One lookup, natural_span, maps a photograph's aspect to the columns its
cell spans, and the same number names its thumbnail class, Wide2, Wide3
or Wide4, 512 pixels of long edge per column, so a 4:1 panorama is as
sharp across four columns as a frame is in one. The boundaries are
where the two neighbouring cells would leave the same share of
themselves undrawn, sqrt(s(s+1)): 2.45 and 3.46, with the first at 1.9
so a 3:2 frame stays a frame. A grid too narrow for the class falls
back to the widest that fits, the tablet gives the whole row, and a
cell asks for the class it is actually drawn at: its span, but never
more than its own class. The merge renders each wide class up to the
composite's own, which covers every fallback.
dtourolle
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