sneak/Shared/ShmupWorld.cs

using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using System;
using System.Collections.Generic;

namespace SemiColinGames {
  public sealed class ShmupWorld : IWorld {
    public class ShmupPlayer {
      public TextureRef Texture = Textures.Yellow2;
      // Center of player sprite.
      public Vector2 Position = new Vector2(48, 1080 / 8);
      // TODO: use a bounds rect instead of HalfSize.
      public Vector2 HalfSize = new Vector2(16, 10);

      private float speed = 150f;
      private float shotCooldown = 0f;

      public void Update(float modelTime, History<Input> input, Rectangle worldBounds,
          ProfilingList<Shot> newShots) {
        // Movement update.
        Vector2 motion = Vector2.Multiply(input[0].Motion, modelTime * speed);
        Position = Vector2.Add(Position, motion);
        Position.X = Math.Max(Position.X, HalfSize.X);
        Position.X = Math.Min(Position.X, worldBounds.Width - HalfSize.X);
        Position.Y = Math.Max(Position.Y, HalfSize.Y);
        Position.Y = Math.Min(Position.Y, worldBounds.Height - HalfSize.Y);

        // Check whether we need to add new shots.
        shotCooldown -= modelTime;
        if (input[0].Attack && shotCooldown <= 0) {
          shotCooldown = 0.2f;
          Vector2 shotOffset = new Vector2(12, 2);
          Vector2 shotPosition = Vector2.Add(Position, shotOffset);
          newShots.Add(new Shot(shotPosition, new Vector2(300, 0)));
        }
      }

      public void Draw(SpriteBatch spriteBatch) {
        Texture2D texture = Texture.Get;
        Vector2 spriteCenter = new Vector2(texture.Width / 2, texture.Height / 2);
        Vector2 drawPos = Vector2.Floor(Vector2.Subtract(Position, spriteCenter));
        spriteBatch.Draw(texture, drawPos, Color.White);
      }
    }

    public class Shot {
      static int color = 0;
      public TextureRef Texture;
      public Vector2 Position;
      public Vector2 HalfSize = new Vector2(11, 4);
      public Rectangle Bounds;
      public Vector2 Velocity;

      public Shot(Vector2 position, Vector2 velocity) {
        Texture = (color % 5) switch {
          0 => Textures.Projectile1,
          1 => Textures.Projectile2,
          2 => Textures.Projectile3,
          3 => Textures.Projectile4,
          _ => Textures.Projectile5
        };
        color++;

        Position = position;
        Velocity = velocity;
        Update(0);  // set Bounds
      }

      public void Update(float modelTime) {
        Position = Vector2.Add(Position, Vector2.Multiply(Velocity, modelTime));
        Bounds = new Rectangle(
            (int) (Position.X - HalfSize.X),
            (int) (Position.Y - HalfSize.Y),
            (int) HalfSize.X * 2,
            (int) HalfSize.Y * 2);
      }

      public void Draw(SpriteBatch spriteBatch) {
        Texture2D texture = Texture.Get;
        Vector2 center = new Vector2(texture.Width / 2, texture.Height / 2);
        spriteBatch.Draw(texture, Vector2.Floor(Vector2.Subtract(Position, center)), Color.White);
      }
    }

    public interface IMoveBehavior {
      public Vector2 Velocity(float modelTime);
    }

    public class MoveLeft : IMoveBehavior {
      public Vector2 Velocity(float modelTime) {
        return new Vector2(-100, 0);
      }
    }

    public class Enemy {
      public TextureRef Texture = Textures.Blue1;
      // Center of sprite.
      public Vector2 Position = new Vector2(1920 / 4 - 48, 1080 / 8);
      // TODO: use a bounds rect instead of HalfSize.
      public Vector2 HalfSize = new Vector2(16, 10);
      public Rectangle Bounds;
      private IMoveBehavior moveBehavior = new MoveLeft();

      public void Update(float modelTime) {
        Vector2 velocity = moveBehavior.Velocity(modelTime);
        Position = Vector2.Add(Position, Vector2.Multiply(velocity, modelTime));

        Bounds = new Rectangle(
            (int) (Position.X - HalfSize.X),
            (int) (Position.Y - HalfSize.Y),
            (int) HalfSize.X * 2,
            (int) HalfSize.Y * 2);
      }

      public void Draw(SpriteBatch spriteBatch) {
        Texture2D texture = Texture.Get;
        Vector2 spriteCenter = new Vector2(texture.Width / 2, texture.Height / 2);
        Vector2 drawPos = Vector2.Floor(Vector2.Subtract(Position, spriteCenter));
        spriteBatch.Draw(texture, drawPos, null, Color.White, 0f,
            spriteCenter, Vector2.One, SpriteEffects.FlipHorizontally, 0f);
      }
    }

    public readonly Rectangle Bounds;
    public readonly ShmupPlayer Player;
    public readonly ProfilingList<Enemy> Enemies;
    public readonly ProfilingList<Shot> Shots;
    private ProfilingList<Shot> newShots;

    public ShmupWorld() {
      Bounds = new Rectangle(0, 0, 1920 / 4, 1080 / 4);
      Player = new ShmupPlayer();
      Enemies = new ProfilingList<Enemy>(100, "enemies");
      Enemies.Add(new Enemy());
      Shots = new ProfilingList<Shot>(100, "shots");
      newShots = new ProfilingList<Shot>(100, "newShots");
    }

    ~ShmupWorld() {
      Dispose();
    }

    public void Dispose() {
      GC.SuppressFinalize(this);
    }

    public void Update(float modelTime, History<Input> input) {
      // Update player, enemies, & shots.
      newShots.Clear();
      Player.Update(modelTime, input, Bounds, newShots);
      foreach (Enemy enemy in Enemies) {
        enemy.Update(modelTime);
      }
      foreach (Shot shot in Shots) {
        shot.Update(modelTime);
      }

      // Add new shots.
      Shots.AddRange(newShots);

      // Reap off-screen objects.
      Rectangle paddedBounds = Bounds;
      paddedBounds.Inflate(16, 16);
      Shots.RemoveAll(shot => !paddedBounds.Intersects(shot.Bounds));
      Enemies.RemoveAll(enemy => !paddedBounds.Intersects(enemy.Bounds));

      Debug.AddToast("shots: " + Shots.Count + " enemies: " + Enemies.Count);
    }
  }
}