Higher-level widget or animation libraries should probably work in
geom.Pt, but pixels instead of (1/72s of) inches seems a better fit for
lower-level event libraries. Needlessly converting from (float32) pixels
to (float32) points and back can be lossy and lead to off-by-one errors.
Change-Id: I68102e36f2574b07b44c6a1b7281f4f27f9174cf
Reviewed-on: https://go-review.googlesource.com/13002
Reviewed-by: David Crawshaw <crawshaw@golang.org>
