add basic Enemy skeleton

Shared/ShmupScene.cs

@@ -45,7 +45,11 @@ namespace SemiColinGames {
           SamplerState.PointClamp, DepthStencilState.Default,
           RasterizerState.CullNone);
 
-      // Draw player, then shots.
+      // Draw enemies, then player, then shots.
+      foreach (ShmupWorld.Enemy e in world.Enemies) {
+        e.Draw(spriteBatch);
+      }
+
       world.Player.Draw(spriteBatch);
 
       foreach (ShmupWorld.Shot s in world.Shots) {

Shared/ShmupWorld.cs

@@ -53,6 +53,7 @@ namespace SemiColinGames {
       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,
@@ -84,13 +85,35 @@ namespace SemiColinGames {
       }
     }
 
+    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 void Update(float modelTime) {
+      }
+
+      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;
 
     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");
     }
 
@@ -103,8 +126,11 @@ namespace SemiColinGames {
     }
 
     public void Update(float modelTime, History<Input> input) {
-      // Update player & shots.
+      // Update player, enemies, & shots.
       ProfilingList<Shot> newPlayerShots = Player.Update(modelTime, input, Bounds);
+      foreach (Enemy enemy in Enemies) {
+        enemy.Update(modelTime);
+      }
       foreach (Shot shot in Shots) {
         shot.Update(modelTime);
       }