Backported a fix from Clipper 6.4.2 for the issue that Clipper Z coordinated has incorrect value because ZFillFunction wasn't called in all cases (https://sourceforge.net/p/polyclipping/bugs/160/). Also, this issue led to duplicity vertices with the same XY coordinates but differ in Z coordinates.

3 files changed, 53 insertions, 0 deletions

diff --git a/src/clipper/clipper.cpp b/src/clipper/clipper.cpp
index 84d68b1e6..84109398a 100644
--- a/src/clipper/clipper.cpp
+++ b/src/clipper/clipper.cpp
@@ -2290,6 +2290,12 @@ void Clipper::ProcessHorizontal(TEdge *horzEdge)
 
     if (horzEdge->OutIdx >= 0 && !IsOpen)  //note: may be done multiple times
 		{
+#ifdef CLIPPERLIB_USE_XYZ
+            if (dir == dLeftToRight)
+                SetZ(e->Curr, *horzEdge, *e);
+            else
+                SetZ(e->Curr, *e, *horzEdge);
+#endif
             op1 = AddOutPt(horzEdge, e->Curr);
 			TEdge* eNextHorz = m_SortedEdges;
 			while (eNextHorz)
@@ -2614,6 +2620,9 @@ void Clipper::ProcessEdgesAtTopOfScanbeam(const cInt topY)
       {
         e->Curr.x() = TopX( *e, topY );
         e->Curr.y() = topY;
+#ifdef CLIPPERLIB_USE_XYZ
+        e->Curr.z() = topY == e->Top.y() ? e->Top.z() : (topY == e->Bot.y() ? e->Bot.z() : 0);
+#endif
       }
 
       //When StrictlySimple and 'e' is being touched by another edge, then
diff --git a/tests/fff_print/CMakeLists.txt b/tests/fff_print/CMakeLists.txt
index 4e8821287..0b3b920b9 100644
--- a/tests/fff_print/CMakeLists.txt
+++ b/tests/fff_print/CMakeLists.txt
@@ -4,6 +4,7 @@ add_executable(${_TEST_NAME}_tests
 	test_avoid_crossing_perimeters.cpp
 	test_bridges.cpp
 	test_cooling.cpp
+	test_clipper.cpp
 	test_custom_gcode.cpp
 	test_data.cpp
 	test_data.hpp
diff --git a/tests/fff_print/test_clipper.cpp b/tests/fff_print/test_clipper.cpp
new file mode 100644
index 000000000..dc49ce0f1
--- /dev/null
+++ b/tests/fff_print/test_clipper.cpp
@@ -0,0 +1,43 @@
+#include <catch2/catch.hpp>
+
+#include "test_data.hpp"
+#include "clipper/clipper_z.hpp"
+
+using namespace Slic3r;
+
+// Test case for an issue with duplicity vertices (same XY coordinates but differ in Z coordinates) in Clipper 6.2.9,
+// (related to https://sourceforge.net/p/polyclipping/bugs/160/) that was fixed in Clipper 6.4.2.
+SCENARIO("Clipper Z", "[ClipperZ]")
+{
+    ClipperLib_Z::Path subject;
+
+    subject.emplace_back(-2000, -1000, 10);
+    subject.emplace_back(-2000,  1000, 10);
+    subject.emplace_back( 2000,  1000, 10);
+    subject.emplace_back( 2000, -1000, 10);
+
+    ClipperLib_Z::Path clip;
+    clip.emplace_back(-1000, -2000, -5);
+    clip.emplace_back(-1000,  2000, -5);
+    clip.emplace_back( 1000,  2000, -5);
+    clip.emplace_back( 1000, -2000, -5);
+
+    ClipperLib_Z::Clipper clipper;
+    clipper.ZFillFunction([](const ClipperLib_Z::IntPoint &e1bot, const ClipperLib_Z::IntPoint &e1top, const ClipperLib_Z::IntPoint &e2bot,
+                             const ClipperLib_Z::IntPoint &e2top, ClipperLib_Z::IntPoint &pt) {
+        pt.z() = 1;
+    });
+
+    clipper.AddPath(subject, ClipperLib_Z::ptSubject, false);
+    clipper.AddPath(clip, ClipperLib_Z::ptClip, true);
+
+    ClipperLib_Z::PolyTree polytree;
+    ClipperLib_Z::Paths    paths;
+    clipper.Execute(ClipperLib_Z::ctIntersection, polytree, ClipperLib_Z::pftNonZero, ClipperLib_Z::pftNonZero);
+    ClipperLib_Z::PolyTreeToPaths(polytree, paths);
+
+    REQUIRE(paths.size() == 1);
+    REQUIRE(paths.front().size() == 2);
+    for (const ClipperLib_Z::IntPoint &pt : paths.front())
+        REQUIRE(pt.z() == 1);
+}
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