--- a/mamba/mutators.py	Sun Sep 11 18:43:21 2011 +0200
+++ b/mamba/mutators.py	Sun Sep 11 18:57:11 2011 +0200
@@ -1,6 +1,9 @@
 """Mutations to apply to images when they're loaded."""
 
 from pygame.transform import rotate
+from pygame.locals import BLEND_ADD, BLEND_MULT
+
+from mamba.data import load_image
 
 
 class Mutator(object):
@@ -18,6 +21,8 @@
     def __eq__(self, other):
         return (self._func is other.func) and self._args == other._args
 
+
+# mutator that does nothing
 NULL = Mutator(lambda x: x)
 
 # sprites mutators
@@ -31,3 +36,25 @@
 BL = Mutator(rotate, -90)
 TR = Mutator(rotate, 90)
 BR = Mutator(rotate, 180)
+
+
+# overlays
+class Overlay(Mutator):
+    """Overlay another image on top of the given one."""
+
+    BLEND = BLEND_ADD
+
+    def __init__(self, filename, blend=None):
+        if blend is None:
+            blend = self.BLEND
+        super(Overlay, self).__init__(self.overlay, blend, filename)
+
+    def overlay(self, image, filename, blend):
+        image = image.copy()
+        overlay = load_image(filename)
+        overlay.blit(image, None, blend)
+        return image
+
+
+class Multiply(Overlay):
+    BLEND = BLEND_MULT