Add Axis Rotation Support

library/options.json

@@ -356,6 +356,16 @@
     "invert_zoom": {
       "type": "bool",
       "default_value": "false"
+    },
+    "axis_lock": {
+      "axis": {
+        "type": "direction",
+        "default_value": "0,0,0"
+      },
+      "enabled": {
+        "type": "bool",
+        "default_value": "false"
+      }
     }
   }
 }

library/src/interactor_impl.cxx

@@ -915,6 +915,23 @@ interactor& interactor_impl::initCommands()
     std::bind(complNames, std::placeholders::_1,
       std::vector<std::string>{ "field", "array", "component" }));
 
+  this->addCommand("toggle_axis_lock",
+    [&](const std::vector<std::string>& args)
+    {
+      check_args(args, 1, "toggle_axis_lock");
+      const std::string val{ this->Internals->Options.getAsString("interactor.axis_lock.axis") };
+      if (args[0] == val && this->Internals->Options.interactor.axis_lock.enabled)
+      {
+        this->Internals->Options.interactor.axis_lock.enabled = false;
+      }
+      else
+      {
+        this->Internals->Options.interactor.axis_lock.axis = options::parse<f3d::direction_t>(args[0]);
+        this->Internals->Options.interactor.axis_lock.enabled = true;
+      }
+    },
+    command_documentation_t{ "toggle_axis_lock direction", "lock rotation to one direction" });
+
   this->addCommand(
     "roll_camera",
     [&](const std::vector<std::string>& args)
@@ -1363,6 +1380,9 @@ interactor& interactor_impl::initBindings()
       "Verbose level", this->Internals->VerboseLevelToString(log::getVerboseLevel()));
   };
 
+  auto docAxisTgl = [&](const std::string& doc, const std::string& val)
+  { return std::pair(doc, (this->Internals->Options.interactor.axis_lock.enabled && val == this->Internals->Options.getAsString("interactor.axis_lock.axis") ? "ON" : "OFF")); };
+
   // clang-format off
   this->addBinding({mod_t::NONE, "W"}, "cycle_animation", "Scene", docAnim, f3d::interactor::BindingType::CYCLIC);
   this->addBinding({mod_t::NONE, "C"}, "cycle_coloring field", "Scene", docField, f3d::interactor::BindingType::CYCLIC);
@@ -1391,6 +1411,9 @@ interactor& interactor_impl::initBindings()
   this->addBinding({mod_t::NONE, "O"}, "toggle model.point_sprites.enable","Scene", std::bind(docTgl, "Point sprites rendering", std::cref(opts.model.point_sprites.enable)), f3d::interactor::BindingType::TOGGLE);
   this->addBinding({mod_t::NONE, "U"}, "toggle render.background.blur.enable","Scene", std::bind(docTgl, "Blur background", std::cref(opts.render.background.blur.enable)), f3d::interactor::BindingType::TOGGLE);
   this->addBinding({mod_t::NONE, "K"}, "toggle interactor.trackball","Scene", std::bind(docTgl, "Trackball interaction", std::cref(opts.interactor.trackball)), f3d::interactor::BindingType::TOGGLE);
+  this->addBinding({mod_t::CTRL, "X"}, "toggle_axis_lock +X", "Scene", [=]() { return docAxisTgl("Toggle x axis lock", "+X"); });
+  this->addBinding({mod_t::CTRL, "Y"}, "toggle_axis_lock +Y", "Scene", [=]() { return docAxisTgl("Toggle y axis lock", "+Y"); });
+  this->addBinding({mod_t::CTRL, "Z"}, "toggle_axis_lock +Z", "Scene", [=]() { return docAxisTgl("Toggle z axis lock", "+Z"); });
   this->addBinding({mod_t::NONE, "F"}, "toggle render.hdri.ambient","Scene", std::bind(docTgl, "HDRI ambient lighting", std::cref(opts.render.hdri.ambient)), f3d::interactor::BindingType::TOGGLE);
   this->addBinding({mod_t::NONE, "J"}, "toggle render.background.skybox","Scene", std::bind(docTgl, "HDRI skybox", std::cref(opts.render.background.skybox)), f3d::interactor::BindingType::TOGGLE);
   this->addBinding({mod_t::NONE, "L"}, "increase_light_intensity", "Scene", std::bind(docDbl, "Increase lights intensity", std::cref(opts.render.light.intensity)), f3d::interactor::BindingType::NUMERICAL);

library/src/window_impl.cxx

@@ -391,6 +391,7 @@ void window_impl::UpdateDynamicOptions()
     renderer->ShowAxis(opt.ui.axis);
     renderer->SetUseTrackball(opt.interactor.trackball);
     renderer->SetInvertZoom(opt.interactor.invert_zoom);
+    renderer->SetRotationAxis(opt.interactor.axis_lock.enabled, opt.interactor.axis_lock.axis);
   }
 
   // XXX: model.point_sprites.type only has an effect on geometry scene

vtkext/private/module/vtkF3DInteractorStyle.cxx

@@ -169,23 +169,49 @@ void vtkF3DInteractorStyle::Rotate()
       this->InterpolateTemporaryUp(0.1, ren->GetUpVector(), up);
     }
 
-    // Rotate camera around the focal point about the environment's up vector
     vtkNew<vtkTransform> Transform;
-    Transform->Identity();
     const double* fp = camera->GetFocalPoint();
-    Transform->Translate(+fp[0], +fp[1], +fp[2]);
-    Transform->RotateWXYZ(rxf, ren->GetUpVector());
-    Transform->Translate(-fp[0], -fp[1], -fp[2]);
-    Transform->TransformPoint(camera->GetPosition(), camera->GetPosition());
-
-    camera->SetViewUp(up);
-
-    // Clamp parameter to `camera->Elevation()` to maintain -90 < elevation < +90
-    constexpr double maxAbsElevation = 90 - 1e-10;
-    const double elevation = vtkMath::DegreesFromRadians(
-      vtkMath::AngleBetweenVectors(ren->GetUpVector(), camera->GetDirectionOfProjection()) -
-      vtkMath::Pi() / 2);
-    camera->Elevation(std::clamp(ryf, -maxAbsElevation - elevation, +maxAbsElevation - elevation));
+    double newPos[3];
+    if (ren->GetUseRotationAxis())
+    {
+
+      // pick whichever mouse component is larger
+      bool use_dx = std::abs(dx) > std::abs(dy);
+      double delta = 20.0 * this->MotionFactor * (use_dx ? dx * 1.0 / size[0] : dy * -1.0 / size[1]);
+
+      Transform->Identity();
+      Transform->Translate(+fp[0], +fp[1], +fp[2]);
+      Transform->RotateWXYZ(delta, ren->GetRotationAxis());
+      Transform->Translate(-fp[0], -fp[1], -fp[2]);
+
+      Transform->TransformPoint(camera->GetPosition(), newPos);
+      camera->SetPosition(newPos);
+
+      double newViewUp[3];
+      Transform->TransformVector(camera->GetViewUp(), newViewUp);
+      camera->SetViewUp(newViewUp);
+    }
+    else
+    {
+      // Rotate camera around the focal point about the environment's up vector
+      Transform->Identity();
+      Transform->Translate(+fp[0], +fp[1], +fp[2]);
+      Transform->RotateWXYZ(rxf, ren->GetUpVector());
+      Transform->Translate(-fp[0], -fp[1], -fp[2]);
+
+      Transform->TransformPoint(camera->GetPosition(), newPos);
+      camera->SetPosition(newPos);
+
+      // Clamp parameter to `camera->Elevation()` to maintain -90 < elevation < +90
+      constexpr double maxAbsElevation = 90 - 1e-10;
+      const double elevation = vtkMath::DegreesFromRadians(
+        vtkMath::AngleBetweenVectors(ren->GetUpVector(), camera->GetDirectionOfProjection()) -
+        vtkMath::Pi() / 2);
+      camera->Elevation(
+        std::clamp(ryf, -maxAbsElevation - elevation, +maxAbsElevation - elevation));
+
+      camera->SetViewUp(up);
+    }
 
     camera->OrthogonalizeViewUp();
   }

vtkext/private/module/vtkF3DRenderer.cxx

@@ -1743,6 +1743,25 @@ void vtkF3DRenderer::SetUseTrackball(bool use)
   }
 }
 
+//----------------------------------------------------------------------------
+void vtkF3DRenderer::SetRotationAxis(bool use, const std::vector<double>& axis)
+{
+  std::array<double, 3> prev = { this->RotationAxis[0], this->RotationAxis[1],
+    this->RotationAxis[2] };
+  std::array<double, 3> curr = { axis[0], axis[1], axis[2] };
+
+  if (use != this->UseRotationAxis || curr != prev)
+  {
+    this->UseRotationAxis = use;
+
+    this->RotationAxis[0] = axis[0];
+    this->RotationAxis[1] = axis[1];
+    this->RotationAxis[2] = axis[2];
+
+    this->CheatSheetConfigured = false;
+  }
+}
+
 //----------------------------------------------------------------------------
 void vtkF3DRenderer::UpdateActors()
 {

vtkext/private/module/vtkF3DRenderer.h

@@ -131,6 +131,13 @@ class vtkF3DRenderer : public vtkOpenGLRenderer
   ///@}
 
   /**
+   * Set/Get RotationAxis
+   */
+  void SetRotationAxis(bool use, const std::vector<double>& axis);  
+  vtkGetMacro(UseRotationAxis, bool);
+  vtkGetVector3Macro(RotationAxis, double);
+
+   /**
    * Reimplemented to configure:
    *  - ActorsProperties
    *  - Timer
@@ -580,6 +587,8 @@ class vtkF3DRenderer : public vtkOpenGLRenderer
   std::optional<bool> UseOrthographicProjection = false;
   bool UseTrackball = false;
   bool InvertZoom = false;
+  bool UseRotationAxis = false;
+  double RotationAxis[3] = { 0.0, 0.0, 0.0 };
 
   int RaytracingSamples = 0;
   double UpVector[3] = { 0.0, 1.0, 0.0 };