Can someone please help clarify the block unlocker algorithm and who gets rewards?

[CerveloFellow]

Is anyone able to clarify what the algorithm is for distributing rewards? Is it shares per block solved? So only the people who've contributed to solving the block that was won earn a piece of the reward? Or is since last block, where anyone who's contributed shares since the last block was solved would earn a piece of the reward? Something different? If a person puts a lot of hashing power in to a small pool that may only unlock a block a week or something, but is offline when the block is solved, would they get any reward?

Thanks.