SVG (.svg)

Scalable Vector Graphics output for 2D meshes — a write-only visualization format that draws the mesh edges.

Format name	svg
Extensions	.svg
Read / Write	— / ✓
Extra dependencies	—

Reading & writing

There is no reader — register_format is called with read=None. Full write signature:

import meshioplusplus

meshioplusplus.svg.write(
    "out.svg", mesh,
    float_fmt=".3f",
    stroke_width=None,
    image_width=100,
    fill="#c8c5bd",
    stroke="#000080",
)

• float_fmt — coordinate number format.
• stroke_width — edge stroke width; if None (default), auto-computed as 1% of the mesh's on-canvas width.
• image_width — output SVG width in user units, default 100 (not None) — deliberately non-trivial because some SVG viewers (e.g. eog) mis-render images whose natural width is close to 1 unit.
• fill / stroke — cell fill and edge colours, defaulted to match ParaView's default rendering colours (per an inline source comment).

File structure

A single <svg> root containing one <path> element per drawable cell (not <polygon>) — chosen deliberately: the comment in the source notes that svgo (a common SVG optimizer) converts <polygon>s to <path>s but drops style information when it does so, so meshio++ emits paths directly to sidestep that.

Path d templates (space-separated coordinate pairs, float_fmt-formatted):

cell type	path template
line	M x0 y0L x1 y1 (open, no closing Z)
triangle	M x0 y0L x1 y1L x2 y2Z
quad	M x0 y0L x1 y1L x2 y2L x3 y3Z

Points must be flat 2D: if points.shape[1] == 3, every z coordinate must be ~0 (atol=1e-14), else WriteError. The y-coordinate is flipped (max_y + min_y - y) to convert from the mesh/math convention (y-up) to SVG's screen convention (y-down).

Cell types

line, triangle, quad only. Any other cell block present in the mesh is silently dropped — no warning at all (unlike most other meshio++ writers' warn-and-skip convention for unsupported cell types).

Data mapping

None consumed — point_data/cell_data/field_data are ignored entirely; only geometry and cell connectivity affect the output.

Quirks & limitations

• No diagonal/winding correction on quad cells — a "crossed" (non-convex, bowtie) node ordering renders incorrectly with no error raised.
• Non-line/triangle/quad cells vanish from the output silently.
• Write-only; there is no way to read an SVG back into a Mesh.

Notes

• Backed by the C++ core (write_svg) with a pure-Python fallback: meshioplusplus.svg.write uses the C++ writer for real file paths and falls back to Python for file-object/buffer targets or on any error. Registered in the shared dispatch registry, so it is also reachable from the WASM, C API, and Fortran flat bindings (write-only, fixed default styling — per-call style options are exposed only through the Python write).
• tests/test_svg.py writes each mesh, checks the output parses as SVG with one <path> per drawable cell, and cross-checks that the C++ and Python writers agree on the path count. cpp/tests/test_svg_tikz.cpp covers the C++ writer directly (path count, closed vs open paths, colour/scaling options, unsupported-cell skipping, the non-flat WriteError).