SVG#

.svg write only

Summary of the specification#

Scalable Vector Graphics is the W3C’s XML picture format: a <svg> root whose viewBox names the drawing’s coordinate extent and whose width and height, when present, say how large to render it. Shapes are children of the root; a <path> is spelled by its d attribute as a sequence of commands - M moves, L draws a line, Z closes the outline - and a <g> groups shapes under shared presentation attributes such as stroke and fill. The y axis runs downward. Coordinates are unitless user space, scaled to the rendered size through the viewBox.

An SVG is a picture, not a mesh. It carries no third coordinate, no element type and no attribute, so the mesh cannot be recovered from it: polyxios writes the format and refuses to read it.

Specification at a glance#

structure	XML: `<svg viewBox="…">` holding one `<g>` of `<path>` elements
element record	`<path class="<type>" d="M x y L x y … Z">`, one per element type
coordinates	the mesh’s own units, y mirrored, the top-left corner at the origin
style	`fill="none" stroke="black" stroke-width="…"` on the group
size	`viewBox` always; `width` / `height` on request

SVG 1.1 (W3C) ↗

Reading#

Not supported. polyxios.read() raises UnsupportedFormatError naming the file, so a pipeline that tries to round-trip through .svg fails at once rather than at the next step.

Writing#

import polyxios as px

px.write(mesh, "out.svg")
px.write(mesh, "out.svg", plane="xz", width=800, stroke_width=0.02)
px.write(mesh, "out.svg", float_fmt=".3f")

plane picks the projection: "xy" (the default), "xz" or "yz", the first axis running rightward and the second upward. width sets the rendered width in CSS pixels, the height following from the mesh’s aspect ratio; without it the picture fills whatever displays it. stroke_width is the line weight in the mesh’s own units and defaults to a hundredth of the picture’s shorter side. float_fmt is the format specifier for every number written, .6g by default; one whose fill character is an XML delimiter (", <, >, &) is refused, since every number lands in an attribute. Any other option is warned about and ignored.

Quirks worth knowing#

Coordinates go out in the mesh’s own units, shifted so the picture’s top-left corner is the origin and the upward axis mirrored, since SVG’s y grows downward; the viewBox is the mesh’s extent padded by half a stroke so an outline on the boundary is not clipped. Passing width scales the picture without touching the coordinates.
Lines and faces are drawn: a line, polyline, triangle, quadrilateral, pixel, polygon or triangle strip, and the higher-order kinds of each through their corner nodes, a triangle strip as one ring per triangle. Every other element type - a vertex, a solid cell - is skipped with a warning, one per type, so a volume mesh writes as an empty picture with a warning per cell type; extract its surface first. An element of a free-size type with too few nodes to outline is skipped the same way. A vertex coordinate that is not finite is refused outright: it would leave the viewBox undefined and the whole picture with it.
Each drawn type is one <path> carrying the type’s name as its class, its elements as subpaths in mesh order, so a stylesheet can colour triangles apart from quadrilaterals. vertex_attrs, element_attrs, the tags and global_attrs have no spelling in a picture and are not written.
The coordinate the projection drops is expected to be constant across the mesh. When it is not, the picture is still written and a warning says which axis varies and that the drawing is a projection. A flat mesh off the origin’s plane - every vertex at z=7 - is flat and warns about nothing.
A picture with no extent in one direction - a single horizontal line - takes its stroke from the other; one with no extent at all takes a stroke of one unit. Both still get a viewBox with area, from the padding.
.svg.gz is written compressed like every other format. .svgz, the conventional name for a gzipped SVG, is not registered.