OneCAD-Simulation/docs/control-protocol.md

Control protocol

fieldcraft --control PORT (or FIELDCRAFT_CONTROL_PORT=PORT) listens on 127.0.0.1:PORT for JSON lines. Each request is one line {"id": …, "method": "…", "params": {…}}; each reply is one line {"id": …, "ok": true, "result": …} or {"id": …, "ok": false, "error": "…"}. Requests are handled on the UI thread between frames; pointer and keyboard input is injected as real egui events, one pointer event per frame. The protocol has the same shape as SolidCraft's.

fieldcraft --sample --control 7070          # or --sample cantilever | impact
{"id":1,"method":"engine.execute","params":{"command":"model.info","params":{}}}
→ {"id":1,"ok":true,"result":{"elements":{"hex8":64,"tet4":162},"nodes":199}}
{"id":2,"method":"ui.render","params":{"path":"/tmp/model.png","width":900,"height":600}}

The channel is untrusted input. A request line may be at most 16 MiB; a longer one is answered with {"ok": false, "error": "request too large"} and the connection is closed, as are connections that send eight lines that are not JSON. At most 16 connections are served at once, at most 64 queued requests run per frame so a flood cannot starve drawing, and a request the UI thread has not answered within 60 seconds gets {"ok": false, "error": "timeout"} (a solve or a mesher is a job, answered when it ends however long it runs: see Jobs). Numbers are checked and clamped (drag steps, wheel lines, window size); ui.render refuses an image size out of range.

Engine

Method	Params	Result
engine.execute	command: command id, params: JSON object, wait? (default true)	the command's result; a solve or a mesher runs as a job
job.status	—	job: the running job (title, command, elapsed seconds, progress {step: {name, index, count}, stage, done, total}, fraction 0–1 when bounded, line as the window shows it), or null
job.wait	—	the running job's result when it ends (null job when none runs)
job.cancel	—	cancels the job (cancelled: what it was): its solver or mesher stops at its next increment, time step, supernode or refinement pass and what it made is dropped; the model stays as it was and every request waiting for it gets {"ok": false, "cancelled": true}
engine.script	commands: [{command, params}, …]	stops at the first error; journal: commands that changed the model so far
engine.commands	—	every command: id, label, params (the parameter documentation), schema (its parameters as JSON Schema) and requires (what the session must hold before it runs: design, geometry, nodes, mesh, analysable, material, step, result, …; engine.execute of a command missing one fails without doing anything, naming each missing piece and its toolbar entry)

Commands never open forms or file pickers when run this way. fieldcraft-cli commands prints the same registry. file.sample {name} opens a sample (parts, cantilever, impact) and solve.run {} solves every step; the Results workspace comes up when a result appears (a static step with its contours on the undeformed shape: results.deformed {} shows the deformed shape). The ribbon follows the commands run here, as it does for scripts, MCP, the command search and the browser: a command that changes the model or the results display brings the tab where its toolbar entry lives (Mesh for mesh.*, Properties, Steps, Loads & BCs… for model.*, Solve, Results), as a click there would. Queries (model.check, mesh.quality…) and the Tools tab's commands (files, undo, model.info) leave the ribbon where it is.

UI

Method	Params	Notes
ui.inspect	—	view settings (ui), camera, viewport rect (points), renderer (gpu/cpu) and adapter, open command form, status bar, node and element counts, the results display (results: what the results.* commands reply: view, stale, contour range, modes), the probed node (probe), solve (the title bar's Solve: enabled, and unavailable as ui.toolbar's entries give it, listing everything solve.run misses), busy (the background job: a file opening, a solve, a mesher run from its form by a click on OK), job (that job as job.status gives it), prompt ({"unsaved": path}, {"design": path} (a design of another part opened over a meshed or defined model), "recover", "samples"), recent (recent files), updates (docs/updates.md: automatic, checked_at, skip, available (a newer version the status bar offers), busy, staged, unsupported; null when the run does not check), selected (the browser's selected definition {kind, name}, or seed {kind: "seed", edge}), browser (each top-level browser node's setup state: [{node, state, tip, add}], state done, next, blocked (⚠: its command cannot run yet; tip says what it needs and where), todo, optional or null for nodes that are no setup stage, add its ghost rows {stage, label, command, status}; a ghost row's region is layout's browser/add/<stage>), nav (the left-drag mode), layout (each region of the window drawn last frame as [x, y, w, h] in points: app_bar, ribbon, workspace_switcher, document_tab, app_bar:<action>, browser, viewport, nav_bar, axis_view, selection_bar, legend (while results are shown), context, command_line, timeline, toolbar_dropdown, palette), version
ui.set	any view setting: style (shaded_edges, shaded, wireframe), show_nodes, show_geometry, show_mesh, show_loads (boundary condition and load symbols), show_interactions (reference points, couplings, contact and tie surfaces, rigid walls), symbol_size (the setup symbols' size on screen in points, 6–48, at any zoom), result_symbols (the shown step's setup symbols over a results plot; off by default), result_extremes (markers at a contour's largest and smallest value), perspective, dark, show_tree (the browser), show_timeline, nav_preset (the mouse navigation: fieldcraft, fusion, solidworks, inventor, alias, tinkercad, openscad; an unknown id acts as fieldcraft) and reverse_zoom (both remembered per user), workspace (prepare, model, analysis, results), tab (the toolbar tab: geometry, mesh, properties, assembly, steps, loads, interactions, solve, results, tools; a tab of another workspace brings that workspace), palette (the command search open), menu (the open menu: file, help, workspace, view, more, or a panel's drop-down as <tab>/<panel> such as mesh/Tet; null closes it)	an unknown setting or value is an error; returns the settings
ui.view	view: front, back, left, right, top, bottom, iso, home (iso and fit), fit	every view frames the model as drawn (the deformed shape included; the setup's symbols keep their size on screen and are not framed) in the part of the viewport the overlays (layout's legend, selection_bar, axis_view, nav_bar) leave free; fit keeps the direction of view. Opening another model, sample or design frames it in the home view (the same design opened again after an edit keeps the camera), and results that come up with part of the model out of sight are framed. Returns the camera
ui.camera	yaw, pitch (degrees), distance? (model units), target?, fit?, fov? (degrees)	turns the camera to any orientation about its target (with target, [x, y, z] or {"center_of": "mass" | "bbox", "bodies"?} as MCP screenshot's camera (docs/mcp.md), it moves to look at that target from distance, from the distance that fits the targeted bodies with fit, or from the one that keeps the whole model in view from every side; fov sets the perspective, 0 orthographic): yaw about Z (0 looks along +Y, the front view; −45 is the iso view's, −90 the right view's), pitch the elevation above the XY plane; distance moves the eye (the zoom of an orthographic view). Angles must be finite and the distance above 0: the yaw is wrapped, the pitch clamped to ±90 and the distance to 0.001–10⁹; anything else is an error. A sequence of calls orbits smoothly. Returns the camera (ui.inspect's, angles in radians)
ui.toolbar	—	the ribbon: workspace, workspaces, tab, tabs (the workspace's), menu (the open menu), panels (each panel label's menu key and rect), and every catalogue entry (docs/features.md) with id, label, tab, panel, command (null while coming soon), more (its related commands), coming_soon (the milestone, or null), enabled (false while coming soon or while its command misses what it needs), unavailable (null, or what its command misses: reason, the tooltip's lines such as "Needs a material — Properties › Material", and missing, each with requirement, what, provider (the command that provides it) and place (its toolbar entry)), fit — full (a button), collapsed (its panel is one button), more (its panel is in the » menu) or menu (in its panel's drop-down) — and rect (screen points, last frame, on the shown tab; for menu entries the row while the drop-down is open)
ui.start	command: a command or toolbar entry id	like a click on the toolbar, a drop-down row or a search result: a command without parameters runs, one with parameters opens its form in the context panel; an entry that is coming soon is an error naming its milestone. Never opens a native file picker: file entries (open, save as, write deck) open their command's form
ui.select	kind (set, material, section, step, boundary_condition, load, reference_point, coupling, contact, tie, fluid_domain), name; nothing to deselect	selects a definition as a browser click does; its properties (with Edit and Delete) show in the context panel
ui.select (viewport)	any of filter, box_mode, mode, clear, at, box, geometry, nodes, elements, faces (and no kind)	changes the viewport's selection (see Selection); returns ui.selection's reply
ui.selection	—	the viewport's selection: filter, box_mode (box selection on), count, capped, summary, items, params (the selection as a set's members), hover (what a click would pick under the pointer)
ui.prompt	answer: for unsaved save, discard or cancel; for design new (a new model with the design), keep (the design over the current model) or cancel; for replace_mesh replace (runs the form, replacing the mesh) or cancel (the form stays open); for delete (the item menu's Delete… or the Delete key: {delete: question, kind, name, users, allowed}) delete (with a datum's partitions when it has any; refused when allowed is false) or cancel; for recover recover (with id from file.recovery.list) or close; for samples open (with name) or close; for crashed (the start after a crash: {crashed: [reports]}) report (opens Report a Bug for the newest) or close; for crash_reports (Help › Crash Reports…, or ui.start diagnostics.crash_reports: {crash_reports: [reports]}) report (with id: opens Report a Bug for it), delete (with id), delete_all or close; for report_bug ({report_bug: draft}) set (any of title, observed, share_session, include_model; replies with the draft) or close — the browser opens only from a click (docs/crash-reports.md); for consent (the first run's question about anonymous usage) share or decline; for settings (Help › Settings…) set (any of usage_sharing, usage_automation; or update_check, update_skip (a version, "" for none)) or close (docs/privacy.md, docs/updates.md); for update (a downloaded and verified update: {update: state}) restart (saves or asks about unsaved changes first, then closes the window to install) or later (installs when the app quits)	answers the window's question (ui.inspect's prompt)
ui.settings	—	opens Help › Settings… (answered with ui.prompt); replies with the privacy state as ui.inspect's privacy gives it: available (this run may share usage), usage_sharing (null until asked), usage_automation, recording, queued
ui.item	kind (body, surface, or a definition kind as ui.select takes it, datum, partition), name, action: edit, rename, suppress/unsuppress (a datum or partition), hide, show, isolate, show_all, delete, or activate/deactivate with step	an item menu's entry, as a right click on the item and a click on the entry: runs the same command (rename opens the model.rename form filled in; delete opens the delete prompt, answered with ui.prompt)
ui.dialog	params? (JSON object, fills the form), use_selection?, run?, submit?, cancel?	drives the open command form, in that order; use_selection is the form's Target row (see Selection); run returns the command's result and closes the form on success; submit is the form's OK button: a mesher that would replace a body's mesh first asks (prompt replace_mesh, with the question and what else goes: sets listing the old labels, solved results), and meshers run in the background (busy); a form opened by another form's Create … button (a reference field with nothing to pick) goes back to that form on run (with the new item picked) or cancel
ui.click	x, y (screen points), button?: left/right/middle, shift?, ctrl?, alt?, double?	real pointer input; in the viewport a click selects what is under it (Shift adds, Ctrl/Cmd adds or removes, a click on nothing clears the selection), and a click on a results plot also probes the nearest node of the face under it (solve.probe; ui.inspect shows the values); with the Relax Nodes form open (mesh.node.relax) a click on the mesh places its sphere of influence instead (Alt + wheel sizes it)
ui.move	x, y
ui.drag	x0, y0, x1, y1, button?, shift?, ctrl?, steps? (1–200)	press, move, release: in the viewport the drag does what the navigation preset (ui.set {nav_preset}) binds; by default a left drag orbits about the model point under the press, or the centre of what is drawn from empty space (with box selection on, it selects the visible nodes, element faces or elements in the box; Ctrl + left from empty space still orbits), a right or middle drag (or Shift + left) pans
ui.scroll	x, y, delta? (wheel lines, −100–100; positive zooms in)	zooms toward the model point under x, y (the point at the target's depth over empty space), by the same factor per line in orthographic and perspective views; ui.set {reverse_zoom} turns it the other way
ui.key	key (egui key name, Enter, Escape…), cmd?, shift?	F over the viewport frames the model; Escape clears the selection (and then cancels an open form)
ui.text	text	typed text (into the focused field)
ui.drop	paths: 1–16 file paths	drops the files on the window: the next frame opens them as a drop from the file manager does, and as a file picked in the Open dialog does (a .fieldcraft model, a .solidcraft design, a .3mf tagged mesh; ui.inspect's busy while they open). The native picker cannot be driven over the channel; this is the same route
ui.worldToScreen	points: [[x, y, z]…] (at most 1000)	screen points in the viewport drawn last frame (null when not on screen)
ui.resize	width, height	window inner size in points
ui.fullscreen	on? (default true)	into or out of full screen; on macOS the title bar's left group moves into the traffic lights' room while there are none
ui.screenshot	path?	PNG of the window, taken a few frames later; waits for a presented frame; when none comes within 8 seconds (a hidden window, a locked screen) it answers with ui.capture's offscreen picture ("offscreen": true). Without path: fieldcraft-shot.png in the temporary folder
ui.capture	path?, width?, height? (points; default the window's), scale? (pixels per point, 0.5–4; default the window's)	PNG of the whole window (title bar, ribbon, open menus and search, panels, forms and the viewport) drawn offscreen, without fade-in animations: the UI pass runs in a separate egui context and is rasterised on the CPU, so it works with the window hidden, minimised or the screen locked. At most 8192 pixels a side and 16 megapixels. Without path: fieldcraft-shot.png in the temporary folder
ui.render	path, width? (default 1280), height? (default 800): whole pixels, each 1–8192 and at most 16 megapixels in all; scale? (pixels per point, 0.5–4, default the window's)	CPU render of the model with the current camera, view settings and selection highlight (no window or GPU needed). Symbols, lines and nodes are sized in points, so a render at the window's device resolution matches the window. A size out of range, or a scene over 20 million primitives, is an error
app.quit	—	closes the window

Selection

The viewport's selection belongs to the window, not the model: there is no engine command for it, and nothing about it is saved or journalled. What is selected is kept in the model's persistent terms, so it reads as a set definition: geometry by name ({"body", "face"}, or edge, vertex, or the body alone; a face picked on the mesh is named through the mesh's geometry tags, so it stays selected through a remesh) and the mesh by label (nodes, elements, element faces as {"element", "face"}). Labels the model no longer has drop out after an edit.

ui.select on the viewport takes, in this order:

• filter: what a pick selects: faces, edges, vertices, bodies (geometry), nodes, element_faces, elements (the mesh). The selection bar at the top of the viewport shows it.
• box_mode: true or false turns box selection on or off (a left drag draws the box).
• mode: how the items change the selection: replace (default), add, remove, toggle.
• clear: true: empty the selection first.
• geometry, nodes, elements, faces: items by name and label, as model.set.create takes them (at most 100 000 in each list; labels from 1).
• at: [x, y] in window points: pick there as a click does, with the filter (nothing under the point selects nothing; with replace it clears the selection).
• box: [x0, y0, x1, y1] in window points: the visible nodes, element faces or elements inside the box (other filters refuse a box). Faces in front hide what is behind them.

A selection holds at most 100 000 items; past that it is cut and capped is true. Picking runs on the CPU against the triangles the viewport draws (on the GPU too), with a watertight ray–triangle test: the nearest face wins, nodes, vertices and edges are the nearest on screen within a few pixels that are not hidden, and ties go to the lower index, so the same pick gives the same answer every time.

Command forms that apply to part of the model have a Target row with Use selection (ui.dialog {"use_selection": true}): model.set.create and model.set.edit take the selection as members; model.boundary_condition.*, model.load.*, model.section.* and model.coupling.* get a set made from it (model.set.create, named after the definition: Clamp-set, then Clamp-set-2…) in target: {"set"} or set. A right click in the viewport offers Create set from selection, which opens model.set.create's form filled in.

{"id":1,"method":"ui.view","params":{"view":"right"}}
{"id":2,"method":"ui.select","params":{"filter":"element_faces","box":[300,120,1100,700]}}
→ {"id":2,"ok":true,"result":{"count":8,"params":{"faces":[{"element":20,"face":4},…]},…}}
{"id":3,"method":"ui.start","params":{"command":"model.set.create"}}
{"id":4,"method":"ui.dialog","params":{"params":{"name":"end"},"use_selection":true,"run":true}}

Files

User clicks (title bar File menu, toolbar entries, Cmd/Ctrl+O, S, Shift+S), drops on the window and files named on the command line go through native file pickers and open in the background (ui.inspect's busy); commands sent here take their paths as parameters and run at once (file.open, file.save_as, geometry.open, geometry.import.mesh, deck.write).

Jobs

engine.execute of a solve (solve.run, solve.static, solve.nonlinear, solve.heat, solve.frequency, solve.buckle, solve.explicit, solve.fluid) or a mesher (mesh.tet.generate, mesh.hex.*, mesh.node.relax, mesh.plan.apply, mesh.cells) or a partition (geometry.partition) runs it off the window thread, as the Solve button and a mesher form's OK do: the window keeps drawing its progress (step, stage and count, elapsed time) with Cancel. The reply is the command's result when it ends, however long that takes; with "wait": false it is {"job": n} at once, and job.status, job.wait and job.cancel follow it. Cancel (the button or job.cancel) interrupts the running command: every solver and mesher checks for it at its natural points (increments and Newton iterations, time steps, fluid steps, Lanczos blocks, the factorization's supernodes, the tet mesher's refinement and improvement passes, the hex meshers' attempts) and stops with cancelled, leaving the model unchanged. One job runs at a time; another long command meanwhile is refused, naming the job. The MCP server's solve and mesh tools wait for the reply.

Heated flow results

A solved fluid step with temperature in every saved frame offers temperature in the Results field list and through results.contour, results.slice, results.surface and results.streamlines ({"field":"temperature"}). Slices and obstacle surfaces sample fluid-cell temperature; streamline colours sample temperature along the velocity traces. The legend and existing solve.probe use the model's temperature scale, without conversion. An isothermal step hides the field and rejects an explicit request with an explanation. The frame slider and results.frame select the field's time, including the initial frame.

results.surface {"field":"wall_heat_flux","frame":10} shows the signed heat received by each obstacle face divided by that face's complete tessellated geometric area. Positive values heat the wall; a hot wall heating the fluid is negative. This is a face average, not a resolved local distribution. The legend uses the model's consistent power/area unit: for mm–tonne–second it is mW/mm² (not W/mm²); other systems follow their own units.

Wall heat uses the recorded face-group histories, linearly interpolated at the shown frame only between recorded times. The initial frame precedes the history and remains uncoloured; no heat is invented or extrapolated. Recorded adiabatic faces are zero. Unrecorded/imported faces remain in their own colour. The command reply includes wall_heat.faces with body, face, area, power and flux (null when unavailable), plus the sign and sampling convention. This surface-only field suppresses the slice and leaves streamlines plain; selecting a cell field restores the saved slice settings. results.contour also selects the wall field and controls its bands/range. The desktop and headless picture use the same mapping and palette.