phantomcastle: always convert_alpha

pygame-wasm/phantomcastle/game/scene.py

@@ -34,7 +34,7 @@ class Scene(DrawableGameObject, EventHandler):
         self._surface = pygame.display.set_mode(screen_sz)
         self.surface.fill("white")
         self.rect = self.surface.get_rect()
-        self.background = pygame.image.load(self.assets["bg1k.png"])
+        self.background = pygame.image.load(self.assets["bg1k.png"]).convert_alpha()
         self.background = pygame.transform.scale(self.background, self.rect.size)
 
         double_bg = pygame.Surface((screen_sz.x * 2, screen_sz.y))
@@ -83,7 +83,6 @@ class Scene(DrawableGameObject, EventHandler):
     def draw(self):
         if self.done:
             return
-        self.surface.fill("white")
         self.surface.blit(self.background, (-self.bg_shift, 0))
         if self.level_completed:
             self.end.draw()