Fix texture coordinate parameters.
Fix texture coordinate parameters.

Integer coordinates lie between pixels. Thus, when we sample
the texture, we have to add [0.5, 0.5] to the coordinate.

Yes, Alvy Ray Smith would call us ``half-integerists", and that's
OK because he acknowledges that this approach is
useful for us ``geometry-based computer graphicists" (as he
calls us).

damelang/gezira,damelang/gezira,damelang/gezira