Recache on file updates

Unfortunately, packed images don't appear to store any kind of modify
time attribute. In the case of those, we're just idly hoping that we can
find one on disk.

korman/exporter/image.py

@@ -16,6 +16,7 @@
 import enum
 from pathlib import Path
 from PyHSPlasma import *
+import time
 import weakref
 
 _HEADER_MAGICK = b"KTH\x00"
@@ -44,6 +45,7 @@ class _EntryBits(enum.IntEnum):
     compression = 3
     source_size = 4
     export_size = 5
+    last_export = 6
 
 
 class _CachedImage:
@@ -55,6 +57,8 @@ class _CachedImage:
         self.source_size = None
         self.export_size = None
         self.compression = None
+        self.export_time = None
+        self.modify_time = None
 
     def __str__(self):
         return self.name
@@ -127,6 +131,19 @@ class ImageCache:
         if tuple(bl_image.size) != cached_image.source_size:
             return None
 
+        # if the image is on the disk, we can check the its modify time for changes
+        if cached_image.modify_time is None:
+            # if the image is packed, the filepath will be some garbage beginning with
+            # the string "//". There isn't much we can do with that, unless the user
+            # happens to have an unpacked copy lying around somewheres...
+            path = Path(bl_image.filepath_from_user())
+            if path.is_file():
+                cached_image.modify_time = path.stat().st_mtime
+                if cached_image.export_time and cached_image.export_time < cached_image.modify_time:
+                    return None
+            else:
+                cached_image.modify_time = 0
+
         # ensure the data has been loaded from the cache
         if cached_image.image_data is None:
             try:
@@ -231,6 +248,8 @@ class ImageCache:
             image.source_size = (stream.readInt(), stream.readInt())
         if flags[_EntryBits.export_size]:
             image.export_size = (stream.readInt(), stream.readInt())
+        if flags[_EntryBits.last_export]:
+            image.export_time = stream.readDouble()
 
         # do we need to check for duplicate images?
         self._images[(image.name, image.compression)] = image
@@ -307,6 +326,7 @@ class ImageCache:
         flags[_EntryBits.compression] = True
         flags[_EntryBits.source_size] = True
         flags[_EntryBits.export_size] = True
+        flags[_EntryBits.last_export] = True
 
         stream.write(_ENTRY_MAGICK)
         flags.write(stream)
@@ -318,3 +338,4 @@ class ImageCache:
         stream.writeInt(image.source_size[1])
         stream.writeInt(image.export_size[0])
         stream.writeInt(image.export_size[1])
+        stream.writeDouble(time.time())