scroll y by a constant scale instead of per-layer.

Shared/Scene.cs

@@ -74,14 +74,16 @@ namespace SemiColinGames {
       spriteBatch.Begin(SpriteSortMode.Deferred, null, SamplerState.LinearWrap, null, null);
       Rectangle bgTarget = new Rectangle(0, 0, camera.Width, camera.Height);
 
-      float bgScale = 1f / 16;
+      float xScale = 1f / 16;  // Changes with each layer (the layers further back scroll less).
+      float yScale = 1f / 4;  // Constant across all layers.
       for (int i = 0; i < Textures.Backgrounds.Length; i++) {
-        float yDiff = (world.Height - camera.Bottom) * bgScale;
-        float yOffset = Textures.Backgrounds[i].Get.Height - camera.Height - yDiff;
+        Texture2D background = Textures.Backgrounds[i].Get;
+        float yDiff = (world.Height - camera.Bottom) * yScale;
+        float yOffset = background.Height - camera.Height - yDiff;
         Rectangle bgSource = new Rectangle(
-          (int) (camera.Left * bgScale), (int) yOffset, camera.Width, camera.Height);
-        spriteBatch.Draw(Textures.Backgrounds[i].Get, bgTarget, bgSource, Color.White);
-        bgScale *= 2;
+            (int) (camera.Left * xScale), (int) yOffset, camera.Width, camera.Height);
+        spriteBatch.Draw(background, bgTarget, bgSource, Color.White);
+        xScale *= 2;
       }
       spriteBatch.End();