From 8dd3e908961654265fcf23e6fea2a77d435ed61e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stefan=20Tr=C3=B6ger?= <stefantroeger@gmx.net>
Date: Thu, 8 May 2025 19:30:01 +0200
Subject: [PATCH] FEM: port DataAlongLine filter to use arc length. This makes
 it easier for the new data extraction to also plot data over line length.

---
 src/Mod/Fem/App/FemPostFilter.cpp | 17 +++++++----------
 src/Mod/Fem/App/FemPostFilter.h   |  2 ++
 2 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/src/Mod/Fem/App/FemPostFilter.cpp b/src/Mod/Fem/App/FemPostFilter.cpp
index d7d054f083..79da85c5a1 100644
--- a/src/Mod/Fem/App/FemPostFilter.cpp
+++ b/src/Mod/Fem/App/FemPostFilter.cpp
@@ -382,18 +382,21 @@ FemPostDataAlongLineFilter::FemPostDataAlongLineFilter()
     m_line->SetPoint2(vec2.x, vec2.y, vec2.z);
     m_line->SetResolution(Resolution.getValue());
 
+    m_arclength = vtkSmartPointer<vtkAppendArcLength>::New();
+    m_arclength->SetInputConnection(m_line->GetOutputPort(0));
+
 
     auto passthrough = vtkSmartPointer<vtkPassThrough>::New();
     m_probe = vtkSmartPointer<vtkProbeFilter>::New();
     m_probe->SetSourceConnection(passthrough->GetOutputPort(0));
-    m_probe->SetInputConnection(m_line->GetOutputPort());
-    m_probe->SetValidPointMaskArrayName("ValidPointArray");
+    m_probe->SetInputConnection(m_arclength->GetOutputPort());
     m_probe->SetPassPointArrays(1);
     m_probe->SetPassCellArrays(1);
     m_probe->ComputeToleranceOff();
     m_probe->SetTolerance(0.01);
 
     clip.source = passthrough;
+    clip.algorithmStorage.push_back(m_arclength);
     clip.target = m_probe;
 
     addFilterPipeline(clip, "DataAlongLine");
@@ -488,12 +491,7 @@ void FemPostDataAlongLineFilter::GetAxisData()
         return;
     }
 
-    vtkDataArray* tcoords = dset->GetPointData()->GetTCoords("Texture Coordinates");
-
-    const Base::Vector3d& vec1 = Point1.getValue();
-    const Base::Vector3d& vec2 = Point2.getValue();
-    const Base::Vector3d diff = vec1 - vec2;
-    double Len = diff.Length();
+    vtkDataArray* alength = dset->GetPointData()->GetArray("arc_length");
 
     for (vtkIdType i = 0; i < dset->GetNumberOfPoints(); ++i) {
         double value = 0;
@@ -517,8 +515,7 @@ void FemPostDataAlongLineFilter::GetAxisData()
         }
 
         values.push_back(value);
-        double tcoord = tcoords->GetComponent(i, 0);
-        coords.push_back(tcoord * Len);
+        coords.push_back(alength->GetTuple1(i));
     }
 
     YAxisData.setValues(values);
diff --git a/src/Mod/Fem/App/FemPostFilter.h b/src/Mod/Fem/App/FemPostFilter.h
index 273bd63c0f..38499d01d3 100644
--- a/src/Mod/Fem/App/FemPostFilter.h
+++ b/src/Mod/Fem/App/FemPostFilter.h
@@ -32,6 +32,7 @@
 #include <vtkLineSource.h>
 #include <vtkPointSource.h>
 #include <vtkProbeFilter.h>
+#include <vtkAppendArcLength.h>
 #include <vtkSmartPointer.h>
 #include <vtkTableBasedClipDataSet.h>
 #include <vtkVectorNorm.h>
@@ -181,6 +182,7 @@ protected:
 
 private:
     vtkSmartPointer<vtkLineSource> m_line;
+    vtkSmartPointer<vtkAppendArcLength> m_arclength;
     vtkSmartPointer<vtkProbeFilter> m_probe;
 };