feat: disable camera spin/inertia by introducing a custom interactor style.r

src/Vtk/uLibVtkViewer.cpp

@@ -37,9 +37,29 @@
 #include <vtkTextProperty.h>
 #include <vtkAxesActor.h>
 #include <vtkCamera.h>
+#include <vtkInteractorStyleTrackballCamera.h>
+#include <vtkObjectFactory.h>
 
 #include "uLibVtkViewer.h"
 
+// Custom interactor style: disables spin/inertia so the scene only
+// rotates while the mouse is actively being moved with the button held.
+class vtkInteractorStyleNoSpin : public vtkInteractorStyleTrackballCamera
+{
+public:
+    static vtkInteractorStyleNoSpin *New();
+    vtkTypeMacro(vtkInteractorStyleNoSpin, vtkInteractorStyleTrackballCamera);
+
+    // Override: when the left button is released, immediately stop any
+    // ongoing motion (rotation/spin) so no momentum is carried over.
+    void OnLeftButtonUp() override
+    {
+        this->StopState();
+        vtkInteractorStyleTrackballCamera::OnLeftButtonUp();
+    }
+};
+vtkStandardNewMacro(vtkInteractorStyleNoSpin);
+
 namespace uLib {
 namespace Vtk {
 
@@ -75,6 +95,11 @@ void Viewer::InstallPipe()
             vtkSmartPointer<vtkRenderWindowInteractor>::New();
     renderWindowInteractor->SetRenderWindow(m_RenderWindow);
 
+    // Use a custom style with no spin/inertia
+    vtkSmartPointer<vtkInteractorStyleNoSpin> style =
+            vtkSmartPointer<vtkInteractorStyleNoSpin>::New();
+    renderWindowInteractor->SetInteractorStyle(style);
+
     // annotation //
     m_Annotation->GetTextProperty()->SetColor(1,1,1);
     m_Annotation->GetTextProperty()->SetFontFamilyToArial();