long delay = gameTime - Environment.TickCount64;
+            if (delay >= 0)
+                Thread.Sleep((int)delay);
+            else
+                gameTime = Environment.TickCount64;
+        }
+    }
+
+    void MakeFood(in Snake snake, out byte foodX, out byte foodY)
+    {
+        do
+        {
+            foodX = (byte)(_random.Next() % FrameBuffer.Width);
+            foodY = (byte)(_random.Next() % FrameBuffer.Height);
+        }
+        while (snake.HitTest(foodX, foodY));
+    }
+
+    public static void Main()
+    {
+        Console.SetWindowSize(FrameBuffer.Width, FrameBuffer.Height);
+        Console.SetBufferSize(FrameBuffer.Width, FrameBuffer.Height);
+        Console.Title = "See Sharp Snake";
+        Console.CursorVisible = false;
+
+        FrameBuffer fb = new FrameBuffer();
+
+        while (true)
+        {
+            Game g = new Game((uint)Environment.TickCount64);
+            Result result = g.Run(ref fb);
+
+            string message = result == Result.Win ? "You win" : "You lose";
+
+            int position = (FrameBuffer.Width - message.Length) / 2;
+            for (int i = 0; i < message.Length; i++)
+            {
+                fb.SetPixel(position + i, FrameBuffer.Height / 2, message[i]);
+            }
+
+            fb.Render();
+
+            Console.ReadKey(intercept: true);
+        }
+    }
+}

Game/Random.cs

@@ -0,0 +1,11 @@
+struct Random
+{
+    private uint _val;
+
+    public Random(uint seed)
+    {
+        _val = seed;
+    }
+
+    public uint Next() => _val = (1103515245 * _val + 12345) % 2147483648;
+}

Game/Snake.cs

@@ -0,0 +1,137 @@
+struct Snake
+{
+    public const int MaxLength = 30;
+
+    private int _length;
+
+    // Body is a packed integer that packs the X coordinate, Y coordinate, and the character
+    // for the snake's body.
+    // Only primitive types can be used with C# `fixed`, hence this is an `int`.
+    private unsafe fixed int _body[MaxLength];
+
+    private Direction _direction;
+    private Direction _oldDirection;
+
+    public Direction Course
+    {
+        set
+        {
+            if (_oldDirection != _direction)
+                _oldDirection = _direction;
+
+            if (_direction - value != 2 && value - _direction != 2)
+                _direction = value;
+        }
+    }
+
+    public unsafe Snake(byte x, byte y, Direction direction)
+    {
+        _body[0] = new Part(x, y, DirectionToChar(direction, direction)).Pack();
+        _direction = direction;
+        _oldDirection = direction;
+        _length = 1;
+    }
+
+    public unsafe bool Update()
+    {
+        Part oldHead = Part.Unpack(_body[0]);
+        Part newHead = new Part(
+            (byte)(_direction switch
+            {
+                Direction.Left => oldHead.X == 0 ? FrameBuffer.Width - 1 : oldHead.X - 1,
+                Direction.Right => (oldHead.X + 1) % FrameBuffer.Width,
+                _ => oldHead.X,
+            }),
+            (byte)(_direction switch
+            {
+                Direction.Up => oldHead.Y == 0 ? FrameBuffer.Height - 1 : oldHead.Y - 1,
+                Direction.Down => (oldHead.Y + 1) % FrameBuffer.Height,
+                _ => oldHead.Y,
+            }),
+            DirectionToChar(_direction, _direction)
+            );
+
+        oldHead = new Part(oldHead.X, oldHead.Y, DirectionToChar(_oldDirection, _direction));
+
+        bool result = true;
+
+        for (int i = 0; i < _length - 1; i++)
+        {
+            Part current = Part.Unpack(_body[i]);
+            if (current.X == newHead.X && current.Y == newHead.Y)
+                result = false;
+        }
+
+        _body[0] = oldHead.Pack();
+
+        for (int i = _length - 2; i >= 0; i--)
+        {
+            _body[i + 1] = _body[i];
+        }
+
+        _body[0] = newHead.Pack();
+
+        _oldDirection = _direction;
+
+        return result;
+    }
+
+    public unsafe readonly void Draw(ref FrameBuffer fb)
+    {
+        for (int i = 0; i < _length; i++)
+        {
+            Part p = Part.Unpack(_body[i]);
+            fb.SetPixel(p.X, p.Y, p.Character);
+        }
+    }
+
+    public bool Extend()
+    {
+        if (_length < MaxLength)
+        {
+            _length += 1;
+            return true;
+        }
+        return false;
+    }
+
+    public unsafe readonly bool HitTest(int x, int y)
+    {
+        for (int i = 0; i < _length; i++)
+        {
+            Part current = Part.Unpack(_body[i]);
+            if (current.X == x && current.Y == y)
+                return true;
+        }
+
+        return false;
+    }
+
+    private static char DirectionToChar(Direction oldDirection, Direction newDirection)
+    {
+        const string DirectionChangeToChar = "│┌?┐┘─┐??└│┘└?┌─";
+        return DirectionChangeToChar[(int)oldDirection * 4 + (int)newDirection];
+    }
+
+    // Helper struct to pack and unpack the packed integer in _body.
+    readonly struct Part
+    {
+        public readonly byte X, Y;
+        public readonly char Character;
+
+        public Part(byte x, byte y, char c)
+        {
+            X = x;
+            Y = y;
+            Character = c;
+        }
+
+        public int Pack() => X << 24 | Y << 16 | Character;
+        public static Part Unpack(int packed) => new Part((byte)(packed >> 24), (byte)(packed >> 16), (char)packed);
+    }
+
+    public enum Direction
+    {
+        Up, Right, Down, Left
+    }
+}