```{-# LANGUAGE FlexibleContexts
, TypeFamilies
#-}
-----------------------------------------------------------------------------
-- |
-- Module      :  Diagrams.TwoD.Size
-- Copyright   :  (c) 2011 diagrams-lib team (see LICENSE)
-- Maintainer  :  diagrams-discuss@googlegroups.com
--
-- Utilities for working with sizes of two-dimensional objects.
--
-----------------------------------------------------------------------------
module Diagrams.TwoD.Size
(
-- * Size and extent of diagrams in R2
-- ** Computing sizes
width, height, size2D
, extentX, extentY, center2D

-- ** Specifying sizes
, SizeSpec2D(..)
) where

import Graphics.Rendering.Diagrams
import Diagrams.TwoD.Types

import Control.Arrow ((***), (&&&))

------------------------------------------------------------
-- Computing diagram sizes
------------------------------------------------------------

-- | Compute the width of a boundable object.
width :: (Boundable a, V a ~ R2) => a -> Double
width = negate . uncurry (-) . extentX

-- | Compute the height of a boundable object.
height :: (Boundable a, V a ~ R2) => a -> Double
height = negate . uncurry (-) . extentY

-- | Compute the width and height of a boundable object.
size2D :: (Boundable a, V a ~ R2) => a -> (Double, Double)
size2D = width &&& height

-- | Compute the absolute x-coordinate range of a boundable object in
--   R2, in the form (lo,hi).
extentX :: (Boundable a, V a ~ R2) => a -> (Double, Double)
extentX d = (-f (-1,0), f (1,0))
where f = appBounds \$ getBounds d

-- | Compute the absolute y-coordinate range of a boundable object in
--   R2, in the form (lo,hi).
extentY :: (Boundable a, V a ~ R2) => a -> (Double, Double)
extentY d = (-f (0,-1), f (0,1))
where f = appBounds \$ getBounds d

-- | Compute the point at the center (in the x- and y-directions) of a
--   boundable object.
center2D :: (Boundable a, V a ~ R2) => a -> P2
center2D = P . (mid *** mid) . (extentX &&& extentY)
where mid = (/2) . uncurry (+)

------------------------------------------------------------
-- Size specifications
------------------------------------------------------------

-- | A specification of a (requested) rectangular size.
data SizeSpec2D = Width  Double       -- ^ Specify an explicit
-- width. The height should be
-- determined automatically (so
-- as to preserve aspect ratio).
| Height Double       -- ^ Specify an explicit
-- height. The width should be
-- determined automatically (so
-- as to preserve aspect ratio)
| Dims Double Double  -- ^ An explicit specification
--   of both dimensions.
| Absolute            -- ^ Absolute size: use whatever
-- size an object already has;
-- do not rescale.
```