Add Environment.Operation

Sources/SwiftSCAD/Environment/EnvironmentReader.swift

@@ -25,13 +25,17 @@ public func EnvironmentReader(@UnionBuilder3D body: @escaping (Environment) -> a
 }
 
 public extension Geometry2D {
-    func readingEnvironment(@UnionBuilder2D _ body: @escaping (Environment) -> any Geometry2D) -> any Geometry2D {
-        EnvironmentReader2D(body: body)
+    func readingEnvironment(@UnionBuilder2D _ body: @escaping (any Geometry2D, Environment) -> any Geometry2D) -> any Geometry2D {
+        EnvironmentReader2D { environment in
+            body(self, environment)
+        }
     }
 }
 
 public extension Geometry3D {
-    func readingEnvironment(@UnionBuilder3D _ body: @escaping (Environment) -> any Geometry3D) -> any Geometry3D {
-        EnvironmentReader3D(body: body)
+    func readingEnvironment(@UnionBuilder3D _ body: @escaping (any Geometry3D, Environment) -> any Geometry3D) -> any Geometry3D {
+        EnvironmentReader3D { environment in
+            body(self, environment)
+        }
     }
 }

Sources/SwiftSCAD/Environment/Operation.swift

@@ -0,0 +1,38 @@
+import Foundation
+
+public extension Environment {
+    private static let key = Environment.ValueKey(rawValue: "SwiftSCAD.Operation")
+
+    enum Operation {
+        case addition
+        case subtraction
+
+        static prefix func !(_ op: Operation) -> Operation {
+            op == .addition ? .subtraction : .addition
+        }
+    }
+
+    var operation: Operation {
+        self[Self.key] as? Operation ?? .addition
+    }
+
+    internal func invertingOperation() -> Environment {
+        setting(key: Self.key, value: !operation)
+    }
+}
+
+internal extension Geometry2D {
+    func invertingOperation() -> any Geometry2D {
+        withEnvironment { environment in
+            environment.invertingOperation()
+        }
+    }
+}
+
+internal extension Geometry3D {
+    func invertingOperation() -> any Geometry3D {
+        withEnvironment { environment in
+            environment.invertingOperation()
+        }
+    }
+}

Sources/SwiftSCAD/Operations/Boolean/Difference.swift

@@ -7,6 +7,7 @@ struct Difference3D: CoreGeometry3D {
     init(positive: any Geometry3D, negative: any Geometry3D) {
         self.positive = positive
         self.negative = negative
+            .invertingOperation()
     }
 
     func call(in environment: Environment) -> SCADCall {
@@ -46,6 +47,7 @@ struct Difference2D: CoreGeometry2D {
     init(positive: any Geometry2D, negative: any Geometry2D) {
         self.positive = positive
         self.negative = negative
+            .invertingOperation()
     }
 
     func call(in environment: Environment) -> SCADCall {

Tests/Tests/3DTests.swift

@@ -19,4 +19,31 @@ final class Geometry3DTests: XCTestCase {
             .adding {}
             .assertEqual(toFile: "empty3d")
     }
+
+    func testOperations() {
+        let testGeometry = Box([1,2,3])
+            .assertOperation(.addition)
+            .subtracting {
+                Sphere(diameter: 3)
+                    .assertOperation(.subtraction)
+                    .subtracting {
+                        Box([1,2,3])
+                            .assertOperation(.addition)
+                    }
+                    .assertOperation(.subtraction)
+            }
+            .assertOperation(.addition)
+
+        _ = testGeometry
+            .scadString(in: .defaultEnvironment)
+    }
+}
+
+extension Geometry3D {
+    func assertOperation(_ expectedOperation: Environment.Operation) -> any Geometry3D {
+        readingEnvironment { geo, environment in
+            XCTAssertEqual(environment.operation, expectedOperation)
+            geo
+        }
+    }
 }