A full-featured rendering backend for diagrams using the cairo rendering engine.

To invoke the cairo backend, you have three options.

• You can use the Diagrams.Backend.Cairo.CmdLine module to create standalone executables which output images when invoked.
• You can use the renderCairo function provided by this module, which gives you more flexible programmatic control over when and how images are output (making it easy to, for example, write a single program that outputs multiple images, or one that outputs images dynamically based on user input, and so on).
• Finally, for the most flexibility, you can directly use methods from the Backend instance for Cairo. In particular, renderDia has the generic type

renderDia :: b -> Options b v n -> QDiagram b v n m -> Result b v n

(omitting a few type class constraints). b represents the backend type, v the vector space, n the numeric field, 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, v ~ V2, and n ~ Double, we have

data family Options Cairo V2 Double = CairoOptions
         { _cairoFileName     :: String             -- ^ The name of the file you want generated
         , _cairoSizeSpec     :: SizeSpec V2 Double -- ^ The requested size of the output
         , _cairoOutputType   :: OutputType         -- ^ the output format and associated options
         , _cairoBypassAdjust :: Bool               -- ^ Should the 'adjustDia' step be bypassed during rendering?
         }

type family Result Cairo V2 Double = (IO (), Render ())

So the type of renderDia resolves to

renderDia :: Cairo -> Options Cairo V2 Double -> QQDiagram Cairo V2 Double Any m -> (IO (), Render ())

which you could call like so:

renderDia Cairo (CairoOptions "foo.png" (Width 250) PNG False) (myDiagram :: QDiagram Cairo V2 Double Any)

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. Note the type annotation on myDiagram which may be necessary to fix the type variable m; this example uses the type synonym Diagram b = QDiagram b (V b) (N b) Any to fix m = Any and fix v and n to backend specific types.

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 V2 Double = CairoOptions
  { _cairoFileName   :: String     -- ^ The name of the file you want generated
  , _cairoSizeSpec   :: SizeSpec V2 Double -- ^ The requested size of the output
  , _cairoOutputType :: OutputType -- ^ the output format and associated options
  , _cairoBypassAdjust  :: Bool    -- ^ Should the 'adjustDia' step be bypassed during rendering?
  }

See the documentation at the top of Diagrams.Backend.Cairo for information on how to make use of this.