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Diagrams

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The diagrams library provides an embedded domain-specific language (EDSL) for creating simple pictures and diagrams in Haskell


Contents

1 Rewrite

1.1 Core DSL

1.1.1 Style

Do we either want

yellowCircle x y radius = yellowFill $ circleShape x y radius

or

drawYellowCircle x y radius = do $

   setFill yellow
   drawCircle x y radius

?

The first version allows better reuse and functional composition.

1.1.2 Elements

  • graphical primitives
    • path
      • boundingBox
      • moveTo, lineTo, cubic bezier, quadratic bezier, arcTo
    • text
      • boundingBox
      • convertToPath
    • circle
      • boundingBox
      • convertToPath
    • ellipse
      • boundingBox
      • convertToPath
    • rectangle
      • boundingBox
      • convertToPath
    • polygon
      • boundingBox
      • convertToPath
    • polyline
      • boundingBox
      • convertToPath
  • graphical attributes
    • fill
      • paint
        • solid color, gradient, pattern
      • fill rule
        • evenOdd, nonZero
    • stroke
      • paint
        • solid color, gradient, pattern
      • width
      • line cap
      • line join
      • miter limit
      • dash
        • offset
        • array
    • marker symbols
    • effects
      • shadow, blur, turbulence
  • constraint solving
  • animations/pages/frames

1.2 Data structures

data Figure = Figure {
    fill :: Fill
  , shape :: Shape
  , stroke :: Stroke
  }
 
data Fill = Fill {
    fillPaint :: Paint,
  }
 
data Stroke = Stroke {
    strokePaint :: Paint,
  , lineWidth :: Double,
  , dashPattern :: DashPattern
  , lineCap :: LineCap
  , lineJoin :: LineJoin
  , miterLimit :: Double
  } deriving(Eq, Show)
 
data Paint =
    SolidColor
  | Pattern
  | Gradient
  deriving(Eq, Show)
 
data LineCap =
    LineCapButt
  | LineCapRound
  | LineCapSquare
  deriving(Eq, Show)
 
data LineJoin =
    LineJoinMiter
  | LineJoinRound
  | LineJoinBevel
  deriving(Eq, Show)
 
data Shape =
    Path
  | Primitive
  | Text
  deriving(Eq, Show)
 
data Path = Path {
    segments :: [Segment]
  }
  deriving(Eq, Show)
 
data Segment = 
    Move Point
  | Line {
      a :: Point
    , b :: Point
    }
  | HorizontalLine {
      a :: Point
    , w :: Double
    }
  | VerticalLine {
      a :: Point
    , h :: Double
    }
  | QuadraticBezier Point Point Point
  | CubicBezier Point Point Point Point
  deriving(Eq, Show)
 
data Point =
    Node2d Double Double
  | Node3d Double Double Double
  deriving(Eq, Show)
 
data Primitive =
    Circle
  | Ellipse
  | Rectangle
  | RegularPolygon
  | Square
  | Star
  deriving(Eq, Show)
 
class PathLike a =
	convertToPath :: a -> Path


1.3 Modules/Extensions

1.3.1 Paths

  • inset, outset
  • boolean operations
  • morphing
  • approximation (autotrace)

See

1.3.2 Shapes and symbols

1.4 Input/Output

Many Haskell graphic libraries are tied to a specific rendering backend (Cairo, OpenGL, libGD etc) which makes collaboration and reuse of code and data structures very hard or impossible.

Also some dependencies are hard to fulfill. Cairo is very difficult to install on Mac OS 10.6. If you just need to generate PDF diagrams, you could choose the pure HPDF library where e.g. Hieroglyph can not be installed because of its Cairo dependence.

1.4.1 Output

  • interactive drawing via Cairo
  • PDF export via pure HPDF
  • EPS export
  • SWF export
  • LaTeX export
  • exotic backends

1.4.2 Input

  • pure Haskell PNG import via pngload
  • pure Haskell SVG import

2 Inspiration

2.1 Related non-Haskell projects

2.2 Food for thought