nem0

// only handles coplexity on top level, if you have a node with 1M children, you are out of luck
// changes in clipped parts are not detected, so if somebody deleted nodes in clipped, scrollbar is not updated until user actually scrolls
// scrolling and changes refresh the clipper == that part is as slow as no clipping at all
// only single list in BeginChild/EndChild is tested
struct TreeViewClipper {
	// persist
	float cursor_end = 0;
	float cursor_visible_start = 0;
	uint first_visible_index = 0;
	float last_scroll = 0;