wumpus-core-0.17.0: Pure Haskell PostScript and SVG generation.

PortabilityGHC with TypeFamilies and more




Data types for stroke and label attributes and type classes for conversion to PostScript's colour and matrix representations.

Wumpus represents pictures as trees - a leaf represents a path or text label. All attributes of a path or text label (colour, stroke width, font, ...) are stored in the leaf. So a picture is a leaf labelled tree.

By contrast, PostScript maintains a graphics state. A PostScript program is free to modify the graphics state anywhere in the program. Stroke width is a general property shared by all elements (initially it has the default value 1). Only stroked paths actually regard stroke width, fonts and filled and clipping paths ignore it. PostScript allows more control over the graphics state by allowing the current state to be saved and restored with the gsave and grestore. This is useful for modularity but is a comparatively expensive procedure.

When Wumpus renders Pictures as PostScript it maintains a limited graphics state with just current colour and current font. This is so Wumpus can avoid repeating setrgbcolor and findfont operations in the generated PostScript if subsequent elements share the same values.


Data types

Stroke attributes

data StrokeAttr Source

Stroke attributes are an algebriac type rather than a record type. This is for convenience when attributing paths - paths can be attibuted with just the differences from the default settings, rather than all the settings whether or not they are important.

data LineCap Source

Line cap - default in output is butt.



data LineJoin Source

Line join - default in output is miter.



data DashPattern Source

Dash pattern - either a solid line or a list of on-off pairs together with an offset into the dashes.


Dash Int [(Int, Int)] 


data FontAttr Source

Font name and size. Equivalent fonts have different names in PostScript and SVG. A PostScript font name includes the font style (e.g. Times-BoldItalic) whereas an SVG font has a name (the font-family attribute) and a style.

For PostScript, the following fonts are expected to exist on most platforms:

 Times-Roman  Times-Italic  Times-Bold  Times-BoldOtalic
 Helvetica  Helvetica-Oblique  Helvetica-Bold  Helvetica-Bold-Oblique
 Courier  Courier-Oblique  Courier-Bold  Courier-Bold-Oblique

See the PostScript Language Reference Manual.

data SVGFontStyle Source

SVG font styles - potentially a style may generate both font-weight and font-style attributes in the SVG output.


Current Translation Matrix

data CTM u Source

PostScript's current transformation matrix.

PostScript and its documentation considers the matrix to be in this form:

 | a  b  0 |
 | c  d  0 | 
 | tx ty 1 |

i.e it considers the homogeneous coordinates of an affine frame as rows rather than columns (Wumpus uses rows, as they were the usual representation in the geometry presentations that inspired it).

Using the component names that we have used in the description of Frame2, the CTM is:

 | e0x  e0y  0 |
 | e1x  e1y  0 | 
 | ox   oy   1 |

The CTM is represented in PostScript as an array, using our names its layout is

 [ e0x e0y e1x e1y ox oy ] 

Some examples, the scaling matrix:

 | sx 0  0 |
 | 0  sy 0 |  = [ sx 0 0 sy 0 0 ]
 | 0  0  1 |

Translation (displacement) :

 | 1  0  0 |
 | 0  1  0 |  = [ 1 0 0 1 tx ty ]
 | tx ty 1 |


 |  cos(a)  sin(a)  0 |
 | -sin(a)  cos(a)  0 |  = [ cos(a) sin(a) -sin(a) cos(a) 0 0 ]
 |    0       0     1 |


CTM !u !u !u !u !u !u 


Eq u => Eq (CTM u) 
Show u => Show (CTM u) 

Convert to CTM

class ToCTM a whereSource

Convert to the CTM. Wumpus offshores affine transformations to PostScript as concat commands. So frames and matrices must support being represented as the CTM.


toCTM :: u ~ DUnit a => a -> CTM uSource


Convert to PSColour

class PSColour a whereSource

Convert to RGB [0,1] for PostScript rendering.


psColour :: a -> RGB3 DoubleSource