[cairo] Pixels Are Not Little Squares

[Lawrence D'Oliveiro]

Another choice quote from Alvy Ray Smith, from 1998
<http://www.alvyray.com/Papers/PapersCG.htm#DigitalMediaConvergence>:

    Symptoms of the ... problem are such expressions as “the edge of the
    pixel” or “the center of the pixel”. This appears in a recent image
    file specification, for example. The problem is often disguised as
    the question of where to place the “centers” of the pixels, on the
    integers or on the half-integers. Although it makes no difference
    where the sampling grid is located, so long as it is consistently
    placed, the sheer existence of this “problem” implies the questioner
    is seeing little squares. ... when thinking properly, one never asks
    about the half-integers. It is like asking should a matrix be
    indexed by integers or half-integers.