--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gamelib/imagecache.py	Mon Aug 31 16:47:54 2009 +0000
@@ -0,0 +1,72 @@
+"""Central image cache to avoid loading images multiple times."""
+
+import pygame
+import data
+
+class ImageCache(object):
+    """Create an image cache with a list of modifiers."""
+
+    def __init__(self):
+        # (image name, ordered modifiers tuple) -> pygame surface
+        self._cache = {}
+        self._modifiers = {}
+
+    def register_modifier(self, name, function):
+        """Register a post-load modifying function."""
+        if name in self._modifiers:
+            raise ValueError("Attempt to re-register and existing modifier function.")
+        self._modifiers[name] = function
+
+    def load_image(self, name, modifiers=None):
+        """Load an image from disk or return a cached image.
+
+           name: image name relative to data path.
+           modifers: ordered list of modifiers to apply.
+           """
+        # convert lists to tuples
+        if modifiers is not None:
+            modifiers = tuple(modifiers)
+
+        # convert empty tuples to None
+        if not modifiers:
+            modifiers = None
+
+        # look for modified image
+        key = (name, modifiers)
+        if key in self._cache:
+            return self._cache[key]
+
+        # look for unmodified image
+        base_key = (name, None)
+        if base_key in self._cache:
+            image = self._cache[base_key]
+        else:
+            image = pygame.image.load(data.filepath(name))
+            self._cache[base_key] = image
+
+        # handle unmodified case
+        if modifiers is None:
+            return image
+
+        for mod in modifiers:
+            image = self._modifiers[mod](image)
+
+        self._cache[key] = image
+        return image
+
+# modifiers
+
+from pygame.locals import BLEND_RGBA_MULT
+NIGHT_COLOUR = (100.0, 100.0, 200.0, 255.0)
+
+def convert_to_night(image):
+    """Convert a day tile to a night tile."""
+    night_image = image.copy()
+    night_image.fill(NIGHT_COLOUR, None, BLEND_RGBA_MULT)
+    return night_image
+
+# globals
+
+cache = ImageCache()
+cache.register_modifier("night", convert_to_night)
+load_image = cache.load_image