build123d-drafting-helpers 0.1.1

Third-party drawing-annotation helpers for build123d — dim_linear, leader, view_axes, lint_drawing

build123d-drafting-helpers

Third-party drawing-annotation helpers for build123d — pure Python, no MCP dependency. Not affiliated with the upstream build123d project.

from build123d_drafting import dim_linear, leader, view_axes, lint_drawing

The install name is build123d-drafting-helpers; the import name is build123d_drafting.

Not to be confused with baverman/build123d_draft — that project is modelling shortcuts (slot helpers, rotation aliases, build_line wrappers), not drafting/annotation. Different scope despite the similar name.

Installation

pip install build123d-drafting-helpers

Or with uv:

uv add build123d-drafting-helpers

Requires build123d >= 0.7.0 and Python ≥ 3.10.

Helpers

dim_linear(p1, p2, side, distance, draft, label=None, tolerance=None)

ExtensionLine wrapper with named placement side instead of raw signed offset.

draft = Draft(font_size=2.5, decimal_precision=1)
dim = dim_linear((-20, -10, 0), (20, -10, 0), "below", 8, draft, label="40")

side accepts "above" / "below" / "left" / "right" or an explicit world-direction vector. The correct offset sign is computed from the path direction's right-hand normal — no guessing.

Returns a DimResult(shape, label_str, measured_length).

---

safe_dim_line(path, label, draft, fallback_label=None)

DimensionLine wrapper that won't raise ValueError when the label is wider than the dim path. Truncates gracefully and retries.

---

leader(tip, elbow, label, draft)

Leader annotation built from scratch. The line stops cleanly before the label text.

res = leader((5, 5, 0), (20, 12, 0), "⌀7.93 H7", draft)
exporter.add_shape(res.lines, layer="dims")   # arrowhead + shelf — fill_color layer
exporter.add_shape(res.text,  layer="text")   # glyphs — fill_color layer

Returns LeaderResult(lines, text, label_str, tip, elbow). Route lines and text to separate SVG layers, both with fill_color set.

---

view_axes(viewport_origin, viewport_up=(0,1,0), look_at=(0,0,0))

Returns the world→page axis mapping for a project_to_viewport call, computed analytically.

axes = view_axes((0, 0, -100), (0, 1, 0), (0, 0, 0))
# {"world_X": ("page_X", -1.0), "world_Y": ("page_Y", 1.0), "world_Z": ("depth", 0.0)}
# ↑ bottom view flips world-X on the page

---

lint_drawing(items, part_bbox=None)

Structural checks on a list of DimResult / LeaderResult objects:

• Label numeric value differs from measured path length by >0.5% (likely axis swap)
• Dim bbox overlaps part outline by >10% (dim placed inside the view)
• Leader elbow point inside label bbox (line strikes through text)

issues = lint_drawing([dim1, dim2, lea1])
for issue in issues:
    print(issue.severity, issue.message)

---

iso_title_block(...) and surface_finish_mark(...)

iso_title_block is a standalone title box (170 × 16 mm by default), positioned by the caller. It is not a substitute for build123d.TechnicalDrawing, which is a whole-page chrome — page-sized border + grid ticks + embedded title box, returned as a single Sketch. Use TechnicalDrawing when you want the full drawing-sheet frame; reach for iso_title_block when you want just the title box, positionable anywhere, with separate lines/text Compounds for SVG layer routing, and with material / general_tolerance fields that TechnicalDrawing does not carry.

surface_finish_mark produces an ISO 1302 Ra-value check-mark symbol — build123d does not ship one.

Status against upstream

• lint_drawing is a prototype of rule-based drawing checks that build123d's roadmap mentions as future work. If upstream ships its own linter later, this one can be deprecated.
• dim_linear is a thin convenience wrapper over ExtensionLine — it does not replace the underlying class, it just lets you write side="above" instead of computing the right-hand-normal signed offset by hand. If upstream adds a named-side parameter, this helper becomes redundant.

Development

git clone https://github.com/pzfreo/build123d-drafting-helpers.git
cd build123d-drafting-helpers
uv run pytest tests/

Status

Alpha. API may change. Developed alongside build123d-mcp, which integrates these helpers into its LLM-facing drawing workflow.

Documentation

• Drafting conventions and gotchas — offset sign table, crash modes, recommended feedback loop, and when to reach for which helper.