Chọn face
Chia face
extrude
f Từ khung thành face
outside - inside
CTRL-N. Calculate Normals Outside. All normals from selected faces are recalculated and consistently set in the same direction. An attempt is made to direct all normals ‘outward’.
SHIFT-CTRL-N. Calculate Normals Inside. All normals from selected faces are recalculated and consistently set in the same direction. An attempt is made to direct all normals ‘inward’.