Rhino 8

In Rhino, the pipeline is a sequence of commands, numbered in workflow order. Each reads and writes named layers under TopologyProblem::, and the session state is kept with the document, so it survives between commands and a save and reopen.

The commands are the scripts in rhino_plugin/commands/. They run on Rhino 8's CPython 3.9; see Installation to install the package there.

Commands

Command	Step	What it does
CMD00_start	1	Reset the project: empty the TopologyProblem layers and recreate them. The settings stay.
CMD99_settings	1	Show and edit the settings of this document.
CMD01_boundary_selection	2	Pick the outer boundary, holes, point features and guides.
CMD02_coarse_mesh	3	Choose the frame-field or the skeleton route, and build the coarse layout.
CMD02_read_coarse_mesh	3	Read a coarse layout drawn by hand over the domain boundaries, instead of generating one.
CMD03_edit_coarse_mesh	4	Edit the coarse layout by hand: move a corner or a pole, cut a new line along a drawn polyline or arc, unzip a run of corners into a strip, remove a strip, undo. Nothing is written until you commit.
CMD04_densities	5	Pick a strip and set its density, or set a target length for every strip.
CMD05_dense_pattern	5	Set the pattern of each coarse patch: ortho, diagonal or fan.
CMD06_quad_mesh	6	Densify the coarse layout into the quad mesh.
CMD07_smooth	7	Smooth the whole mesh or a region, optionally with guide curves, from one option line.
CMD08_dual	8	Take the dual of a picked quad mesh.
CMD09_edit_quad_mesh		Edit the final mesh by hand: move or remove vertices, edges and faces, draw new edges, add or remove a line of quads. The result no longer has to be all quads. Densifying the layout again discards the edit.
CMD99_session_save / CMD99_session_open		Save the whole project to one JSON file, or open one into this document.
CMD99_mesh_export		Export one picked mesh to a JSON file a script can load again.
CMD99_clear		Clear chosen layers to start over.

Densities are matched to strips by geometry, never by strip number, because a layout read back from Rhino can come back with its strips renumbered.

Using the commands

Reading a drawn layout (CMD02_read_coarse_mesh)

Draw the outer boundary on Outer, holes on Inner and the coarse division lines on Skeleton::EdgeCurves. All three layers are read as edges of one network; the layer only says which edges are walls, and so which closed region is a hole.

• A polyline is split at its own corners; a smooth curve (arc, circle, interpolated curve) is one edge.
• Every curve is split where another curve meets it. Snap ends onto the curve they land on (End, Near, Int): an end that stops short is refused as dangling.
• A piece of EdgeCurves lying along a wall only marks corners on that wall. A disc as one patch is its circle on Outer and four arcs of it on EdgeCurves.
• A dangling curve, a division outside the domain or inside a hole, a piece touching nothing else, a patch that is not a quad or a triangle, or two curves between the same corners stop the command with the curve selected. Nothing is repaired; a triangle is kept as a pseudo-quad.
• With no Outer curve, the divisions carry the outer boundary themselves.

Editing the coarse layout (CMD03_edit_coarse_mesh)

• move_vertices: drag a corner. A corner on the layout boundary stays on the domain wall.
• move_pole: pick a highlighted pole, then one of the highlighted corners it may move to. Only a corner all its patches share is allowed.
• add_polyedge: draw a polyline or an arc from one layout edge to another. Every edge crossed is split and every patch passed through is split in two; the drawn shape is kept. A run that stops inside is carried on along its strip to the wall.
• add_strip: pick a run of existing corners, Enter to add; each corner is unzipped into two and a new strip opens between them. Esc cancels the run.
• divide_strip: pick a strip and split it down the middle.
• remove_strip: pick a strip; it is deleted at once and the two sides weld together.
• undo goes back one edit, reset back to the start of the command, commit writes the layout back to the session.

Nothing is written until commit. A move keeps the strip densities and patterns; a topology change drops them. A layout that will not densify is refused at commit. Every operation keeps the layout all-quad, so a line always runs the full width of the layout: from boundary to boundary, or closed on itself.

Densities and patterns (CMD04_densities, CMD05_dense_pattern)

CMD04_densities: Pick a strip and type its number of elements, or set Target_length or Target_density for every strip at once. Strips are drawn as ribbons shaded by density; Clear drops the picks and returns every strip to the target. The densities are stored on the layout and are lost when the layout is rebuilt; they are then re-set from the target.

CMD05_dense_pattern: choose a pattern, then pick patches one at a time (Pick), several at once (Pick_multiple) or all (All). Finish keeps them for CMD06_quad_mesh.

Densifying (CMD06_quad_mesh)

Each coarse edge is densified along its real shape: walls from the curves on InputBoundaries, interior edges from the layout's own polylines. Read the printed coarse edges tally: chord counts edges densified as straight lines, and on a curved domain it should be interior edges only. A field solved for a different outline or different solver settings is ignored, with a message to rerun step 3. Rerunning this step discards any edit made in CMD09_edit_quad_mesh.

Smoothing (CMD07_smooth)

Pick the mesh, answer Whole or Region, set the options and press Enter:

• Algorithm: Area, Centroid, CenterOfMass or ForceDensity. A region is always smoothed by area.
• Boundary: Sliding keeps every boundary vertex on its outline with the corners pinned; Fixed pins the boundary; Free holds nothing, so only fixed vertices and guides anchor the mesh.
• FixedVertices: vertices that do not move, picked or taken from the points on PointFeatures.
• Guides: pick a guide curve, or AllGuides for every curve on Guides, and a chain of mesh vertices along it is proposed. Edit it with Add, Remove and Clear and set its Hold (Fixed or Sliding).

ForceDensity cannot hold a vertex on a curve: a sliding boundary keeps only its corners, and a guide vertex is pinned where it lands. The result is baked to QuadMesh::Smoothed::<algorithm>, or ::Relaxed for a region.

Editing the final mesh (CMD09_edit_quad_mesh)

The mesh no longer has to be all quads here.

• move_vertex: drag a vertex; one on the boundary stays on the wall.
• remove_vertex, remove_edge, remove_face: remove the element (a removed edge merges its two faces).
• draw_edges: draw a polyline across the mesh; every edge crossed and face passed through is split. Loose ends inside a face are trimmed.
• add_line / remove_line: add a strip beside the line through a picked edge, or remove the strip through it. Only where the mesh is still quads.
• relax smooths the interior with every boundary held; undo and reset go back.

Every edit happens at once, and undo is where a wrong pick goes. A successful save bakes to QuadMesh::Edited and ends the command; this session's starting mesh is kept on QuadMesh::Unedited.

Projects and exports (CMD99_session_save, CMD99_session_open, CMD99_mesh_export)

CMD99_session_save writes the settings, domain, layout, field and dense mesh to one JSON file, which a plain Python script opens with SingularSession.load(path). CMD99_session_open reads it back; the domain is drawn only into empty input layers. One Ctrl+Z undoes the whole open. CMD99_mesh_export writes one picked mesh to JSON; read it back with Mesh.load_from_json(path). A mesh the session drew keeps its attributes (strips, densities, edge curves).

Settings (CMD99_settings)

The settings are stored in the .3dm. CMD01_boundary_selection, CMD04_densities and CMD06_quad_mesh also change single settings through the same store.