Regions & compartments

A region is an area cut into one slab: a chamber, a reservoir, a well, a mixing cavity. Unlike a channel it has no route and no ends. It is a shape in the plan, and channels reach it by landing on its wall.

Compartments

A region is divided into compartments, and the compartment is what you select, name and edit. A newly drawn region holds exactly one, which the app presents as the region itself — no compartment row, no extra tier to navigate. Divide it and each piece gets a row of its own.

Every compartment has one of two fills, and the two words for them run through the whole app.

Void is carved: the fluid is there. A void compartment is a pocket, and it carries its own depth, wall profile and corner radii — which is what makes a shallow antechamber beside a deep well, or a step in a chamber’s floor.

Material is untouched slab: the fluid is not there. A material compartment is a hole, and it is how you author a post standing in a chamber, an island, or a wall between two halves of one shape.

Switching a compartment’s fill is the whole grammar. A pocket switched to material becomes a hole and the slab closes over it; a hole switched back becomes a pocket and is carved out. The direction that would leave material inside material is disabled, and the tooltip says which case applies.

Nested shapes

Drawing inside a compartment produces its opposite. Inside a chamber you draw a hole — an island of slab standing in the void. Inside that hole you draw a pocket — a void carved into the island. The alternation repeats as deep as you need it.

A pocket set inside a pocket is never isolated from it: the two meet along the boundary and are one continuous void differing only in depth. Separating a void from the void around it takes a hole between them, which is the physically honest answer rather than a rule the app checks for.

A region needs at least three vertices in every ring, so deleting a vertex is refused at three.

The weld

Two shapes drawn independently never share a boundary exactly — their vertices land a hair apart, and a hair of material between two chambers is a wall you did not ask for. Welding is how a shared boundary is made exact: place a vertex on an existing wall and the shape you are drawing is joined to what you clicked, with no partition between them.

Four rules follow, and they are worth knowing before you meet them.

• Click a wall twice and the run of wall between the two clicks comes along. A corridor off a chamber is four clicks, two of them on the wall.
• A shape whose last wall click can reach the first one along the wall closes itself — there is nothing left to click.
• Starting off the wall switches the self-closing off, which is what you want for a shape that meets one wall in two separate places.
• When you do not want the wall between two clicks, put a vertex off the wall between them. The chip says place a vertex off the wall when it cannot route an edge any other way.

The chip at the cursor names what the release will make throughout — weld to, carve, split into, or the reason it is refused — so a refusal is never a surprise. The preview outlines the assembled ring, drawing borrowed vertices more faintly than the ones you placed, so what the tool brought along is visibly not yours.

Seams and movement

Welded compartments share their run of boundary exactly, and such a run is a seam rather than a wall. The app draws it as a hairline to say so: it is the one stretch of a compartment’s outline that fluid crosses.

Welding also merges the shapes into one movable unit. Drag a welded compartment and its neighbours come with it — there is no piece left behind. A shape set inside another, a hole in a chamber or a pocket in a hole, is not welded to it and moves on its own.

Welding onto a region that is a separate child absorbs it: its shape joins the one you drew and it stops being a child of its own. That is refused where it would destroy something you wrote — a position bound to an expression, or a label a pin sources — and the chip says which.

Compartment removal

Deleting a compartment removes that piece where the region is divided, and the whole shape where it is not. It is refused while a channel lands on that compartment’s wall, since the alternative is silently moving a landing onto a wall you never chose.

Removing a piece is also how a wall is authored at the top level of a region, where a hole cannot go: carve a chamber into three and every piece is a pocket, so deleting the middle one lets the slab close over it and leaves the two ends separated. One tier down — inside a pocket — the wall can instead be a hole with a row of its own.

Compartment names

A compartment with no name of its own reads a derived one: region for the compartment that is the region, and hole 1, pocket 2, hole 3 numbered among its siblings. Those numbers are positional, so removing a sibling renumbers the rest. Name a compartment where you need the label to stay put.

Placement

The outermost compartment carries the region’s own pos, rot and layer, so moving the region moves everything inside it. A nested compartment carries dx, dy and rot instead, which move it within the shape that contains it. There is no layer row on a nested compartment: everything in one region is cut into one slab.

Regions in the network

A region is not a connection. Channels reach it only through wall-bound points, and a region with no wall-bound points on it is a passive cavity — a shape in the slab that nothing flows into.

See also

• Channels & points — wall-bound points and how a channel breaks into a wall.
• Inspector — the fill control, the compartment detail and the Body tree.
• Layers, stacks & processes — the slab a region is cut into.
• Fabrication overrides — the depth, walls and corner radii a pocket carries.
• Keyboard & mouse reference — the Draw region tool’s keys.