OpenNest/docs/nesting-engines.md

Nesting engines

Whole-job engines implement INestingEngine.Solve(NestJob) and are selected by name through NestingEngineRegistry. Every automatic nesting front end validates engine output the same way; see automatic nesting and validation.

Built-in engines

Engines are named for the jobs they suit, not for how or by whom they were built. Engine code lives in OpenNest.Engine/NestingEngines/<Name>/, its tests in OpenNest.Engine.Tests/NestingEngines/.

Engine	Best for	Method
Rectangles	Plain and near-rectangular plates	Each part packed as the box of its material at its minimum-area rotation, using a maximal-rectangles free list; stock chosen sheet by sheet by salvage-credited look-ahead cost
Irregular	Irregular profiles	No-fit-polygon frontier packing with gap filling and best-fit pairs, six whole-job strategy variants and a tail re-plan
StockLadder	Caller-supplied stock ladders	Constrained-first fill with equivalent-demand area repacking
Default, Strip, Vertical Remnant, Horizontal Remnant	Single-strategy fills	The fixed placement strategies behind interactive fill

Rectangles places irregular parts validly, but only as their bounding boxes; it never nests into a notch or hole. Box sides account for how the layout check flattens arcs, so round-edged parts stay valid at box contact.

Interactive/full-area box packing uses the same 90% work-area slack allowance as Rectangles. A free box may absorb a slightly oversized side only at its right/top edge when that edge coincides with the plate work-area boundary. Internal leftover edges keep the strict packing tolerance, and actual part dimensions still determine spacing away from the plate boundary.

Irregular fills gaps and open notches using outer profiles; it does not yet place parts inside enclosed cutouts. For a part with two or more copies it also offers its best-fit pairs (two copies interlocked, as the Best Fit viewer shows them) alongside the single copies, and places a pair where both members' free regions allow it. Each pair's internal spacing is re-checked with the layout check before it is offered, and only rotations the part's policy allows are used. A pair may introduce legal rotations beyond the sampled single poses; these remain eligible even when none of the sampled singles fits the stock. Both members block space separately, leaving their notches and intervening gaps available for later parts. Concave no-fit polygons are prepared with a single boundary/containment union. Any remaining numerical hole is filled only when its entire ring is certified to lie in forbidden space, preserving genuine enclosed placement pockets without changing spacing tolerances.

When remaining demand exceeds two, Irregular also offers Default Fill patterns as optional multi-member candidates, not as solid bounding boxes or a whole-job Default fallback. It searches the empty work area and physical leftover space for up to two high-area rectangles. Occupied outlines are expanded by part spacing before rectangle search. Each sheet prepares blocks initially and after its first placement, for up to four high-demand-area types; each type has at most eight new Fill preparations per spacing per solve. Repeated rectangles reuse private drawing/candidate caches. Quantity-one and quantity-two requests never run block Fill.

Block members are trimmed to remaining demand, mapped back to source-frame rotations, and checked for legal rotations and internal material clearance before competing with singles and pairs. Group-only rotations do not expand the single-part rotation choices. Placement intersects all member free regions and subtracts each placed member separately, preserving usable gaps. A failed or invalid Fill proposal leaves singles and pairs available. Large enclosed-pocket blocks remain pending the hole-geometry integration; containment cutting order and shop-use safety acceptance remain separate sequencer/verification work.

Renamed engines

Earlier releases shipped these as plug-ins under other names. The registry maps the old names so saved desktop selections, scripts and API requests keep working:

Old name	Now
Opus55NestingEngine	Irregular
RectanglesNestingEngine	Rectangles

Gpt6Astra and Qwen38FlashNext are no longer shipped and have no alias. A saved selection of either falls back to Default with the usual status-bar warning.

Changing an engine

• A change lands only when it beats the engine's current result on OpenNest.Benchmark for the jobs that engine targets, with every layout valid. Report cost, validity, unplaced parts and time.
• Placement must be deterministic: no clocks, unseeded randomness or environment variables. Budget work by counting it; wall time may stop work only through the cancellation token.
• Keep each engine's tests passing, including EngineContractTests<TEngine> (quadrants, overflow, priority, cancellation, stock and plate limits, determinism). Every layout in those tests is checked with NestLayoutCheck, the benchmark's validator.
• Engines may share code. Move a helper into shared Engine code when a second engine needs it, rather than copying it.

Plug-ins

External engines still load from an Engines/ folder beside the desktop, console, MCP or benchmark executable. A plug-in implements INestingEngine with a public parameterless constructor and registers under its CLR type name. A plug-in whose name matches a built-in engine, or a renamed engine's old name, is skipped: a leftover OpenNest.Engine.Opus55.dll cannot shadow Irregular. Leftover Gpt6Astra or Qwen38FlashNext DLLs still load as ordinary plug-ins until deleted.