Cairo.hs

{-# LANGUAGE TypeFamilies, CPP #-}

-----------------------------------------------------------------------------
-- |
-- Module      :  Diagrams.Backend.Cairo
-- Copyright   :  (c) 2011 Diagrams-cairo team (see LICENSE)
-- License     :  BSD-style (see LICENSE)
-- Maintainer  :  diagrams-discuss@googlegroups.com
--
-- A full-featured rendering backend for diagrams using the
-- cairo rendering engine.
--
-- To invoke the cairo backend, use methods from the
-- 'Diagrams.Core.Types.Backend' instance for @Cairo@.  In particular,
-- 'Diagrams.Core.Types.renderDia' has the generic type
--
-- > renderDia :: b -> Options b v -> QDiagram b v m -> Result b v
--
-- (omitting a few type class constraints).  @b@ represents the
-- backend type, @v@ the vector space, and @m@ the type of monoidal
-- query annotations on the diagram.  'Options' and 'Result' are
-- associated data and type families, respectively, which yield the
-- type of option records and rendering results specific to any
-- particular backend.  For @b ~ Cairo@ and @v ~ R2@, we have
--
-- > data family Options Cairo R2 = CairoOptions
-- >          { cairoFileName     :: String     -- ^ The name of the file you want generated
-- >          , cairoSizeSpec     :: SizeSpec2D -- ^ The requested size of the output
-- >          , cairoOutputType   :: OutputType -- ^ the output format and associated options
-- >          , cairoBypassAdjust :: Bool       -- ^ Should the 'adjustDia' step be bypassed during rendering?
-- >          }
--
-- @
-- data family Render Cairo R2 = C ('RenderM' ())
-- @
--
-- @
-- type family Result Cairo R2 = (IO (), 'Graphics.Rendering.Cairo.Render' ())
-- @
--
-- So the type of 'renderDia' resolves to
--
-- @
-- renderDia :: Cairo -> Options Cairo R2 -> QDiagram Cairo R2 m -> (IO (), 'Graphics.Rendering.Cairo.Render' ())
-- @
--
-- which you could call like @renderDia Cairo (CairoOptions "foo.png"
-- (Width 250) PNG) myDiagram@.  This would return a pair; the first
-- element is an @IO ()@ action which will write out @foo.png@ to
-- disk, and the second is a cairo rendering action which can be used,
-- for example, to directly draw to a Gtk window.
--
-----------------------------------------------------------------------------
module Diagrams.Backend.Cairo

  ( -- * Cairo-supported output formats
    OutputType(..)

    -- * Cairo-specific options
    -- $CairoOptions

-- The below CPP hack is needed because GHC 7.0.x has a bug regarding
-- (re?)export of data family constructors; in particular the below
-- export causes the error "Not in scope: type constructor or class
-- `Options'" even though
-- http://www.haskell.org/haskellwiki/GHC/Type_families#Import_and_export
-- seems to indicate it should be supported.  When using 7.0.x one
-- must import Diagrams.Backend.Cairo.Internal in order to bring
-- CairoOptions into scope.
-- GHC 7.4.0 regression?
#if __GLASGOW_HASKELL__ >= 702 && __GLASGOW_HASKELL__ < 704
  , Options(..)
#endif

    -- * Backend token
  , Cairo(..)
  ) where

import Diagrams.Backend.Cairo.Internal

-- $CairoOptions
--
-- Unfortunately, Haddock does not yet support documentation for
-- associated data families, so we must just provide it manually.
-- This module defines
--
-- > data family Options Cairo R2 = CairoOptions
-- >           { cairoFileName   :: String     -- ^ The name of the file you want generated
-- >           , cairoSizeSpec   :: SizeSpec2D -- ^ The requested size of the output
-- >           , cairoOutputType :: OutputType -- ^ the output format and associated options
-- >           }
--
-- So, for example, you could call the 'renderDia' function (from
-- "Graphics.Rendering.Diagrams.Core") like this:
--
-- > renderDia Cairo (CairoOptions "foo.png" (Width 250) PNG) myDiagram
--
-- /Important note/: a bug in GHC 7.0.x and 7.4.1 prevents
-- re-exporting this data family.  (Strangely, this bug seems to be
-- present in 7.0 and 7.4 but not 7.2.) To bring CairoOptions into
-- scope when using GHC 7.0.x or 7.4 you must import
-- "Diagrams.Backend.Cairo.Internal".