Function primitives_for_placement_reusing 

pub fn primitives_for_placement_reusing(
    command: &DrawCommand,
    placement: DrawPlacement,
    size: Size,
    storage: Vec<DrawPrimitive>,
) -> Vec<DrawPrimitive>

primitives_for_placement recording into storage the caller retains between frames. A command that re-records every frame keeps one buffer whose capacity was earned on earlier frames; only the rare marker-bearing recording pays for a second output vector.