Concepts and Data Flow

Outlines and strokes are different

The paths in an outline font describe the outer contours and holes of characters. They indicate where to fill, not in what order to move a pen.

This library therefore distinguishes two types of data:

FontOutlineGlyph, FontFilledGlyph, and FontCenterlineGlyph: data obtained by geometric processing of outline fonts.
FontStrokeGlyph: stroke data that preserves stroke order and pen-down/pen-up units.

The centerline-extraction route prioritizes applicability to arbitrary fonts, whereas the KanjiVG route prioritizes natural stroke segmentation and stroke order for kanji.

Intermediate representations

FontOutlineGlyph

A collection of outline paths for one character or a string. Points are scaled to the specified character height. For multiple characters, the paths are placed along the X axis using the font’s advance width and the specified spacing.

FontFilledGlyph

A binary mask obtained by projecting outlines onto a grid at a fixed spacing. Multiple outlines are combined using XOR, allowing outer contours and inner holes to be distinguished.

FontCenterlineGlyph

A collection of centerline paths obtained by skeletonizing the binary mask and tracing it as an 8-connected graph. Paths are split at branch points and endpoints.

FontStrokeGlyph

A collection of ordered stroke paths. The path order is the writing order, and each FontStrokePath represents one continuous pen-down stroke.

Separation of responsibilities

Stage	Class	Main responsibility
Outline extraction	`FontOutlineExtractor`	Convert font instructions into point sequences and scale to the specified height
Filling	`FontGlyphFiller`	Convert outlines into a binary grid
Centerline extraction	`FontCenterlineExtractor`	Skeletonization and path tracing
Centerline cleanup	`FontCenterlineCleaner`	Remove short paths and duplicate points; resample paths
Kanji strokes	`FontKanjiVGStrokeLoader`	Preserve KanjiVG stroke order when producing point sequences
Alphabet strokes	`FontAlphabetStrokeBuilder`	Generate point sequences from built-in single-line characters
Visualization	`FontViewer`	Visually inspect intermediate representations
Physical writing	`FontBcapCobottaWriter`	Convert to absolute P coordinates and operate COBOTTA

Principles of robotic writing

COBOTTA distinguishes motion within a stroke from motion between strokes:

Move to the start of a stroke with the pen raised.
Lower the pen to the writing surface at the start point.
Submit consecutive points within the stroke at the same Z coordinate.
Raise the pen at the end of the stroke.
Move to the start of the next stroke.

Robot targets are absolute P coordinates referenced to the initial writing pose, not relative movements. The orientation components remain those of the initial pose; only XYZ is transformed from character coordinates.