Add a transformation matrix to spriteBatch.Draw().

Instead of having every drawable object know how to transform itself based on
the camera position, we pass in a transformation matrix to spriteBatch.Draw().
Unfortunately MonoGame only lets us specify a translation that works over an
entire SpriteBatch.Begin() call, so we need to begin & end separately for
objects that *aren't* supposed to translate at the same rate as the camera.

Fixes #39.

GitOrigin-RevId: afab72c39236b1b46fe1597412209981ddae9c7c

Shared/Camera.cs

@@ -10,6 +10,7 @@ namespace SemiColinGames {
     public int Width { get => bbox.Width; }
     public int Height { get => bbox.Height; }
     public int Left { get => bbox.Left; }
+    public int Top { get => bbox.Top; }
 
     public void Update(Point player, int worldWidth) {
       int diff = player.X - bbox.Center.X;

Shared/Debug.cs

@@ -98,13 +98,12 @@ namespace SemiColinGames {
       }
     }
 
-    public static void Draw(SpriteBatch spriteBatch, Camera camera) {
+    public static void Draw(SpriteBatch spriteBatch) {
       if (!Enabled) {
         return;
       }
       foreach (var debugRect in rects) {
         var rect = debugRect.Rect;
-        rect.Offset(-camera.Left, 0);
         var color = debugRect.Color;
         // top side
         spriteBatch.Draw(
@@ -123,7 +122,7 @@ namespace SemiColinGames {
         Point[] points = Line.Rasterize(line.Start, line.End);
         foreach (var point in points) {
           spriteBatch.Draw(
-            whiteTexture, new Rectangle(point.X - camera.Left, point.Y, 1, 1), line.Color);
+            whiteTexture, new Rectangle(point.X, point.Y, 1, 1), line.Color);
         }
       }
     }

Shared/Player.cs

@@ -294,14 +294,13 @@ namespace SemiColinGames {
       }
     }
 
-    public void Draw(SpriteBatch spriteBatch, Camera camera) {
+    public void Draw(SpriteBatch spriteBatch) {
       int index = SpriteIndex(pose);
       Rectangle textureSource = new Rectangle(index * spriteWidth, 0, spriteWidth, spriteHeight);
       Vector2 spriteCenter = new Vector2(spriteWidth / 2, spriteHeight / 2 + spriteCenterYOffset);
       SpriteEffects effect = facing == Facing.Right ?
         SpriteEffects.FlipHorizontally : SpriteEffects.None;
-      Vector2 drawPos = new Vector2(position.X - camera.Left, position.Y);
-      spriteBatch.Draw(texture, drawPos, textureSource, Color.White, 0f, spriteCenter,
+      spriteBatch.Draw(texture, position.ToVector2(), textureSource, Color.White, 0f, spriteCenter,
         Vector2.One, effect, 0f);
     }
   }

Shared/SneakGame.cs

@@ -144,15 +144,20 @@ namespace SemiColinGames {
       bgSource = new Rectangle(
         (int) (camera.Left * 0.5), 0, camera.Width, camera.Height);
       spriteBatch.Draw(grasslandBg1, bgTarget, bgSource, Color.White);
+      spriteBatch.End();
+
+      // Set up transformation matrix for drawing world objects.
+      Matrix transform = Matrix.CreateTranslation(-camera.Left, -camera.Top, 0);
+      spriteBatch.Begin(SpriteSortMode.Deferred, null, SamplerState.LinearWrap, null, null, null, transform);
 
       // Draw player.
-      player.Draw(spriteBatch, camera);
+      player.Draw(spriteBatch);
 
       // Draw foreground tiles.
-      world.Draw(spriteBatch, camera);
+      world.Draw(spriteBatch);
 
       // Draw debug rects & lines.
-      Debug.Draw(spriteBatch, camera);
+      Debug.Draw(spriteBatch);
 
       // Aaaaand we're done.
       spriteBatch.End();

Shared/World.cs

@@ -42,9 +42,8 @@ namespace SemiColinGames {
     public Rectangle Position { get; private set; }
     public Terrain Terrain { get; private set; }
 
-    public void Draw(SpriteBatch spriteBatch, Camera camera) {
-      Vector2 drawPos = new Vector2(Position.Left - camera.Left, Position.Top);
-      spriteBatch.Draw(texture, drawPos, textureSource, Color.White);
+    public void Draw(SpriteBatch spriteBatch) {
+      spriteBatch.Draw(texture, Position.Location.ToVector2(), textureSource, Color.White);
     }
 
     private Rectangle TextureSource() {
@@ -125,9 +124,9 @@ namespace SemiColinGames {
           new Vector2(Width + 1, 0), new Vector2(1, float.MaxValue));
     }
 
-    public void Draw(SpriteBatch spriteBatch, Camera camera) {
+    public void Draw(SpriteBatch spriteBatch) {
       foreach (Tile t in tiles) {
-        t.Draw(spriteBatch, camera);
+        t.Draw(spriteBatch);
       }
     }