📖 Glossary#

One-line definitions for the terms that appear across the rest of the documentation, grouped by subject and alphabetized within each group.

Scene and Constraints#

Center mode: How the pivot for a Spin or Scale operation is resolved. One of Centroid (vertex centroid at runtime), Fixed (a user-entered coordinate), Max Towards (centroid of vertices furthest along a direction), or Vertex (a single vertex picked in Edit Mode).
Contact gap: Separation distance the solver enforces between surfaces, specified per group or per collider as an absolute Blender-unit value or as a ratio of the group’s bounding-box diagonal. See Material Parameters.
Cross-stitch anchor: Per-vertex barycentric data recorded during a Snap, tying each source-object vertex to a target triangle so the stitch survives small mesh edits.
Embedded Move: A marker the add-on puts on a pin by itself when Make Keyframe writes per-vertex keyframes on it; it is not offered in the pin’s Add dropdown. It tells the encoder where to splice the per-vertex track in, so the pinned vertices follow the hand-animated or scripted pose sequence during the solve. Deleting the keyframes removes it again.
Intersection allowance: An opt-in that accepts already-overlapping geometry instead of refusing to simulate it. Two are set on a group and apply to every object assigned to it (Allow Self-Intersections, Allow Inter-Object Intersections), and one is set on a pin (Allow Intersections Here). “Self” means one object’s overlap with itself, so two objects in one group make an inter-object pair. Each suppresses the report only; contact still acts on the overlap. See Allow Intersections.
Invisible collider: A parametric wall or sphere that acts as a collision boundary for the simulation without being rendered in Blender. Walls are infinite planes; spheres support invert (inside-surface collision) and hemisphere (bowl shape) flags. See Invisible Colliders.
Merge pair: Two snapped objects registered as a solver stitch constraint, optionally with explicit stitch anchors. Created by the snap operator and stored on the scene. See Snap and Merge.
Object group: One of up to 32 slots on a scene that holds a type (Solid / Shell / Rod / PDRD / Sand / Static), material parameters, assigned meshes, and pins. See Object Groups; Static groups are covered separately in Static Objects.
Operation: A keyframed action stacked on a pin: Move By, Spin, Scale, or Torque. Torque is exclusive with the other three, and a pin that carries keyframed per-vertex animation (its Embedded Move marker) accepts none of the four at all. See Pins and Operations.
Overlay color: Per-group viewport tint that shows which objects belong to which group. Defaults by group type and can be overridden per group.
PDRD: Group type for exactly-rigid bodies. The surface mesh moves as a single best-fit rigid transform, so no tetrahedralization is needed. Short for Painless Differentiable Rotation Dynamics.
Pin: A named set of vertices on an object, registered as a simulation constraint target. On meshes this is a regular Blender vertex group; on curve objects (which have no vertex groups) the add-on stores the control-point indices in an internal _pin_<name> custom property on the curve. Stacks operations on top, optionally with pull strength or a pin duration.
Pin duration: A frame limit that releases a pin at a specified frame, handing the affected vertices back to free dynamics mid-simulation.
Pull strength: Soft-force magnitude that replaces a hard pin constraint, pulling vertices toward their target positions rather than holding them rigidly.
Rod: Group type for 1D structures (ropes, wires, threads). Accepts mesh and curve objects.
Sand: Group type for granular bodies, simulated as a particle cloud rather than a connected mesh.
Shell: Group type for thin deformable surfaces (cloth, fabric). Accepts mesh objects.
Snap: One-shot alignment that translates object A so its closest vertex lands on the nearest point of object B’s surface – the nearest triangle for a mesh or solid target, the nearest segment for a rod. Typically followed by a merge pair registration.
Solid: Group type for volumetric deformable bodies.
Static: Group type for non-deforming collision objects (ground planes, props, mannequins). Exposes friction and contact settings; motion is driven by Blender transform keyframes rather than by the solver.
Stitch stiffness: Strength of the soft force that holds a stitch together, set per-merge-pair (or per-group for loose edges), default 1.0. The stitch is always a soft force, never an exact weld, and is exposed for every supported pair: Shell-Shell, Shell-Solid, Rod-Shell, Rod-Solid, Rod-Rod, Solid-Solid, and any dynamic group stitched to a Static collider.
Torque: A pin Operation that applies rotational force around an axis derived from the pinned vertices. Exclusive with Move By, Spin, and Scale, and refused outright on a pin that carries keyframed per-vertex animation (Embedded Move).
UUID registry: Per-object UUID assignment maintained by the add-on. Keeps group references stable across rename operations so merge pairs, assigned objects, and pin vertex groups survive object renames.

Parameters and Simulation#

Bake: Converts the live PC2-plus-modifier preview into standard Blender animation: shape keys and fcurves on meshes, or per-control-point keyframes on curves. The baked result renders without the add-on installed. See Baking Animation.
Bend stiffness: Per-group resistance to bending, carried by Shell and Rod groups as a single bend value that each type scales on its own terms. On a rod it is measured against a one-centimeter reference segment, so a strand bends the same way however many segments it is drawn with. See Bend Stiffness on a Rod.
Checkpoint: A saved, resumable solver state captured at a chosen frame. Add frames to the Save Checkpoints list to have the solver write a checkpoint at each, or let Auto Save record them at a fixed interval. Saved checkpoints are what the Resume picker lists, so the simulation can be continued from any of them later.
Constitutive model: The mathematical model that governs how a group deforms (for example Baraff-Witkin, Stable NeoHookean, or ARAP). Available choices depend on group type: Shell offers Baraff-Witkin and ARAP, Solid offers Stable NeoHookean and ARAP, Rod is locked to ARAP.
Dynamic parameter: A scene-level parameter whose value is keyframed over time. Seven can be: gravity, wind, air density, air friction, vertex air damp, step size, and inactive momentum frames. They are keyframed on their own Scene Configuration sliders as ordinary Blender F-curves — there is no dynamic-parameter sub-panel — then sampled per frame, uploaded with the rest of the parameters at transfer time, and replayed by the solver during the run. See Dynamic Parameters.
Fetch: Downloads per-frame vertex data from the solver and wires it up to each simulated object so the timeline plays back the result.
JupyterLab integration: A first-class path for driving the solver from a notebook on the solver host, including headless runs and parameter sweeps without Blender open. See JupyterLab.
Material parameter: A per-group property that controls deformation, density, stiffness, friction, and contact. The applicable fields depend on the group’s type. See Material Parameters.
Mesh hash: A topology fingerprint (vertex, polygon, edge, and object counts, the vertex count of every pin group, and a digest of each captured Static deformation; no UV data enters it) recorded at transfer time and compared again before Run, Resume, and Fetch. A mismatch means the Blender mesh no longer matches what the solver has.
PC2: Point Cache 2. The per-object vertex cache the add-on writes locally on Fetch (data/<blend name>/<object uuid>.pc2, built from the solver’s own vert_N.bin frames on the remote), replayed as the timeline plays — through a MESH_CACHE modifier on meshes, and through a frame handler on curve rods, which carry no such modifier. Blender frames 1..N map to remote frames 0..N-1.
Profile: A named preset saved to a TOML file: either a scene profile (scene parameters, dynamic parameters, and invisible colliders) or a material profile (one group’s material parameters). Loaded and saved from the profile dropdown next to the relevant panel.
Rayleigh damping: Velocity-dependent energy loss proportional to a group’s material stiffness, set per group by Deformation Damping and Bending Damping (both default 0.0, which disables it). It calms high-frequency jitter without slowing down the bulk motion of the body. Deformation Damping applies to Solid, Shell, and Rod groups; Bending Damping applies to Shell and Rod groups only. This is distinct from air damping, which acts on the whole scene.
Resume: Continues a paused or partially completed simulation from a saved state, preserving earlier results. The panel’s single Resume button opens a picker listing every saved checkpoint, so you choose which one to continue from; frames before it are kept and the rest are overwritten. It stays available after a failed run as long as the solver still holds at least one saved checkpoint.
Run: Starts the simulation on the remote solver. Warns on a stale mesh hash and clears prior simulation output before beginning.
Scene parameter: A whole-scene setting (frame range, step size, gravity, wind, air properties, solver tolerances) applied globally rather than per group. See Scene Parameters.
Shrink: Rest-shape scale carried in a group’s material parameters: anisotropic Shrink X / Shrink Y on Shell, a single uniform Shrink on Solid, and a per-segment rest-length scale on Rod. Below 1.0 the rest shape is smaller than the drawn geometry, so the body pulls itself taut; above 1.0 it is larger, so the body slackens. See Material Parameters.
Solver state: The status the Backend Communicator panel shows on its “Status: …” line, one of twenty-three values: Disconnected, Waiting for Server Start…, Ready to Run, Simulation Running…, Resumable, Fetching Animation…, Simulation Failed, Protocol Version Mismatch, and the transient ones in between.
Transfer: Uploads geometry, pins, colliders, and every parameter to the solver and rebuilds its scene. Required whenever topology or group membership changes.
Update Params on Remote: Re-encodes and uploads parameters without resending geometry, for fast iteration on dynamics and materials.

Connections and Integrations#

Communicator: The add-on’s single connection manager. It owns all remote operations from a background thread so the UI never blocks on the network.
Connection profile: A saved TOML entry capturing every connection field of the Backend Communicator panel for one host, used to switch between hosts and share presets across a team. See Connection Profiles.
Docker connection: A connection type where the solver runs inside a Docker container on a local Docker daemon. See Docker (Local).
Docker over SSH: A connection type where the solver runs in a container on a Docker daemon reached through SSH, for environments where the administrator hands you a container rather than shell access. See Docker over SSH.
execute_shell_command: MCP tool that runs arbitrary shell commands on the connected solver host, through the active connection backend - a different machine entirely for the SSH-based types, and inside the container for the Docker ones - and only while a connection is live. Paired with run_python_script, which runs inside Blender, as an escape hatch for provisioning and maintenance tasks not yet covered by dedicated tools.
Local connection: A connection type where the solver runs on the same host as Blender, reached over a loopback socket. See Local.
MCP resource: A read-only asset exposed by the MCP server via resources/read, covering live scene snapshots (blender://scene/current) and the bundled llm://<topic> markdown docs.
MCP server: The bundled Model Context Protocol server on localhost:9633 that exposes add-on operations as JSON-RPC tools for external agents. See MCP Server.
MCP tool: A JSON-RPC method exposed by the MCP server and dispatched with tools/call. Goes through the same validation layer as the sidebar buttons.
Protocol version: The wire protocol version between the add-on and the ppf-cts-server binary. Both halves take it from the same shipped file, so the pair that ships together always agrees and there is no number for you to set. TCMD requests carry a 4-byte big-endian length prefix between the b"TCMD" header and the payload, and the server supports heartbeat recovery on long-running operations. CBOR envelope payloads on this connection use the schema from the ppf-cts-formats crate. The server advertises its version on connect; a mismatch means one of the two binaries is stale, surfaces as a protocol-version-mismatch status, and refuses to proceed. See Protocol version mismatch.
Python API (add-on): The add-on’s Python API, exposed under bl_ext.user_default.ppf_contact_solver.ops.api and imported from Blender’s text editor or a notebook. Covers the same validation layer as the sidebar and the MCP server. See Blender Python API.
run_python_script: MCP tool that evaluates arbitrary Python inside Blender. Exists for operations the add-on does not yet expose as first-class tools; see the security note in MCP Server.
ppf-cts-server: The Rust solver binary (ppf-cts-server on Linux, ppf-cts-server.exe on Windows) launched on the remote side (or as a local subprocess for Windows Native) that listens for work over TCP on the configured port (default 9090). Built from the ppf-cts-server crate, which wraps the algorithmic core in ppf-cts-core.
Session ID: Per-connection identifier the add-on mints at connect (12 hex characters) and stamps on the artifacts that run produces. Persisted with the .blend on save so a reopened file can detect whether the remote has been reset since the file was saved.
SSH Command mode: A connection backend that parses host, port, username, and key path out of a plain ssh … string. Convenient when the command is pasted from a deployment script but brittle if your real config depends on ~/.ssh/config wildcards.
SSH connection: A connection type where the solver runs on a remote Linux host reached by SSH, with credentials entered as explicit fields. See SSH.
Streamable HTTP: The MCP transport profile (protocol version 2025-06-18) used by the bundled MCP server. All traffic goes through a single /mcp endpoint with a server-assigned Mcp-Session-Id.
Windows Native connection: A connection type where the solver runs directly as a Windows subprocess, using a bundled Python interpreter and no SSH or Docker. See Windows Native.