Non-destructive, partial surface extrudes/revolves/sweeps etc

[adamchalmers]

This proposes a new way to surface extrude/revolve/sweep for sketch 2. Part of KittyCAD/modeling-app#10386

Background

Currently, the engine extrude/revolve/sweep/etc endpoints take an entire sketch as their target. That worked fine for sketch 1 solid extrudes (where the sketch is a closed profile) and for surface extrudes (where the sketch could be closed or open, either way, it extrudes each segment separately).

Problem

In sketch 2, the user might want to surface extrude only some segments in the sketch. Like in the below example, only k of the n segments are selected for extrusion.

Right now the API doesn't allow for this. Clients send the ID of the overall sketch, and the server extrudes the whole thing. There's no way to only surface extrude k of the n segments.

Solution

Instead of extruding an entire sketch (solid2D) at once, we instead take a list of segments and extrude each of those separately.

Here's a motivating example:

In this example, after extruding:

• C becomes a single-surface body
• D and E become a polysurface (D is extruded into one surface, E into another)
• A and B become a single-body surface by default (because they're collinear) unless the user opts out by setting a keepSeams flag in KCL.

We want to:

• Keep the old path segments A-E existing, unchanged (same IDs).
• Create new bodies (Solid3Ds) from them.
  • Frontend cannot predict the number of bodies in advance (because frontend doesn't know which segments intersect, or are collinear).
  • So engine will need to tell the frontend how many bodies were created, and what their IDs are.
• Get a mapping between segments and surfaces, so that tags can transfer.
  • e.g. frontend must know that:
  • segment A and B were absorbed into body 1 face 0
  • segment C became body 2 face 0
  • segment D became body 0 face 0
  • segment E became body 0 face 1

Ideally we would not need any follow-up calls to query these bodies. Let's just send back all relevant information in the Extrude response.

Here's my proposed return for Extrude. I'm using YAML because it's more concise, but we'd actually be sending JSON. See the attachment for syntax highlighting, or copypastable here:

bodies:
  - id: body0
    surfaces:
      - faceIndex: 0
        faceId: <uuid>
        fromSegments: [d0000000-0000-0000-0000-000000000000]
      - faceIndex: 1
        faceId: <uuid>
        fromSegments: [e0000000-0000-0000-0000-000000000000]
  - id: body1
    surfaces:
      - faceIndex: 0
        faceId: <uuid>
        fromSegments: [a0000000-0000-0000-0000-000000000000, b0000000-0000-0000-0000-000000000000]
  - id: body2
    surfaces:
      - faceIndex: 0
        faceId: <uuid>
        fromSegments: [c0000000-0000-0000-0000-000000000000]

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[davreev]

Sounds good to me. If two consecutive segments are selected, would we still get two separate bodies or would they be merged into a single one?

[adamchalmers]

Sounds good to me. If two consecutive segments are selected, would we still get two separate bodies or would they be merged into a single one?

Good question. I'll ask @max-mrgrsk and @nicboone8. Perhaps it should be configurable.

[nicboone8]

I would expect them merged by default, but making it configurable is a good idea

[graphite-app]

Documentation inconsistency: Revolve.target still says "Must be a closed 2D solid" but should be updated to "Must be a 2D sketch" to match the Extrude operation and reflect support for partial surface revolves via the new segments field.

Suggested change

	/// Which sketch to sweep.
	/// Must be a closed 2D solid.
	pub target: ModelingCmdId,
	/// If given, extrude each of these segments into a separate body with the given ID.
	#[serde(default, skip_serializing_if = "Option::is_none")]
	pub segments: Option<Vec<IdPair>>,
	/// When two collinear segments are extruded, what should happen?
	/// If true, creates a body with two surfaces.
	/// If false, creates a body with one surface, spanning both collinear segments.
	#[serde(default)]
	#[builder(default)]
	pub keep_seams: bool,
	/// Path along which to sweep.
	pub trajectory: ModelingCmdId,
	/// If true, the sweep will be broken up into sub-sweeps (extrusions, revolves, sweeps) based on the trajectory path components.
	/// Which sketch to revolve.
	/// Must be a 2D sketch.
	pub target: ModelingCmdId,

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