encompass-cs-docs

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title	date	weight
Win Condition	2019-06-09T19:10:15-07:00	30

There's one critical element missing from our game. Right now, once the game starts, it keeps going until the player exits the program. We need a win condition, and to indicate when that win condition has been reached.

Our win condition is pretty simple: get x number of points. When one player wins the game, we want to display a message that says they won, and then go back to the title screen.

I've been avoiding it but I think it's time for a UI Text system. All we need to display text is a position, a font, and a string.

In PongFE/Components/UITextComponent.cs

using Encompass;
using SpriteFontPlus;

namespace PongFE.Components
{
    public struct UITextComponent
    {
        public DynamicSpriteFont Font { get; }
        public string Text { get; }

        public UITextComponent(DynamicSpriteFont font, string text)
        {
            Font = font;
            Text = text;
        }
    }
}

In PongFE/Messages/UITextSpawnMessage.cs:

using Encompass;
using MoonTools.Structs;
using SpriteFontPlus;

namespace PongFE.Messages
{
    public struct UITextSpawnMessage
    {
        public Position2D Position { get; }
        public string Text { get; }
        public DynamicSpriteFont Font { get; }

        public UITextSpawnMessage(Position2D position, DynamicSpriteFont font, string text)
        {
            Position = position;
            Font = font;
            Text = text;
        }
    }
}

In PongFE/Engines/Spawners/UITextSpawner.cs:

using Encompass;
using PongFE.Components;
using PongFE.Messages;

namespace PongFE.Spawners
{
    public class UITextSpawner : Spawner<UITextSpawnMessage>
    {
        protected override void Spawn(in UITextSpawnMessage message)
        {
            var entity = CreateEntity();

            AddComponent(entity, new PositionComponent(message.Position));
            AddComponent(entity, new UITextComponent(message.Font, message.Text));
        }
    }
}

Now we need a way to render the text.

In PongFE/Renderers/UITextRenderer.cs:

using Encompass;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using PongFE.Components;
using PongFE.Extensions;
using SpriteFontPlus;

namespace PongFE.Renderers
{
    public class UITextRenderer : Renderer
    {
        private SpriteBatch SpriteBatch { get; }

        public UITextRenderer(SpriteBatch spriteBatch)
        {
            SpriteBatch = spriteBatch;
        }

        public override void Render(double dt, double alpha)
        {
            SpriteBatch.Begin(SpriteSortMode.Deferred, BlendState.Nonpremultiplied);

            foreach (ref readonly var entity in ReadEntities<UITextComponent>())
            {
                ref readonly var uiTextComponent = ref GetComponent<UITextComponent>(entity);
                ref readonly var positionComponent = ref GetComponent<PositionComponent>(entity);

                SpriteBatch.DrawString(
                    uiTextComponent.Font,
                    uiTextComponent.Text,
                    positionComponent.Position.ToXNAVector(),
                    Color.White
                );
            }

            SpriteBatch.End();
        }
    }
}

With that out of the way, let's create a message for winning the game and a message for changing the game state.

In PongFE/Messages/GameWinMessage.cs:

using Encompass;
using PongFE.Enums;

namespace PongFE.Messages
{
    public struct GameWinMessage
    {
        public PlayerIndex PlayerIndex { get; }

        public GameWinMessage(PlayerIndex playerIndex)
        {
            PlayerIndex = playerIndex;
        }
    }
}

In PongFE/Messages/ChangeGameStateMessage.cs:

using Encompass;
using PongFE.Enums;

namespace PongFE.Messages
{
    public struct ChangeGameStateMessage
    {
        public GameState GameState { get; }

        public ChangeGameStateMessage(GameState gameState)
        {
            GameState = gameState;
        }
    }
}

Now we can create an engine that handles winning the game.

In PongFE/Engines/GameWinEngine.cs:

using Encompass;
using PongFE.Components;
using PongFE.Enums;
using PongFE.Messages;
using SpriteFontPlus;

namespace PongFE.Engines
{
    [Reads(typeof(PlayAreaComponent))]
    [Receives(typeof(GameWinMessage))]
    [Sends(typeof(UITextSpawnMessage), typeof(ChangeGameStateMessage))]
    public class GameWinEngine : Engine
    {
        public DynamicSpriteFont Font { get; }
        private readonly string _playerOneWinText = "Player 1 Wins!";
        private readonly string _playerTwoWinText = "Player 2 Wins!";

        public GameWinEngine(DynamicSpriteFont font)
        {
            Font = font;
        }

        public override void Update(double dt)
        {
            if (SomeMessage<GameWinMessage>())
            {
                ref readonly var gameWinMessage = ref ReadMessage<GameWinMessage>();
                ref readonly var playAreaComponent = ref ReadComponent<PlayAreaComponent>();

                string winText;
                if (gameWinMessage.PlayerIndex == PlayerIndex.One)
                {
                    winText = _playerOneWinText;
                }
                else
                {
                    winText = _playerTwoWinText;
                }

                var textDimensions = Font.MeasureString(winText);

                SendMessage(new UITextSpawnMessage(
                    new MoonTools.Structs.Position2D(
                        (playAreaComponent.Width - textDimensions.X) / 2,
                        playAreaComponent.Height / 4
                    ),
                    Font,
                    winText
                ));

                SendMessage(new ChangeGameStateMessage(GameState.Title), 2);
            }
        }
    }
}

Before we move on, I would like to address one lingering concern. Let's try a little exercise. How can we express our game rule about spawning balls in a human sentence?

"We respawn a ball x amount of seconds after a ball is destroyed."

This was fine enough when we didn't have an actual scoring loop. Now we have a problem though - we don't want the ball to be served after the game is won.

What if instead we could think of the rule as being "A ball is served x seconds after a point is scored, unless that point is the winning point of the game." This implies that spawning the ball is the responsibility of the ScoreEngine and not the DestroyEngine.

I think it would be nice to have some component that stores our ball parameters, so we can retrieve them easily.

In PongFE/Components/BallParametersComponent.cs:

using Encompass;

namespace PongFE.Components
{
    public struct BallParametersComponent
    {
        public int Speed { get; }
        public double Delay { get; }

        public BallParametersComponent(int speed, double delay)
        {
            Speed = speed;
            Delay = delay;
        }
    }
}

Now let's modify our ScoreEngine.

using Encompass;
using PongFE.Components;
using PongFE.Messages;

namespace PongFE.Engines
{
    [Reads(
        typeof(ScoreComponent),
        typeof(PlayerComponent),
        typeof(BallParametersComponent)
    )]
    [Receives(typeof(ScoreMessage))]
    [Sends(typeof(GameWinMessage), typeof(BallSpawnMessage))]
    [Writes(typeof(ScoreComponent))]
    public class ScoreEngine : Engine
    {
        public override void Update(double dt)
        {
            foreach (ref readonly var scoreMessage in ReadMessages<ScoreMessage>())
            {
                if (HasComponent<ScoreComponent>(scoreMessage.Entity))
                {
                    ref readonly var scoreComponent = ref GetComponent<ScoreComponent>(scoreMessage.Entity);
                    SetComponent(scoreMessage.Entity, new ScoreComponent(scoreComponent.Score + 1));

                    if (scoreComponent.Score + 1 >= 5)
                    {
                        ref readonly var playerComponent = ref GetComponent<PlayerComponent>(scoreMessage.Entity);
                        SendMessage(new GameWinMessage(playerComponent.PlayerIndex));
                    }
                    else
                    {
                        ref readonly var ballParametersComponent = ref ReadComponent<BallParametersComponent>();

                        SendMessage(
                            new BallSpawnMessage(
                                new MoonTools.Structs.Position2D(640, (int)MathHelper.RandomFloat(20, 700)),
                                ballParametersComponent.Speed,
                                16,
                                16
                            ),
                            ballParametersComponent.Delay
                        );
                    }
                }
            }
        }
    }
}

Notice how easy it was to move the responsibility of spawning the ball without having to worry about complex dependencies. This is a major benefit of loose coupling - we can make fairly fundamental logic changes to the game without having to disentangle functionality across the entire project.

It's always a good idea to take a step back and describe your game rules in human sentences. This can make it very clear how you should organize the responsibilities of your engines.

This means we can get rid of some stuff. There's no need for the SpawnBallAfterDestroyComponent any more, so we can delete that file and all references to that component.

Now let's handle the game state change. We have a UI Text system now, so we can get rid of the TitleRenderer and move that stuff to be handled by GameStateEngine.

In GameStateEngine:

using Encompass;
using Microsoft.Xna.Framework.Input;
using MoonTools.Structs;
using PongFE.Components;
using PongFE.Enums;
using PongFE.Messages;
using SpriteFontPlus;

namespace PongFE.Engines
{
    [Reads(
        typeof(PositionComponent),
        typeof(GameStateComponent),
        typeof(PlayAreaComponent),
        typeof(UITextComponent)
    )]
    [Receives(typeof(ChangeGameStateMessage))]
    [Sends(
        typeof(BallSpawnMessage),
        typeof(PaddleSpawnMessage),
        typeof(BoundarySpawnMessage),
        typeof(GoalBoundarySpawnMessage),
        typeof(UITextSpawnMessage)
    )]
    [Writes(typeof(GameStateComponent))]
    public class GameStateEngine : Engine
    {
        private DynamicSpriteFont TitleFont { get; }
        private DynamicSpriteFont InstructionFont { get; }

        public GameStateEngine(DynamicSpriteFont titleFont, DynamicSpriteFont instructionFont)
        {
            TitleFont = titleFont;
            InstructionFont = instructionFont;
        }

        public override void Update(double dt)
        {
            ref readonly var gameStateEntity = ref ReadEntity<GameStateComponent>();
            ref readonly var gameStateComponent = ref GetComponent<GameStateComponent>(gameStateEntity);

            if (gameStateComponent.GameState == GameState.Title)
            {
                if (Keyboard.GetState().IsKeyDown(Keys.Enter))
                {
                    EndTitle();
                    StartGame();

                    SetComponent(gameStateEntity, new GameStateComponent(GameState.Game));
                }
            }

            if (SomeMessage<ChangeGameStateMessage>())
            {
                ref readonly var changeGameStateMessage = ref ReadMessage<ChangeGameStateMessage>();

                if (changeGameStateMessage.GameState == gameStateComponent.GameState)
                {
                    return;
                }

                if (changeGameStateMessage.GameState == GameState.Title)
                {
                    EndGame();
                    StartTitle();

                    SetComponent(gameStateEntity, new GameStateComponent(GameState.Title));
                }
            }
        }

        private void StartGame()
        {
            ref readonly var playAreaComponent = ref ReadComponent<PlayAreaComponent>();
            var playAreaWidth = playAreaComponent.Width;
            var playAreaHeight = playAreaComponent.Height;

            SendMessage(
                new PaddleSpawnMessage(
                    new MoonTools.Structs.Position2D(20, playAreaHeight / 2 - 40),
                    Enums.PlayerIndex.One,
                    PaddleControl.Player,
                    20,
                    80
                )
            );

            SendMessage(
                new PaddleSpawnMessage(
                    new MoonTools.Structs.Position2D(playAreaWidth - 45, playAreaHeight / 2 - 40),
                    Enums.PlayerIndex.Two,
                    PaddleControl.Computer,
                    20,
                    80
                )
            );

            SendMessage(
                new BallSpawnMessage(
                    new MoonTools.Structs.Position2D(playAreaWidth / 2, playAreaHeight / 2),
                    500,
                    16,
                    16
                ),
                0.5
            );

            // top boundary
            SendMessage(
                new BoundarySpawnMessage(
                    new MoonTools.Structs.Position2D(0, -6),
                    playAreaWidth,
                    6
                )
            );

            // bottom boundary
            SendMessage(
                new BoundarySpawnMessage(
                    new MoonTools.Structs.Position2D(0, playAreaHeight),
                    playAreaWidth,
                    6
                )
            );

            // right boundary
            SendMessage(
                new GoalBoundarySpawnMessage(
                    Enums.PlayerIndex.One,
                    new MoonTools.Structs.Position2D(playAreaWidth, 0),
                    6,
                    playAreaHeight
                )
            );

            // left boundary
            SendMessage(
                new GoalBoundarySpawnMessage(
                    Enums.PlayerIndex.Two,
                    new MoonTools.Structs.Position2D(-6, 0),
                    6,
                    playAreaHeight
                )
            );
        }

        private void EndGame()
        {
            DestroyAllWith<PositionComponent>();
        }

        private void StartTitle()
        {
            ref readonly var playAreaComponent = ref ReadComponent<PlayAreaComponent>();

            var titleDimensions = TitleFont.MeasureString("PongFE");
            var titlePosition = new Position2D(
                (playAreaComponent.Width - titleDimensions.X) / 2,
                (playAreaComponent.Height - titleDimensions.Y) / 4
            );

            SendMessage(new UITextSpawnMessage(
                titlePosition,
                TitleFont,
                "PongFE"
            ));

            var instructionDimensions = InstructionFont.MeasureString("Press Enter to begin");
            var instructionPosition = new Position2D(
                (playAreaComponent.Width - instructionDimensions.X) / 2,
                playAreaComponent.Height * 2 / 3
            );

            SendMessage(new UITextSpawnMessage(
                instructionPosition,
                InstructionFont,
                "Press Enter to play"
            ));
        }

        private void EndTitle()
        {
            DestroyAllWith<UITextComponent>();
        }
    }
}

We have a new method showing up here, DestroyAllWith. This convenient method destroys all Entities that have a component of the given type. When we end gameplay, we destroy everything that has a PositionComponent. When we end the title screen, we destroy everything that has a UITextComponent. Easy.

One last little bit of business to take care of - we have moved the title screen initialization code into this Engine, so let's create an Init game state and then send a message to transition to the Title game state to avoid duplication.

In Enums.cs:

public enum GameState
{
    Init,
    Title,
    Game
}

In PongFEGame:

var ballParametersEntity = WorldBuilder.CreateEntity();
WorldBuilder.SetComponent(ballParametersEntity, new BallParametersComponent(500, 0.5));

var gameStateEntity = WorldBuilder.CreateEntity();
WorldBuilder.SetComponent(gameStateEntity, new GameStateComponent(GameState.Init));

WorldBuilder.SendMessage(new ChangeGameStateMessage(GameState.Title));

And don't forget to add our new Engines and Renderer.

WorldBuilder.AddEngine(new GameStateEngine(ScoreFont, InstructionFont));
WorldBuilder.AddEngine(new GameWinEngine(ScoreFont));
WorldBuilder.AddEngine(new UITextSpawner());

...

WorldBuilder.AddRenderer(new UITextRenderer(SpriteBatch));

That's it... our re-implementation of Pong is complete! If you followed along to this point, give yourself a pat on the back.

17 KiB Raw Permalink Blame History

17 KiB

Raw Permalink Blame History