fix: improve redraw speed

ui_theme.py

@@ -1,3 +1,5 @@
+from functools import lru_cache
+
 from PIL import Image, ImageColor, ImageDraw
 
 
@@ -26,6 +28,12 @@ COLORS = {
 }
 
 
+@lru_cache(maxsize=4)
+def _load_rgba_source(image_path):
+    """Load and cache a source image in RGBA form for repeated resizes."""
+    return Image.open(image_path).convert("RGBA")
+
+
 def _rgba(color, alpha=255):
     red, green, blue = ImageColor.getrgb(color)
     return red, green, blue, alpha
@@ -187,7 +195,7 @@ def load_cover_background(image_path, width, height, *, overlay_color=None, over
     width = max(1, int(width))
     height = max(1, int(height))
 
-    image = Image.open(image_path).convert("RGBA")
+    image = _load_rgba_source(image_path)
     source_ratio = image.width / image.height
     target_ratio = width / height
 
@@ -198,7 +206,7 @@ def load_cover_background(image_path, width, height, *, overlay_color=None, over
         new_width = width
         new_height = int(width / source_ratio)
 
-    image = image.resize((new_width, new_height), Image.Resampling.LANCZOS)
+    image = image.resize((new_width, new_height), Image.Resampling.BICUBIC)
     left = (new_width - width) // 2
     top = (new_height - height) // 2
     image = image.crop((left, top, left + width, top + height))