wumpus-core: Pure Haskell PostScript and SVG generation.

Wumpus-Core is a low-level library for generating static 2D vector pictures, its salient feature is portability due to no FFI dependencies. It can generate PostScript (EPS) files and SVG files. The generated PostScript code is plain and reasonably efficient as the use of stack operations, i.e gsave and grestore, is minimized.

Although Wumpus-Core only generates vector output, the generated PostScript can be interpreted by GraphicsMagick or a similar tool to convert EPS files into bitmap image files (e.g JPEGs).

Wumpus-Core makes pictures from paths and text labels. Paths themselves are made from points. The usual affine transformations (rotations, scaling, translations) can be applied to Pictures. Unlike PostScript there is no notion of a current point, Wumpus-Core builds pictures in a coordinate-free style.

GENERAL DRAWBACKS...

For actually building pictures, diagrams, etc. Wumpus-Core is very low-level. There is a supplementary package Wumpus-Basic available that helps create certain types of diagram, but it is experimental - functionality is added and dropped between releases, it has no stable API.

Some of the design decisions made for Wumpus-Core are not sophisticated (e.g. how path and text attributes like colour are handled, and how the bounding boxes of text labels are calculated), so Wumpus might be limited compared to other systems. However, the design permits a fairly simple implementation, which is a priority.

UPDATING from 0.37.0 or earlier to 0.41.0.

There were substantial changes in verion 0.40.0 - hence the version number jump from 0.37.0. Version 0.41.0 introduces mostly cosmetic changes, but for upgrading from 0.37.0 or earlier the change-notes that follow are still relevant.

Core.Picture API change - the path construction function has changed from path to primPath. The type of the path segments has changed, the functions lineTo and curveTo now build AbsPathSegments and primPath consumes AbsPathSegments.

The Text API has changed substantially, however most user code should only need minor changes. The functions writePS_latin1, writeEPS_latin1 and writeSVG_latin1 have been removed, code should be changed to use writePS, writeEPS and and writeSVG respectively. These three functions no longer take a TextEncoder argument as TextEncoders no longer exist.

The Font Size API has also changed substantially. It now exports a more consistent set of metrics (consistent with what is present in font files - the previous version was derived from hand measurements). It also adds a margin to bounding box calculations, again this is more consistent with how font files actually work.

The handling of escaped special characters is now more consistent and the escaping mecahnism has been clarified (previously the documentation and the implementation were at odds): PostScript glyph names are delimited between & (ampersand) and ; (semi), Unicode code points are delimited by &# (ampersand-hash) and ; (semi). Note Wumpus silently drops mal-formed escape charcters, for robustness this is preferable to throwing a runtime error, but it does mean the output needs visually checking.

Changelog:

v0.40.0 to v0.41.0:

• Changed PostScript output to use pre-defined procedures for circles and ellipses. This should be a significant optimization for drawings that have many circles or ellipses. For drawings that do not use circles or ellipses, it adds circa. 75 lines to the generated PostScript which is tolerable.

• API change - Core.Text.Base no longer exports the constructor and field label for EscapedText, it is now an opaque type. For a building EscapedText either the existing safeconstructor escapeString or the new function wrapEscChar should be used. For destructing EscapedText there is a new function destrEscapedText.

• API change - the argument order of the functions rtextlabel and rescapedlabel in Core.Picture has changed. The order of angle of rotation and the baseline-left has been swapped so that angle of rotation is first. This matches the other rotated graphics in Core.Picture.

• Upper bounds of Cabal build depends relaxed a bit.

• Added the UNil type to Core.Geometry and added affine instances for the UNil type, plus Maybe and Pair. UNil is useful for higher-level drawing (it is used extensively in Wumpus-Basic).

• Added the function emptyPath to Core.Picture. This creates a null path with an empty list of path segments. Null paths still need a start point - this is minimum needed for bounding box calculation. Improved the PostScript and SVG output so there is no code generated for empty paths and textlabels.

• Added vectorPath to Core.Picture.

• Added boundaryCenter to Core.BoundingBox.

• Improved generated SVG code generation for ellipses / circles.

v0.37.0 to v0.40.0:

• Text handling substantially revised. SVG text output is now better aligned to Unicode. The encoding tables for PostScript have been re-thought, the previous implementation had some serious design flaws that should now be rectified.

• The rules for escaping special characters has been clarified. Previously the documentation suggested ampersand-name-semicolon could be used to escape glyph names however only ampersand-hash-name-semicolon worked. ampersand-name-semicolon is now the correct way. The ampersand-hash prefix is for numeric literals - ampersand-hash-num_literal-semicolon.

• Versions of the textlabel functions have been added to Core.Picture for escape-parsed text. It is useful for higher-level software to escape the text, do some calculations then render it - going back to un-escaped text for the rendering would be inefficient.

• The internal representation of paths has changed. They are now represented as start-point plus list of relative path segments rather than start-point plus list of absolute path segments. Using relative path segments makes it cheaper to move paths with translate, although calculating the bounding box and rendering to PostScript is more expensive. The rationale for the change is that to make complex pictures, paths are potentially moved many times but the other operations are only performed once.

• Internal change to Primitives and the PrimCTM - ellipses and labels no longer have a point (center or baseline left) as an element in the datatype, the point is now represented within the PrimCTM.

• Name change to Core.Picture API - the path construction function path has been renamed to primPath.

• Name change in Core.FontSize, the function textBoundsEnc has been renamed to textBoundsEsc. Wumpus-Core now calls strings that have been parsed for escape characters Escaped Text rather than Encoded Text.

• Fixed bug where ellipse rotation and scaling calculated the wrong bounding box.

• Fixed bug in illustrateControlPoints where the control points were drawn but the original primitive was lost.

• Added initial support for arbitrary SVG attributes (e.g. onmouseover handlers) via annotateGroup in Core.Picture. Arbitrary SVG "defs" can be written into the defs prologue by using writeSVG_defs instead of writeSVG. This functionality is mostly untested!

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• StephenTetley

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