aj
fe2a293128
Clarify sort direction (ascending, keep nearest to origin), document parameter changes, MeasureDimension behavior, and behavioral trade-off. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
67 lines
3.6 KiB
Markdown
67 lines
3.6 KiB
Markdown
# Trim-to-Count: Replace ShrinkFiller Loop with Edge-Sorted Trim
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## Problem
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When a fill produces more parts than needed, `ShrinkFiller` iteratively shrinks the work area and re-fills from scratch until the count drops below target. Each iteration runs the full fill pipeline (pairs, bestfit, linear), making this expensive. Meanwhile, `DefaultNestEngine.Fill` trims excess parts with a blind `Take(N)` that ignores spatial position.
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## Solution
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Add `ShrinkFiller.TrimToCount` — a static method that sorts parts by their trailing edge and removes from the far end until the target count is reached. Replace the shrink loop and the blind `Take(N)` with calls to this method.
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## Design
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### New method: `ShrinkFiller.TrimToCount`
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```csharp
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internal static List<Part> TrimToCount(List<Part> parts, int targetCount, ShrinkAxis axis)
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```
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- Returns input unchanged if `parts.Count <= targetCount`
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- Sorts ascending by trailing edge, takes the first `targetCount` parts (keeps parts nearest to origin, discards farthest):
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- `ShrinkAxis.Width` → sort ascending by `BoundingBox.Right`
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- `ShrinkAxis.Height` → sort ascending by `BoundingBox.Top`
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- Returns a new list (does not mutate input)
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### Changes to `ShrinkFiller.Shrink`
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Replace the iterative shrink loop:
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1. Fill once using existing `EstimateStartBox` + fallback logic (unchanged)
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2. If count exceeds `shrinkTarget`, call `TrimToCount(parts, shrinkTarget, axis)`
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3. Measure dimension from trimmed result via existing `MeasureDimension`
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4. Report progress once after trim
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5. Return `ShrinkResult`
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Parameters removed from `Shrink`: `maxIterations` (no loop). The `spacing` parameter is kept (used by `EstimateStartBox`). `CancellationToken` is kept in the signature for API consistency even though the loop no longer uses it.
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### Changes to `DefaultNestEngine.Fill`
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Replace line 55-56:
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```csharp
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// Before:
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if (item.Quantity > 0 && best.Count > item.Quantity)
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best = best.Take(item.Quantity).ToList();
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// After:
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if (item.Quantity > 0 && best.Count > item.Quantity)
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best = ShrinkFiller.TrimToCount(best, item.Quantity, ShrinkAxis.Width);
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```
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Defaults to `ShrinkAxis.Width` (trim by right edge) since this is the natural "end of nest" direction outside of a shrink context.
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## Design Decisions
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- **Axis-aware trimming**: Height shrink trims by top edge, width shrink trims by right edge. This respects the strip direction.
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- **No pair integrity**: Trimming may split interlocking pairs. This is acceptable because if the layout is suboptimal, a better candidate will replace it during evaluation.
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- **No edge spacing concerns**: The new dimension is simply the max edge of remaining parts. No snapping to spacing increments.
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- **`MeasureDimension` unchanged**: It measures the occupied extent of remaining parts relative to `box.X`/`box.Y` (the work area origin). This works correctly after trimming.
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- **`EstimateStartBox` preserved**: It was designed to accelerate the iterative loop, which is now gone. It still helps by producing a smaller starting fill, but could be simplified in a future pass.
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- **Behavioral trade-off**: The shrink loop found the smallest box fitting N parts; trim-to-count reports the actual extent of the N nearest parts, which may be slightly less tight if there are gaps. In practice this is negligible since fill algorithms pack densely.
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## Files Changed
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- `OpenNest.Engine/Fill/ShrinkFiller.cs` — add `TrimToCount`, replace shrink loop, remove `maxIterations`
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- `OpenNest.Engine/DefaultNestEngine.cs` — replace `Take(N)` with `TrimToCount`
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- `OpenNest.Tests/ShrinkFillerTests.cs` — delete `Shrink_RespectsMaxIterations` test (concept no longer exists), update remaining tests, add `TrimToCount` tests
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