Update OnDiskBitmap code to take a filename string with CP7.

CircuitPython_sdcardio_sdioio/show_bitmaps.py

@@ -2,24 +2,35 @@ import os
 import time
 
 import board
-import digitalio
 import displayio
+
 import mount_sd
 
 display = board.DISPLAY
 
 # The bmp files on the sd card will be shown in alphabetical order
-bmpfiles = sorted("/sd/" + filename for filename in os.listdir("/sd")
-    if filename.lower().endswith("bmp"))
+bmpfiles = sorted("/sd/" + fn for fn in os.listdir("/sd") if fn.lower().endswith("bmp"))
 
 while True:
+    if len(bmpfiles) == 0:
+        print("No BMP files found")
+        break
+
     for filename in bmpfiles:
         print("showing", filename)
 
+        # CircuitPython 6 & 7 compatible
         bitmap_file = open(filename, "rb")
         bitmap = displayio.OnDiskBitmap(bitmap_file)
-        tile_grid = displayio.TileGrid(bitmap,
-            pixel_shader=getattr(bitmap, 'pixel_shader', displayio.ColorConverter()))
+        tile_grid = displayio.TileGrid(
+            bitmap,
+            pixel_shader=getattr(bitmap, 'pixel_shader', displayio.ColorConverter())
+        )
+
+        # # CircuitPython 7+ compatible
+        # bitmap = displayio.OnDiskBitmap(filename)
+        # tile_grid = displayio.TileGrid(bitmap, pixel_shader=bitmap.pixel_shader)
+
         group = displayio.Group()
         group.append(tile_grid)
         display.show(group)