Pointer Focus Registration Code [work] 【2026 Edition】

By a recovering systems programmer

case WM_MOUSEMOVE: SetFocus(hwnd); You write: pointer focus registration code

PointerFocus::register(target, |focus_state| match focus_state Active => button.highlight(true), Lost => button.highlight(false), ) This eliminates dribble because the framework deduplicates registration across frames. The focus state becomes part of the diff, not a side effect. You write: PointerFocus::register(target

def register_pointer_focus(candidate, event): # 1. Pre-condition: candidate is alive and hittable assert candidate.is_alive() assert candidate.hit_test(event.x, event.y) == True # 2. Invalidate current focus without releasing events yet old_focus = system.pointer_focus system.pointer_focus = None |focus_state| match focus_state Active =&gt