Function write_segment 

fn write_segment<F>(
    segment_instance_index: Index<BrushSegmentation>,
    frame_state: &mut FrameBuildingState<'_>,
    segments: &mut Storage<BrushSegment>,
    segment_instances: &mut Storage<BrushSegmentation>,
    f: F,
)
where
    F: Fn(&mut GpuBufferWriter<'_, GpuBufferBlockF>),