shuffel for every frame

src/display.rs

@@ -229,12 +229,13 @@ fn packer_loop(
             continue;
         }
 
-        // Regenerate the permutation when the frame size changes.
+        // Rebuild index array only when frame size changes; otherwise
+        // re-shuffle the existing permutation in place.
         if frame.len() != last_frame_len {
             permutation = (0..frame.len()).collect();
-            fisher_yates_shuffle(&mut permutation, &mut rng);
             last_frame_len = frame.len();
         }
+        fisher_yates_shuffle(&mut permutation, &mut rng);
 
         // Walk the permutation, packing pixels into packets.
         let mut buf = grab_buf(&queue);