Function midpoint 

pub(crate) fn midpoint(a: f32, b: f32) -> f32

The midpoint of a and b.

Deliberately not f32::midpoint: that one avoids overflowing the sum, so it answers a finite midpoint where this answers ±∞. Rect::NOTHING.center() being NaN, and a rect near the top of the range centering at infinity, are the behaviors the render path was built against.