{-# LANGUAGE FlexibleInstances , FlexibleContexts #-} ----------------------------------------------------------------------------- -- | -- Module : Graphics.Rendering.Diagrams.HasOrigin -- Copyright : (c) 2011 diagrams-core team (see LICENSE) -- License : BSD-style (see LICENSE) -- Maintainer : diagrams-discuss@googlegroups.com -- -- Types which have an intrinsic notion of a \"local origin\", -- /i.e./ things which are /not/ invariant under translation. -- ----------------------------------------------------------------------------- module Graphics.Rendering.Diagrams.HasOrigin ( HasOrigin(..), moveOriginBy, moveTo ) where import Graphics.Rendering.Diagrams.V import Graphics.Rendering.Diagrams.Points import Data.AffineSpace ((.-^), (.-.)) import Data.VectorSpace -- | 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. class VectorSpace (V t) => HasOrigin t where -- | 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. moveOriginTo :: Point (V t) -> t -> t -- | Move the local origin by a relative vector. moveOriginBy :: HasOrigin t => (V t) -> t -> t moveOriginBy = moveOriginTo . P -- | 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 moveTo :: HasOrigin t => Point (V t) -> t -> t moveTo = moveOriginBy . (origin .-.) instance VectorSpace v => HasOrigin (Point v) where moveOriginTo (P u) p = p .-^ u