111 lines
4.9 KiB
Markdown
111 lines
4.9 KiB
Markdown
# Iterative Shrink-Fill Design
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## Problem
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`StripNestEngine` currently picks a single "strip" drawing (the highest-area item), shrink-fills it into the tightest sub-region, then fills remnants with remaining drawings. This wastes potential density — every drawing benefits from shrink-filling into its tightest sub-region, not just the first one.
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Additionally, `AngleCandidateBuilder` does not include the rotating calipers minimum bounding rectangle angle, despite it being the mathematically optimal tight-fit rotation for rectangular work areas.
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## Design
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### 1. IterativeShrinkFiller
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New static class in `OpenNest.Engine/Fill/IterativeShrinkFiller.cs`.
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**Responsibility:** Given an ordered list of multi-quantity `NestItem` and a work area, iteratively shrink-fill each item into the tightest sub-region using `RemnantFiller` + `ShrinkFiller`, returning placed parts and leftovers.
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**Algorithm:**
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1. Create a `RemnantFiller` with the work area and spacing.
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2. For each multi-quantity item (sorted by priority ascending, then area descending), provide a fill function to `RemnantFiller` that internally:
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- Calls `ShrinkFiller.Shrink` with `ShrinkAxis.Height` (bottom strip direction).
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- Calls `ShrinkFiller.Shrink` with `ShrinkAxis.Width` (left strip direction).
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- Returns the parts from whichever direction produces a better `FillScore`.
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3. Collect any unfilled quantities into a leftovers list.
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4. Return placed parts, leftovers, and the `RemnantFinder` state for a subsequent pack pass.
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**Interface:**
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```csharp
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public class IterativeShrinkResult
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{
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public List<Part> Parts { get; set; }
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public List<NestItem> Leftovers { get; set; }
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}
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public static class IterativeShrinkFiller
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{
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public static IterativeShrinkResult Fill(
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List<NestItem> items,
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Box workArea,
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Func<NestItem, Box, List<Part>> fillFunc,
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double spacing,
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CancellationToken token);
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}
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```
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The class composes `RemnantFiller` and `ShrinkFiller` — it does not duplicate their logic.
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### 2. Rotating Calipers Angle in AngleCandidateBuilder
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Add the rotating calipers minimum bounding rectangle angle to the base angles in `AngleCandidateBuilder.Build`.
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**Current:** `baseAngles = [bestRotation, bestRotation + 90°]`
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**Proposed:** `baseAngles = [bestRotation, bestRotation + 90°, caliperAngle, caliperAngle + 90°]` (deduplicated)
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The caliper angle is pre-computed and cached on `NestItem.CaliperAngle` to avoid recomputing the pipeline (`Program.ToGeometry()` → `ShapeProfile` → `ToPolygonWithTolerance` → `RotatingCalipers.MinimumBoundingRectangle`) on every fill call.
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This feeds into every downstream path (pruned known-good list, sweep, ML prediction) since they all start from `baseAngles`.
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### 3. CaliperAngle on NestItem
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Add a `double? CaliperAngle` property to `NestItem`. Pre-computed by the caller before passing items to the engine. When null, `AngleCandidateBuilder` skips the caliper angles (backward compatible).
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Computation pipeline:
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```csharp
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var geometry = item.Drawing.Program.ToGeometry();
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var shapeProfile = new ShapeProfile(geometry);
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var polygon = shapeProfile.Perimeter.ToPolygonWithTolerance(0.001, circumscribe: true);
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var result = RotatingCalipers.MinimumBoundingRectangle(polygon);
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item.CaliperAngle = result.Angle;
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```
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### 4. Revised StripNestEngine.Nest
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The `Nest` override becomes a thin orchestrator:
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1. Separate items into multi-quantity (qty != 1) and singles (qty == 1).
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2. Pre-compute and cache `CaliperAngle` on each item's `NestItem`.
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3. Sort multi-quantity items by `Priority` ascending, then `Drawing.Area` descending.
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4. Call `IterativeShrinkFiller.Fill` with the sorted multi-quantity items.
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5. Collect leftovers: unfilled multi-quantity remainders + all singles.
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6. If leftovers exist and free space remains, run `PackArea` into the remaining area.
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7. Deduct placed quantities from the original items. Return all parts.
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**Deleted code:**
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- `SelectStripItemIndex` method
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- `EstimateStripDimension` method
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- `TryOrientation` method
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- `ShrinkFill` method
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**Deleted files:**
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- `StripNestResult.cs`
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- `StripDirection.cs`
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## Files Changed
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| File | Change |
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|------|--------|
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| `OpenNest.Engine/Fill/IterativeShrinkFiller.cs` | New — orchestrates RemnantFiller + ShrinkFiller with dual-direction selection |
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| `OpenNest.Engine/Fill/AngleCandidateBuilder.cs` | Add caliper angle + 90° to base angles from NestItem.CaliperAngle |
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| `OpenNest.Engine/NestItem.cs` | Add `double? CaliperAngle` property |
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| `OpenNest.Engine/StripNestEngine.cs` | Rewrite Nest to use IterativeShrinkFiller + pack leftovers |
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| `OpenNest.Engine/StripNestResult.cs` | Delete |
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| `OpenNest.Engine/StripDirection.cs` | Delete |
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## Not In Scope
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- Trying multiple item orderings and picking the best overall `FillScore` — future follow-up once we confirm the iterative approach is fast enough.
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- Changes to `NestEngineBase`, `DefaultNestEngine`, `RemnantFiller`, `ShrinkFiller`, `RemnantFinder`, or UI code.
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