values ▁of ▁the ▁corners ▁of ▁the ▁pixel , ▁use ▁those ▁to ▁calculate ▁the ▁area ▁of ▁the ▁pixel , ▁and ▁figure ▁out ▁how ▁many ▁pixels ▁of ▁exactly ▁the ▁same ▁size ▁would ▁take ▁up ▁the ▁whole ▁texture . ▁ ▁Once ▁this ▁is ▁done ▁the ▁rest ▁becomes ▁easy : ▁perform ▁bil ine ar ▁filtering ▁on ▁the ▁two ▁m ip maps ▁with ▁pixel ▁sizes ▁that ▁are ▁immediately ▁larger ▁and ▁smaller ▁than ▁the ▁calculated ▁size ▁of ▁the ▁pixel , ▁and ▁then ▁interpol ate ▁between ▁them ▁as ▁normal . ▁ ▁Since ▁it ▁uses ▁both ▁larger ▁and ▁smaller ▁m ip maps , ▁tr il ine ar ▁filtering ▁cannot ▁be ▁used ▁in ▁places ▁where ▁the ▁pixel ▁is ▁smaller ▁than ▁a ▁tex el ▁on ▁the ▁original ▁texture , ▁because ▁m ip maps ▁larger ▁than ▁the ▁original ▁texture ▁are ▁not ▁defined . ▁ ▁Bil ine ar ▁filtering ▁still ▁works , ▁and ▁can ▁be ▁used ▁in ▁these ▁situations ▁without ▁worry ing ▁too ▁much ▁about ▁ab rupt ness ▁because ▁bil ine ar ▁and ▁tr il ine ar ▁filtering ▁provide ▁the ▁same ▁result ▁when ▁the ▁pixel ▁size ▁is ▁exactly ▁the ▁same ▁as ▁the ▁size ▁of ▁a ▁tex el ▁on ▁the ▁appropriate ▁m ip map . ▁ ▁Tr il ine ar ▁filtering ▁still ▁has ▁weak ness es , ▁because ▁the ▁pixel ▁is ▁still ▁assumed ▁to ▁take ▁up ▁a ▁square ▁area ▁on ▁the ▁texture . ▁ ▁In ▁particular , ▁when ▁a ▁texture ▁is ▁at ▁a ▁ste ep ▁angle ▁compared ▁to ▁the ▁camera , ▁detail ▁can ▁be ▁lost ▁because ▁the ▁pixel ▁actually ▁takes ▁up ▁a ▁narrow ▁but ▁long ▁tra