Resize a constrained CAD plate

Lesson 6 · Level: intermediate · Workspace: CAD Editor #/model · Units: mm

A rectangle can be drawn from four independent corner coordinates, or produced from a constrained sketch whose points must satisfy horizontal, vertical and fixed-point relationships. This lesson uses the second approach. You will drive the plate with width and height while the accepted model maintains the supported geometric constraints.

This is a bounded source-backed learning exercise, not an interactive general-purpose sketch constraint solver. The published website, device/browser/GPU workflow, and physical file dialog are separate verification stages.

1. Load the actual constrained profile

In a workspace with Node 22+ and dependencies installed:

pnpm --filter @barocss/cad-editor build:library
pnpm --filter @barocss/cad-editor-app dev

Open http://127.0.0.1:52010/#/model (or the Vite port followed by #/model). In Model a part:

1. Open Modeling examples → Choose an example and select Resize a constrained plate.
2. If another accepted model exists, save it if needed and check Replace accepted model and discard its history and pending dimensions.
3. Select Load example; wait for Accepted model.
4. Select the named part under Visible output body if applicable.

The preset has one authored output (part), not separate stock/cutter outputs. Merely changing the example picker selection does not replace the current part.

2. Understand the visible numeric drivers

The inspector exposes two friendly controls for this exact preset:

Inspector label	Named parameter	Initial value	Changes
Profile X width	width	32 mm	Horizontal X extent of the solved profile
Profile Y height	height	24 mm	Vertical Y extent of the solved profile

The plate's extrusion thickness is fixed at 8 mm along +Z in this example. Profile Y height is not thickness. The authored example contains an additional lockY:0 value for a precise fixed-corner consistency condition, but it is intentionally not exposed as an editable UI control. Do not look for a free "lock Y" slider or ask this lesson to modify a different saved model's arbitrary constraint graph.

This is one exact constrained-polygon recipe. The authoring callback creates four points and ordered fixed, horizontal, vertical and another fixed constraint. The initial fourth-point X value of 1 mm is a solver seed, not a claim that the accepted outline has a sloping left side; the qualified solution resolves that X to 0. The solver's recorded baseline reports rank 8, zero degrees of freedom, with one consistent redundant corner constraint. Those statements describe this fixture, not all CAD sketches.

3. Resize, accept, undo

Start with the accepted 32 × 24 × 8 mm plate.

1. Change Profile X width to 40. The status Dimension changes pending means you have only entered a draft; native geometry has not yet been accepted.
2. Choose Apply dimensions. After Accepted model, inspect the part output and its exact native volume.
3. Use Undo to return to the 32 mm-width plate. Redo returns to the accepted 40 mm width. A pending draft must first be applied or cleared with Discard draft.
4. From the original accepted 32 mm-width state (not the wider state), set Profile Y height to 16 and Apply dimensions. Observe a shorter in-plane Y profile without changing the fixed Z thickness.

These values come from the separately adopted native provider's executed fixture—not newly observed browser screenshots:

Accepted native state	Width × Y height × Z thickness	Qualified part volume
Baseline	32 × 24 × 8 mm	6144 mm³
Width edit from baseline	40 × 24 × 8 mm	7680 mm³
Y-height edit from original baseline	32 × 16 × 8 mm	4096 mm³

The baseline provider separately recorded six native faces, eight topology vertices and twelve native edges. Its genuine preview uses 24 face-local vertices and 12 triangles. Native topology and display vertices must not be conflated.

4. Know what can refuse

The provider fixture deliberately exercises a conflicting internal lockY:1 edit and receives a native CONFLICT refusal. You cannot reproduce that exact control in this preset's UI because lockY is deliberately hidden. It proves that inconsistent fixed-point constraints should be rejected, not that the current editor has a general constraint authoring/dragging panel.

An unsupported dimension or failed profile/native/display qualification must preserve the previous accepted model, history and saved authored data. Keep the actual error, correct the draft, or choose Discard draft. Do not present a mocked editor response as a fresh native failure or tell users to bypass consistency by silently moving fixed points.

Even though the solution looks rectangular, it was authored as a constrained polygon, not as the engine's direct rectangle sketch. It therefore does not inherit rectangle-only hole, union, difference or Boolean shortcuts. This separate workflow cannot be repurposed as an unrestricted constraint-driven CAD feature graph.

5. Save, open and make another edit

Open Save or open a model and choose Download model. Verify the browser really saved part.cad.json. Use Choose model file to stage its UTF-8 text in Saved model data. File selection alone does not perform the native Open.

Check Replace accepted model and discard its history and pending dimensions, then select Open saved model. Once accepted, change Profile X width or Profile Y height again. The authored file retains points, constraints, named dimensions and the extrusion—not a cached solver preview or screenshots. The exact preset labels appear only for an authored graph matching its expected nodes/parameters, so a different imported graph may show generic numeric fields.

The file staging reader rejects empty input, malformed UTF-8 and data larger than 262,144 bytes; explicit Open separately validates the authoring contract. A refusal should preserve the last accepted state.

What the evidence actually supports

The native constrained-profile API and reference cite adopted provider #1835 and the real modeling-constrained-profile.ts public sample. The retained genuine baseline transfer is 292,980 bytes and includes the actual six-face convex part and 24-vertex/12-triangle baseline preview.

The editor's receiving/controller tests reuse that baseline under a mocked Worker; edited-state meshes and responses are mocks, not fresh captures. These checks establish bounded software behavior and refusal retention, not real browser pixels, GPU compatibility or physical file persistence.

External visual gate still open: constrained plate editor #1865 separately tracks physical/device acceptance. No synthetic screenshot, general sketch editor, global constraint solver, commercial CAD certification or mass/tolerance guarantee is implied by this lesson. Live browser/GPU/file tests are UNRUN in this documentation change.

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