▁door way ▁of ▁a ▁small ▁building ▁could ▁lead ▁into ▁a ▁network ▁of ▁rooms ▁larger ▁than ▁the ▁building ▁itself ). ▁While ▁all ▁these ▁made ▁the ▁games ▁using ▁the ▁engine ▁appear ▁to ▁be ▁ 3 D , ▁it ▁wouldn ' t ▁be ▁until ▁later ▁first - person ▁shoot ers , ▁such ▁as ▁Qu ake , ▁which ▁used ▁the ▁Qu ake ▁engine , ▁that ▁the ▁engine ▁actually ▁stored ▁the ▁world ▁geometry ▁as ▁true ▁ 3 D ▁information , ▁making ▁the ▁creation ▁of ▁one ▁area ▁stack ed ▁at op ▁another ▁area ▁in ▁a ▁single ▁map ▁very ▁feas ible . ▁ ▁V ox els ▁ ▁Later ▁versions ▁of ▁Ken ▁Silver man ' s ▁Build ▁engine ▁allowed ▁game ▁selected ▁art ▁t iles ▁to ▁be ▁replaced ▁by ▁ 3 D ▁objects ▁made ▁of ▁vo x els . ▁This ▁feature ▁appeared ▁too ▁late ▁to ▁be ▁used ▁in ▁Duke ▁N uk em ▁ 3 D , ▁but ▁was ▁seen ▁in ▁some ▁of ▁the ▁later ▁Build ▁engine ▁games . ▁Blood ▁uses ▁vo x els ▁for ▁weapon ▁and ▁am mo ▁pick ups , ▁power - ups , ▁and ▁eye - c andy ▁( such ▁as ▁the ▁tomb st ones ▁in ▁the ▁" C rad le ▁to ▁Gra ve " ▁level , ▁some ▁ch airs , ▁and ▁a ▁cry stal ▁ball ▁in ▁" D ark ▁Car n ival "). ▁Sh adow ▁War rior ▁makes ▁even ▁more ▁advanced ▁use ▁of ▁the ▁technology , ▁with ▁vo x els ▁that ▁can ▁be ▁placed ▁on ▁walls ▁( all ▁of ▁the ▁game ' s ▁switch es ▁and ▁buttons ▁are ▁vo