The cells were drawn at whatever pixel size the class asked for and the
remainder was left as a bare strip down the right-hand side — up to one
short of a full column of nothing, which on a phone is a quarter of the
screen.
It also had the two quantities depending on each other the wrong way
round. The column count was derived from the fixed cell size, so the two
could disagree about how much room there was and the last column could
start inside the viewport and end outside it.
Solving for the cell removes both at once. Pick how many columns of
roughly the requested size fit — rounded, not floored, because the size
class is a request rather than a measurement and a width nine tenths of
the way to another column should take it — then make those columns share
the width. `columns` cells and the `columns + 1` gaps around them come to
exactly the grid's width, so there is no remainder to strand and nothing
can overhang.
The size class still decides what the user gets, since it is what the
column count is chosen from. It just no longer dictates the pixel, so the
cell flexes a few percent either way to make the row come out even.
dtourolle
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