slop-cad

Appearance

The document model ​

This is the page to read first, because body here does not mean what it means in other CAD tools.

What a document is ​

A document is an ordered list of sketches. Each sketch may have one extrude. A sketch together with its extrude is a feature.

A sketch sits on one of two things. Either the world plane, making it a base sketch, or a face of an earlier feature's solid, making it a face sketch.

The timeline labels base sketches Sketch, Body 2, Body 3. It labels face sketches by which face they are on: Sketch on top face, Sketch on face #4.

Blends hang off the document rather than off any sketch, because an edge belongs to the finished shape rather than to any one feature.

There is one solid ​

Every feature is folded, in order, into a single solid.

Pressing New body appends another base sketch on the world plane, and what it extrudes is a solid of its own. Sketches drawn on a face belong to whichever solid they are standing on, so a feature never has to be told which body it builds.

The Bodies panel lists every solid the document builds:

  • Each row has an eye. Hiding a body takes it out of the view, out of face picking and out of an export, so an export matches the view it was taken from.
  • Click the name to rename it. The name is used everywhere the body is referred to, including the combine picker. Empty it to go back to the number.
  • The swatch paints the whole body. The colour is written onto its parts, so the timeline swatch still recolours one feature on its own afterwards.
  • The × deletes the body: its sketches, its features and its blends go with it, along with any combine or joint that named it. The last body is refused, because a document is always at least one sketch; Clear is what starts over.
  • The picker below joins two bodies, cuts one with another, or keeps only the part they share. The body you combine with is consumed, so the two rows become one.
  • Keeping shared is the operation that has no equivalent on a single feature: it needs two whole solids to compare.

Every combine you ask for is listed underneath in the order it is applied, phrased as what it did rather than as what you picked. Removing a row undoes that one combine and puts the body it consumed back, whether or not it was the last one asked for.

A combine parts the two solids' touching faces by a few microns before it runs, because faces that lie exactly on each other are what the kernel cannot resolve. On a part of ordinary size that is a millimetre or so of volume, and never a change you can see.

Bodies keep their numbers. Combining two of them does not renumber the rest, so Body 3 is still Body 3 after Body 2 is consumed.

A joint is the other thing two bodies can do to each other, and it is the opposite of a combine: nothing is consumed and nothing is fused. One body is held against the other, so moving the holder carries what it holds, and the two stay two.

What a part is ​

Each feature also produces its own shape on its own, called a part. That is what the per-feature colours in the model view are showing, and it is what the swatch in the timeline recolours.

Parts are not separate solids either. They exist so the tool can work out reference frames, re-derive a sketch plane after an edit, resolve a face pick back to the feature that owns it, and give you a visual sense of which feature contributed which material.

What you see, measure, and export is the folded solid. If a boolean step fails, you may briefly see the parts instead, and the timeline says so in amber.

Order ​

Features build in timeline order, which is creation order. There is no reordering. The rollback marker sets how many of them are built, so an early feature can be edited with the later ones out of the way. A feature made while the marker is back lands at the end of the list, and the marker returns there.

Blends are the exception. They always apply after every extrude, wherever their row sits, because an edge does not exist until both faces meeting at it do.

Why it is built this way ​

One solid is a simplification, and it buys something specific: every feature can be expressed as a union or a difference against a single accumulating shape, so the rebuild is one linear pass. That keeps rebuilds fast enough to run on every keystroke in a dimension field, which is why the parametric behaviour feels immediate.

The cost is paid wherever a part would be easier to describe as several independent solids at once, and it stays paid until bodies become a grouping of their own.

See also ​