A build's sampled image elements often repeat the element just before them
in plan order (the same eight descriptor words). Each still took its own
stage-A record (decode, collect, DCC key read, cache entry) and its own
stage-B lookup.
The lookups run in plan order and nothing runs between two consecutive ones,
so a repeated element's lookup would find the state the previous lookup just
left: the entry it validated or made, current against the same collect. Such
an element now binds the previous element's texture (when the depth-compare
flag matches too, which is part of the cache key), and stage A gives it a
record of the decoded descriptor only. An element repeating an earlier but
not the immediately preceding one still takes its own lookup, as does any
element after a storage image lookup.
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