Function round_layout_to_grid 

pub fn round_layout_to_grid(
    tree: &mut impl RoundTree,
    node_id: NodeId,
    steps_per_unit: f32,
)

round_layout onto a grid of steps_per_unit steps per unit instead of whole units: with layout in logical pixels and steps_per_unit the display’s device pixels per logical pixel, every edge lands on a device pixel, at fractional scales (1.5) as at whole ones. A scale that is not a finite positive number rounds to whole units. (Tilo patch: see vendor/taffy/TILO-PATCH.md.)