Curve-recovery additions: _as_entities for Node/StyledEntity/Rounded ClippedPolygon, silent-loss warning, sort-tolerant walks, opt-in partial recovery

CHANGELOG.md

@@ -4,6 +4,10 @@ The format of this changelog is based on
 [Keep a Changelog](https://keepachangelog.com/), and this project adheres to
 [Semantic Versioning](https://semver.org/).
 
+## Unreleased
+
+  - Added `recover_curves` and the curve-preserving Boolean variants `union2d_curved`, `difference2d_curved`, `intersect2d_curved`, and `xor2d_curved`, which recover original curves (arcs, splines) from a clipped result wherever their discretized footprint survived the operation intact, returning a `Vector{CurvilinearRegion}`
+
 ## 1.14.0 (2026-05-28)
 
   - Added `ParameterSet`, a nested dictionary wrapper with dot-access for reading and

docs/src/concepts/polygons.md

@@ -21,7 +21,7 @@ Geometric Boolean operations on polygons are called "clipping" operations. For 2
 
 !!! info
 
-    Boolean operations in 3D with `SolidModel` are handled by the Open CASCADE Technology kernel, which works directly with rich geometry types rendered from our native `CoordinateSystem`. If you need boolean operations involving curved geometry whose results can't be achieved by clipping-then-rounding, then your 2D geometry should defer the boolean operation until `SolidModel` postrendering so that the result will still be represented with curves.
+    Boolean operations in 3D with `SolidModel` are handled by the Open CASCADE Technology kernel, which works directly with rich geometry types rendered from our native `CoordinateSystem`. If you need boolean operations involving curved geometry whose results can't be achieved by clipping-then-rounding, you have two options: keep curves in 2D using the curve-preserving Boolean variants (see [Recovering curves through clipping](@ref) below), or defer the boolean operation until `SolidModel` postrendering so that the result will still be represented with curves.
 
 For many use cases, `union2d`, `difference2d`, `intersect2d`, and `xor2d` behave as expected and are easiest to use.
 More general operations may be accomplished using the `clip` function.
@@ -45,6 +45,34 @@ A [`CurvilinearRegion`](@ref) pairs a `CurvilinearPolygon` exterior with zero or
 
 See [API Reference: Curvilinear geometry](@ref api-curvilinear).
 
+### Recovering curves through clipping
+
+Boolean operations (`union2d`, `difference2d`, etc.) discretize curved geometry to polygons
+before passing them to the Clipper library. Normally, the original curves (arcs, splines)
+are lost in this process. The [`recover_curves`](@ref) function and its convenience
+wrappers (`difference2d_curved`, `union2d_curved`, `intersect2d_curved`, `xor2d_curved`)
+track each input curve's discretized integer-grid footprint and substitute the original
+curve back into the result wherever that footprint survived the boolean operation intact.
+
+The curve-preserving variants return a `Vector{CurvilinearRegion}` rather than a single
+`ClippedPolygon`. Each region in the vector corresponds to one outer contour in the clipped
+result (the disjoint pieces each become a separate region). For example:
+
+```julia
+# Standard clipping discretizes curves to polygons:
+result = difference2d(a, b)  # ClippedPolygon
+
+# Curve-preserving variant recovers arcs where possible:
+regions = difference2d_curved(a, b)  # Vector{CurvilinearRegion}, arcs preserved
+```
+
+**Current limitations:** A curve is recovered only if its entire discretized run survives
+the boolean operation with exact integer equality. If the operation cuts through a curve
+(e.g., a straight edge crossing an arc's interior), that curve falls back to a polyline.
+Additionally, curves can only be recovered on CurvilinearRegion/CurvilinearPolygon,
+Path nodes, and `Rounded`-styled `Polygon`/`Rectangle` entities. `Rounded` applied to
+other entities, styled Curvilinear entities, and nested styles do not yet support curve recovery.
+
 ## Styles
 
 In addition to other generic [entity styles](./geometry.md#Entity-Styles) like `NoRender`, `AbstractPolygon`s can be paired with the `Rounded` style. `ClippedPolygon`s support `StyleDict`, which allows for different styles to be applied to different contours in its tree.

docs/src/reference/api.md

@@ -194,6 +194,11 @@
     CurvilinearRegion
     Curvilinear.edge_type_at_vertex
     Curvilinear.line_arc_cornerindices
+    difference2d_curved
+    intersect2d_curved
+    recover_curves
+    union2d_curved
+    xor2d_curved
 ```
 
 ### [Shapes](@id api-shapes)

src/DeviceLayout.jl

@@ -563,7 +563,15 @@ include("render/render.jl")
 # After render.jl to ensure access to `to_polygons`
 include("curvilinear.jl")
 using .Curvilinear
-export Curvilinear, CurvilinearPolygon, CurvilinearRegion, pathtopolys
+export Curvilinear,
+    CurvilinearPolygon,
+    CurvilinearRegion,
+    pathtopolys,
+    recover_curves,
+    difference2d_curved,
+    union2d_curved,
+    intersect2d_curved,
+    xor2d_curved
 
 include("simple_shapes.jl")
 import .SimpleShapes: