Function level_for 

pub fn level_for(texels: (f32, f32), pixels: (f32, f32), deepest: u8) -> u8

The level a quad draws: the deepest whose texels still cover the pixels on both axes. texels is the texel rect fit picked at level 0, pixels the drawn size in physical px (any scale the quad is drawn through multiplied in), deepest the chain’s last level. ⌊log₂ r⌋ for r the smaller of the two ratios, so a bilinear sample inside the level minifies by less than two and a level never magnifies.