Direction type

src/Diagrams/Angle.hs

@@ -23,16 +23,24 @@ module Diagrams.Angle
        , HasTheta(..)
        ) where
 
-import           Control.Lens            (Iso', Lens', iso, review, (^.))
-                                         -- , review , (^.), _1, _2, Lens', lens)
+import Control.Lens            (Iso', Lens', iso, review, (^.))
 
-import           Data.VectorSpace
+import Data.Monoid      hiding ((<>))
+import Data.Semigroup
+import Data.VectorSpace
 
 -- | Angles can be expressed in a variety of units.  Internally,
 -- they are represented in radians.
 newtype Angle = Radians Double
               deriving (Read, Show, Eq, Ord, Enum, AdditiveGroup)
 
+instance Semigroup Angle where
+    (<>) = (^+^)
+
+instance Monoid Angle where
+    mappend = (<>)
+    mempty = Radians 0
+
 instance VectorSpace Angle where
   type Scalar Angle = Double
   s *^ Radians t = Radians (s*t)

src/Diagrams/Direction.hs

@@ -0,0 +1,54 @@
+{-# LANGUAGE FlexibleContexts           #-}
+{-# LANGUAGE RankNTypes                 #-}
+{-# LANGUAGE TypeFamilies               #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Diagrams.Angle
+-- Copyright   :  (c) 2013 diagrams-lib team (see LICENSE)
+-- License     :  BSD-style (see LICENSE)
+-- Maintainer  :  diagrams-discuss@googlegroups.com
+--
+-- Type for representing directions, polymorphic in vector space
+--
+-----------------------------------------------------------------------------
+
+module Diagrams.Direction
+       ( Direction
+       , _Dir
+       , direction, fromDirection
+       , angleBetweenDirs
+       ) where
+
+import Control.Lens
+import Data.VectorSpace
+
+import Diagrams.Angle
+
+--------------------------------------------------------------------------------
+-- Direction
+
+-- | A vector is described by a @Direction@ and a magnitude.  So we
+-- can think of a @Direction@ as a vector that has forgotten its
+-- magnitude.  @Direction@s can be used with 'fromDirection' and the
+-- lenses provided by its instances.
+data Direction v = Direction v
+
+-- | _Dir is provided to allow efficient implementations of functions
+-- in particular vector-spaces, but should be used with care as it
+-- exposes too much information.
+_Dir :: Iso' (Direction v) v
+_Dir = iso (\(Direction v) -> v) Direction
+
+-- | @direction v@ is the direction in which @v@ points.  Returns an
+--   unspecified value when given the zero vector as input.
+direction :: v -> Direction v
+direction = Direction
+
+-- | @fromDirection d@ is the unit vector in the direction @d@.
+fromDirection :: (InnerSpace v, Floating (Scalar v)) => Direction v -> v
+fromDirection (Direction v) = normalized v
+
+-- | compute the positive angle between the two directions in their common plane
+angleBetweenDirs  :: (InnerSpace v, Scalar v ~ Double) =>
+                     Direction v -> Direction v -> Angle
+angleBetweenDirs d1 d2 = angleBetween (fromDirection d1) (fromDirection d2)

src/Diagrams/Prelude.hs

@@ -88,6 +88,8 @@ module Diagrams.Prelude
        , module Diagrams.Angle
          -- | Convenience infix operators for working with coordinates.
        , module Diagrams.Coordinates
+         -- | Directions, distinguished from angles or vectors
+       , module Diagrams.Direction
 
          -- | A wide range of things (shapes, transformations,
          --   combinators) specific to creating two-dimensional
@@ -132,6 +134,7 @@ import           Diagrams.Combinators
 import           Diagrams.Coordinates
 import           Diagrams.CubicSpline
 import           Diagrams.Deform
+import           Diagrams.Direction
 import           Diagrams.Envelope
 import           Diagrams.Located
 import           Diagrams.Names

src/Diagrams/ThreeD/Camera.hs

@@ -36,6 +36,7 @@ import           Data.Typeable
 
 import           Diagrams.Angle
 import           Diagrams.Core
+import           Diagrams.Direction
 import           Diagrams.ThreeD.Types
 import           Diagrams.ThreeD.Vector
 
@@ -118,13 +119,13 @@ mm50Wide = PerspectiveLens (43.2 @@ deg)  (27 @@ deg)
 -- aspect ratio of 4:3, for VGA and similar computer resulotions.
 mm50Narrow = PerspectiveLens (36 @@ deg) (27 @@ deg)
 
-camForward :: Camera l -> Direction
+camForward :: Camera l -> Direction R3
 camForward = direction . forward
 
-camUp :: Camera l -> Direction
+camUp :: Camera l -> Direction R3
 camUp = direction . up
 
-camRight :: Camera l -> Direction
+camRight :: Camera l -> Direction R3
 camRight c = direction right where
   right = cross3 (forward c) (up c)
 

src/Diagrams/ThreeD/Light.hs

@@ -21,6 +21,7 @@ import           Data.Monoid
 import           Data.Typeable
 
 import           Diagrams.Core
+import           Diagrams.Direction
 import           Diagrams.ThreeD.Types
 
 data PointLight = PointLight P3 (Colour Double)
@@ -48,7 +49,7 @@ pointLight c = mkQD (Prim $ PointLight origin c) mempty mempty mempty
 
 -- | Construct a Diagram with a single ParallelLight, which takes up no space.
 parallelLight :: (Backend b R3, Renderable ParallelLight b)
-                 => Direction -- ^ The direction in which the light travels.
+                 => Direction R3 -- ^ The direction in which the light travels.
                  -> Colour Double -- ^ The color of the light.
                  -> Diagram b R3
 parallelLight d c = mkQD (Prim $ ParallelLight (fromDirection d) c)

src/Diagrams/ThreeD/Transform.hs

@@ -47,6 +47,7 @@ import           Diagrams.Core
 import qualified Diagrams.Core.Transform as T
 
 import           Diagrams.Angle
+import           Diagrams.Direction
 import           Diagrams.Transform
 import           Diagrams.ThreeD.Types
 import           Diagrams.Coordinates
@@ -104,7 +105,7 @@ aboutY ang = fromLinear r (linv r) where
 --   passing through @p@.
 rotationAbout ::
      P3        -- ^ origin of rotation
-  -> Direction -- ^ direction of rotation axis
+  -> Direction R3 -- ^ direction of rotation axis
   -> Angle     -- ^ angle of rotation
   -> T3
 rotationAbout p d a
@@ -127,7 +128,7 @@ rotationAbout p d a
 -- without tilting, it will be, otherwise if only tilting is
 -- necessary, no panning will occur.  The tilt will always be between
 -- ± 1/4 turn.
-pointAt :: Direction -> Direction -> Direction -> T3
+pointAt :: Direction R3 -> Direction R3 -> Direction R3 -> T3
 pointAt a i f = pointAt' (fromDirection a) (fromDirection i) (fromDirection f)
 
 -- | pointAt' has the same behavior as 'pointAt', but takes vectors

src/Diagrams/ThreeD/Types.hs

@@ -1,5 +1,4 @@
 {-# LANGUAGE FlexibleInstances          #-}
-{-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE MultiParamTypeClasses      #-}
 {-# LANGUAGE RankNTypes                 #-}
 {-# LANGUAGE TypeFamilies               #-}
@@ -26,8 +25,6 @@ module Diagrams.ThreeD.Types
        , T3
        , r3Iso, p3Iso
 
-         -- * Directions in 3D
-       , Direction, direction, fromDirection, angleBetweenDirs
        -- * other coördinate systems
        , Spherical(..), Cylindrical(..), HasPhi(..)
        ) where
@@ -37,6 +34,7 @@ import           Control.Lens           (Iso', Lens', iso, over
 
 import           Diagrams.Core
 import           Diagrams.Angle
+import           Diagrams.Direction
 import           Diagrams.TwoD.Types    (R2)
 import           Diagrams.Coordinates
 
@@ -122,18 +120,6 @@ instance Transformable R3 where
 instance HasCross3 R3 where
   cross3 u v = r3 $ cross3 (unr3 u) (unr3 v)
 
---------------------------------------------------------------------------------
--- Direction
-
--- | A @Direction@ represents directions in R3.  The constructor is
--- not exported; @Direction@s can be used with 'fromDirection' and the
--- lenses provided by its instances.
-data Direction = Direction R3
-
--- | Not exported
-_Dir :: Iso' Direction R3
-_Dir = iso (\(Direction v) -> v) Direction
-
 instance HasX R3 where
     _x = r3Iso . _1
 
@@ -203,21 +189,8 @@ instance Cylindrical P3 where
 instance Spherical P3 where
     spherical = _relative origin . spherical
 
-instance HasTheta Direction where
+instance HasTheta (Direction R3) where
     _theta = _Dir . _theta
 
-instance HasPhi Direction where
+instance HasPhi (Direction R3) where
     _phi = _Dir . _phi
-
--- | @direction v@ is the direction in which @v@ points.  Returns an
---   unspecified value when given the zero vector as input.
-direction :: R3 -> Direction
-direction = Direction
-
--- | @fromDirection d@ is the unit vector in the direction @d@.
-fromDirection :: Direction -> R3
-fromDirection (Direction v) = normalized v
-
--- | compute the positive angle between the two directions in their common plane
-angleBetweenDirs  :: Direction -> Direction -> Angle
-angleBetweenDirs d1 d2 = angleBetween (fromDirection d1) (fromDirection d2)

src/Diagrams/TwoD.hs

@@ -65,7 +65,6 @@ module Diagrams.TwoD
        , P2, p2, unp2, mkP2
        , T2
        , unitX, unitY, unit_X, unit_Y
-       , direction, fromDirection
 
          -- * Angles
        , tau
@@ -200,7 +199,7 @@ module Diagrams.TwoD
 
          -- * Combinators
          -- ** Combining multiple diagrams
-       , (===), (|||), atAngle
+       , (===), (|||), atDirection
        , hcat, hcat'
        , vcat, vcat'