Add project files.

AlientAttack.MonoGame/GameLoops/GameLoop.cs

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+using AlienAttack.MonoGame.Things;
+using AlienAttack.MonoGame.Things.Enemies;
+using AlienAttack.MonoGame.Things.Stars;
+using Microsoft.Xna.Framework;
+using Microsoft.Xna.Framework.Graphics;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace AlienAttack.MonoGame.GameLoops;
+
+internal class GameLoop : GameLoopBase
+{
+    private readonly List<Sprite> _spritesToAdd = [];
+    private readonly Random _random = new();
+
+    private int _spawnNewEnemyThreshold = 100;
+    private float _backgroundYOffset = 0;
+
+    private Starfield _starfield;
+    private Texture2D _pixel;
+
+    protected readonly List<Sprite> Sprites = [];
+
+    public GameLoop(AlienAttackGame game) : base(game)
+    {
+        InitializeStarField(game);
+        Sprites.Add(new Player(game.ViewTransform.ScreenWidth / 2 - 32, game.ViewTransform.ScreenHeight - 64));
+    }
+
+    private void InitializeStarField(AlienAttackGame game)
+    {
+        _starfield = new Starfield(seed: 42);
+
+        //// Far layer: many tiny, slow, faint
+        //_starfield.AddLayer(count: 450, speedPxPerSec: 20f, minSize: 1f, maxSize: 1.5f, minAlpha: 0.15f, maxAlpha: 0.35f);
+
+        //// Mid layer
+        //_starfield.AddLayer(count: 220, speedPxPerSec: 45f, minSize: 1.5f, maxSize: 2.2f, minAlpha: 0.25f, maxAlpha: 0.60f);
+
+        //// Near layer: fewer, bigger, faster, brighter
+        //_starfield.AddLayer(count: 90, speedPxPerSec: 85f, minSize: 2.0f, maxSize: 3.2f, minAlpha: 0.40f, maxAlpha: 0.90f);
+
+        _starfield.AddLayer(count: 450, velocityPxPerSec: new Vector2(+4f, 20f), minSize: 1f, maxSize: 1.5f, minAlpha: 0.15f, maxAlpha: 0.35f);
+        _starfield.AddLayer(count: 220, velocityPxPerSec: new Vector2(-10f, 45f), minSize: 1.5f, maxSize: 2.2f, minAlpha: 0.25f, maxAlpha: 0.60f);
+        _starfield.AddLayer(count: 90, velocityPxPerSec: new Vector2(+20f, 85f), minSize: 2.0f, maxSize: 3.2f, minAlpha: 0.40f, maxAlpha: 0.90f);
+
+
+        _pixel = new Texture2D(game.GraphicsDevice, 1, 1);
+        _pixel.SetData(new[] { Color.White });
+
+        _starfield.Initialize(ViewTransform.ScreenWidth, ViewTransform.ScreenHeight);
+    }
+
+    public override void OnDraw()
+    {
+        _starfield.Draw(SpriteBatch, _pixel);
+        //DrawBackground();
+        DrawSprites();
+    }
+
+    private void DrawBackground()
+    {
+        Texture2D backgroundTexture = Content.Load<Texture2D>($@"Background\PixelBackgroundSeamlessVertically");
+        int blockCountY = (int)Math.Ceiling((decimal)ViewTransform.ScreenHeight / (decimal)backgroundTexture.Height);
+        int blockCountX = (int)Math.Ceiling((decimal)ViewTransform.ScreenWidth / (decimal)backgroundTexture.Width);
+
+        for (int y = 0; y < blockCountY; y++)
+        {
+            float startY = (y * backgroundTexture.Height) + _backgroundYOffset;
+            _backgroundYOffset = _backgroundYOffset + 0.25f;
+
+            if (_backgroundYOffset > ViewTransform.ScreenHeight)
+            {
+                _backgroundYOffset = 0;
+            }
+
+            for (int x = 0; x < blockCountX; x++)
+            {
+                int width = backgroundTexture.Width;
+
+                if (x * backgroundTexture.Width + backgroundTexture.Width > ViewTransform.ScreenWidth)
+                {
+                    width = ViewTransform.ScreenWidth - (x * backgroundTexture.Width);
+                }
+
+                Vector2 position = new(x * backgroundTexture.Width, startY);
+                SpriteBatch.Draw(backgroundTexture, position, new Rectangle(new Point(x, y), new Point(width, backgroundTexture.Height)), Color.White);
+            }
+        }
+    }
+
+    private void DrawSprites()
+    {
+        SpriteDrawArgs args = new(Game);
+
+        foreach (Sprite sprite in Sprites)
+        {
+            sprite.Draw(args);
+        }
+    }
+
+    public override void OnUpdate(GameTime gameTime)
+    {
+        _starfield.Update(gameTime);
+        UpdateSprites(gameTime);
+        CheckSpriteCollisions();
+        ClearDeadSprites();
+        AddEnemySprites();
+        AddNewSprites();
+    }
+
+    private void UpdateSprites(GameTime gameTime)
+    {
+        SpriteUpdateContext args = new(Game)
+        {
+            Random = _random,
+            GameTime = gameTime,
+            SpawnSprite = _spritesToAdd.Add
+        };
+
+        foreach (Sprite sprite in Sprites)
+        {
+            sprite.Update(args);
+        }
+    }
+
+    private void CheckSpriteCollisions()
+    {
+        var collisionSprites = Sprites.Where(x => x.CanCollide).ToList();
+
+        foreach (var sprite in collisionSprites)
+        {
+            foreach (var otherSprite in collisionSprites.Where(x => x != sprite))
+            {
+                SpriteCollisionContext context = new(Game)
+                {
+                    Sprite = otherSprite,
+                    SpawnSprite = _spritesToAdd.Add
+                };
+
+                // TODO: If perfomed once; do not perform again
+                if (sprite.Intersects(otherSprite))
+                {
+                    sprite.OnCollision(context);
+                }
+            }
+        }
+    }
+
+    private void ClearDeadSprites()
+    {
+        var deadSprites = Sprites.Where(x => x.IsDead).ToList();
+
+        foreach (var sprite in deadSprites)
+        {
+            Sprites.Remove(sprite);
+        }
+    }
+
+    private void AddNewSprites()
+    {
+        foreach (Sprite sprite in _spritesToAdd)
+        {
+            Sprites.Add(sprite);
+        }
+
+        _spritesToAdd.Clear();
+    }
+
+    private void AddEnemySprites()
+    {
+        if (_spawnNewEnemyThreshold > 0)
+        {
+            _spawnNewEnemyThreshold--;
+        }
+
+        if (_spawnNewEnemyThreshold == 0)
+        {
+            int randomNumber = _random.Next(0, 100);
+
+            if (randomNumber == 0)
+            {
+                Enemy enemy = new(_random.Next(0, ViewTransform.ScreenWidth - 64), -64);
+                Sprites.Add(enemy);
+                _spawnNewEnemyThreshold = 100 + _random.Next(0, 100);
+            }
+            else if (randomNumber == 1)
+            {
+                RedEnemy enemy = new(_random.Next(0, ViewTransform.ScreenWidth - 64), -64);
+                Sprites.Add(enemy);
+                _spawnNewEnemyThreshold = 100 + _random.Next(0, 100);
+            }
+        }
+    }
+}