fix lazy collider (#1540)

* fix

* add test

src/lazy_collider.cpp

@@ -23,6 +23,7 @@ LazyCollider::LazyCollider(LeafData&& leafData)
 LazyCollider::LazyCollider(std::shared_ptr<const LazyCollider> base,
                            const mat3x4& transform) {
   DEBUG_ASSERT(base != nullptr, logicErr, "invalid base ptr");
+  // keeps as an optimization
   mat3x4 composed = transform;
   // attempt to unwrap one level, if the base is also a transformed collider
   // we do not unwrap if the base has updatedLeafBox
@@ -103,9 +104,10 @@ const LazyCollider::Built& LazyCollider::EnsureBuilt() const {
 
   if (base_) {
     const Built& baseBuilt = base_->base->EnsureBuilt();
-    // no need to propagate transform from built, we already computed the
-    // composed transform in the constructor
-    built_ = {baseBuilt.collider, base_->transform};
+    // propagate transform when collider was built after construct
+    mat3x4 composed = base_->transform;
+    if (baseBuilt.transform) composed = composed * Mat4(*baseBuilt.transform);
+    built_ = {baseBuilt.collider, composed};
     if (base_->updatedLeafBox) {
       auto leafBox = std::move(base_->updatedLeafBox.value());
       base_ = std::nullopt;

test/boolean_complex_test.cpp

@@ -1519,6 +1519,24 @@ TEST(BooleanComplex, HullMask) {
   MeshGL mesh = ret.GetMeshGL();
 }
 
+TEST(BooleanComplex, LazyCollider) {
+  Manifold ele1 = Manifold::Cylinder(50, 50);
+  Manifold ele2 = Manifold::Cylinder(60, 30);
+  Manifold ele3 = Manifold::Cylinder(60, 40).Mirror(vec3{0, 0, 1});
+
+  Manifold ele4 = (ele1 + ele2).Mirror(vec3{0, 0, 1});
+
+  EXPECT_NEAR(ele4.Volume(), 418839, 1);
+
+  Manifold r1 = ele4 - ele2.Translate(vec3{0, 0, -20});
+
+  EXPECT_NEAR(r1.Volume(), 362577, 1);
+
+  Manifold r2 = ele4.Translate(vec3{0, 0, 1}) - ele3;
+
+  EXPECT_NEAR(r2.Volume(), 145656, 1);
+}
+
 #ifdef MANIFOLD_DEBUG
 TEST(BooleanComplex, OffsetTriangulationFailure) {
   ManifoldParamGuard guard;