True damage vs Shields and such

Since true damage is exactly that, does this also ignore any shields on the champion at the time? So like {{summoner:21}} for example, it states that it "Shields your champion from 115-455 damage (depending on champion level) for 2 seconds.", but is this ignored by true damage? Also what about things like Karmas E or lux's prismatic barrier? Then there is Blitzs passive, is that ignored by true damage when it gets activated?
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