aj
faa36d7539
Spec for adding NFP-based placement as a competing strategy in NestEngine.FindBestFill() for non-rectangular parts. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
91 lines
4.2 KiB
Markdown
91 lines
4.2 KiB
Markdown
# NFP Strategy in FindBestFill
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## Problem
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`NestEngine.FindBestFill()` currently runs three rectangle-based strategies (Linear, RectBestFit, Pairs) that treat parts as bounding boxes. For non-rectangular parts (L-shapes, circles, irregular profiles), this wastes significant plate area because the strategies can't interlock actual part geometry.
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The NFP infrastructure already exists (used by `AutoNest`) but is completely separate from the single-drawing fill path.
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## Solution
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Add `FillNfpBestFit` as a new competing strategy in `FindBestFill()`. It uses the existing NFP/BLF infrastructure to place many copies of a single drawing using actual part geometry instead of bounding boxes. It only runs when the part is non-rectangular (where it can actually improve on grid packing).
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## Design
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### New method: `FillNfpBestFit(NestItem item, Box workArea)`
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Located in `NestEngine.cs`, private method alongside `FillRectangleBestFit` and `FillWithPairs`.
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**Algorithm:**
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1. Compute `halfSpacing = Plate.PartSpacing / 2.0`
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2. Extract the offset perimeter polygon via `ExtractPerimeterPolygon(drawing, halfSpacing)` (already exists as a private static method in NestEngine)
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3. **Rectangularity gate:** compute `polygon.Area() / polygon.BoundingBox().Area()`. If ratio > 0.95, return empty list — grid strategies already handle rectangular parts optimally
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4. Compute candidate rotation angles:
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- Start with hull edge angles via `ComputeHullEdgeAngles(polygon)` (already exists in NestEngine)
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- Always include 0° and 90°
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- Filter by `NestItem.RotationStart` / `NestItem.RotationEnd` window (keep angles where `RotationStart <= angle <= RotationEnd`; if both are 0, treat as unconstrained 0–360°)
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5. Build an `NfpCache`:
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- For each candidate rotation, rotate the polygon and register it via `nfpCache.RegisterPolygon(drawing.Id, rotation, rotatedPolygon)`
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- Call `nfpCache.PreComputeAll()` — since all entries share the same drawing ID, this computes NFPs between all rotation pairs of the single part shape
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6. For each candidate rotation, run `BottomLeftFill.Fill()`:
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- Build a sequence of N copies of `(drawing.Id, rotation, drawing)` where N = `(int)(workArea.Area() / polygon.Area())` capped to a reasonable max
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- Place via BLF which uses IFP minus NFP unions to find valid positions
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7. Score each rotation's result via `FillScore.Compute(parts, workArea)`
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8. Return the parts list from the highest-scoring rotation, converted via `BottomLeftFill.ToNestParts()`
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### Integration into FindBestFill
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Insert after the Pairs phase, before remainder improvement, in both overloads of `FindBestFill`:
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```csharp
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// NFP phase (non-rectangular parts only)
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var nfpResult = FillNfpBestFit(item, workArea);
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Debug.WriteLine($"[FindBestFill] NFP: {nfpResult?.Count ?? 0} parts");
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if (IsBetterFill(nfpResult, best, workArea))
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{
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best = nfpResult;
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ReportProgress(progress, NestPhase.Nfp, PlateNumber, best, workArea);
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}
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```
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The progress-reporting overload also adds `token.ThrowIfCancellationRequested()` before the NFP phase.
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### NestPhase enum
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Add `Nfp` after `Pairs`:
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```csharp
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public enum NestPhase
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{
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Linear,
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RectBestFit,
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Pairs,
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Nfp,
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Remainder
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}
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```
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## Files Modified
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| File | Change |
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|------|--------|
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| `OpenNest.Engine/NestEngine.cs` | Add `FillNfpBestFit()` method; call from both `FindBestFill` overloads after Pairs phase |
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| `OpenNest.Engine/NestProgress.cs` | Add `Nfp` to `NestPhase` enum |
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## What Doesn't Change
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- `FillBestFit`, `FillLinear`, `FillWithPairs` — untouched
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- `AutoNest` — separate code path, untouched
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- `BottomLeftFill`, `NfpCache`, `NoFitPolygon`, `InnerFitPolygon` — reused as-is, no modifications
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- UI callers (`ActionFillArea`, `ActionClone`, `PlateView.FillWithProgress`) — no changes, they call `NestEngine.Fill()` which calls `FindBestFill()` internally
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- MCP tools (`NestingTools`) — no changes
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## Edge Cases
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- **Part with no valid perimeter polygon:** `ExtractPerimeterPolygon` returns null → return empty list
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- **All rotations filtered out by constraints:** no BLF runs → return empty list
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- **BLF places zero parts at a rotation:** skip that rotation, try others
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- **Very small work area where part doesn't fit:** IFP computation returns invalid polygon → BLF places nothing → return empty list
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