_premultiply_bgra() was iterating over every RGBA pixel in a pure-Python
for-loop at 60 FPS (144x110 sprite = ~950k iterations/sec). This was the
primary cause of UI hangs.
New implementation uses numpy:
- np.frombuffer + reshape to view raw bytes as (H*W, 4) uint8 array
- Fancy-index column reorder [2,1,0,3] for R,G,B,A -> B,G,R,A in one op
- float32 alpha / 255 premultiplication via broadcasting
- tobytes() to emit the final DIB data
Roughly 100x faster than the previous loop, freeing the main thread to
sustain 60 FPS without freezing.
me0nline