Maintainer | diagrams-discuss@googlegroups.com |
---|---|
Safe Haskell | None |
Types which have an intrinsic notion of a "local origin", i.e. things which are not invariant under translation.
Documentation
class VectorSpace (V t) => HasOrigin t whereSource
Class of types which have an intrinsic notion of a "local origin", i.e. things which are not invariant under translation, and which allow the origin to be moved.
One might wonder why not just use Transformable
instead of
having a separate class for HasOrigin
; indeed, for types which
are instances of both we should have the identity
moveOriginTo (origin .^+ v) === translate (negateV v)
The reason is that some things (e.g. vectors, Trail
s) are
transformable but are translationally invariant, i.e. have no
origin.
moveOriginTo :: Point (V t) -> t -> tSource
Move the local origin to another point.
Note that this function is in some sense dual to translate
(for types which are also Transformable
); moving the origin
itself while leaving the object "fixed" is dual to fixing the
origin and translating the diagram.
moveOriginBy :: HasOrigin t => V t -> t -> tSource
Move the local origin by a relative vector.
moveTo :: HasOrigin t => Point (V t) -> t -> tSource
Translate the object by the translation that sends the origin to
the given point. Note that this is dual to moveOriginTo
, i.e. we
should have
moveTo (origin .^+ v) === moveOriginTo (origin .^- v)
For types which are also Transformable
, this is essentially the
same as translate
, i.e.
moveTo (origin .^+ v) === translate v