Build the path for spec between two snapshots. pivot is the resolved
centre for swing when the trajectory names none (the scene centre); without
either, swing turns about the midpoint of the two targets. Every trajectory
but orbit needs perspective at both ends and falls back to orbit otherwise
(and where its own geometry is degenerate).
Build the path for
specbetween two snapshots.pivotis the resolved centre forswingwhen the trajectory names none (the scene centre); without either,swingturns about the midpoint of the two targets. Every trajectory butorbitneeds perspective at both ends and falls back toorbitotherwise (and where its own geometry is degenerate).