UI: Add proper delta time configuration

library/src/interactor_impl.cxx

@@ -11,6 +11,7 @@
 #include "vtkF3DInteractorStyle.h"
 #include "vtkF3DRenderer.h"
 #include "vtkF3DUIObserver.h"
+#include "vtkF3DUIActor.h"
 
 #include <vtkCallbackCommand.h>
 #include <vtkCellPicker.h>
@@ -1136,6 +1137,11 @@ void interactor_impl::start(double loopTime, std::function<void()> userCallBack)
     this->Internals->EventLoopUserCallBack = std::move(userCallBack);
   }
 
+  vtkRenderWindow* renWin = this->Internals->Window.GetRenderWindow();
+  vtkF3DRenderer* ren =
+    vtkF3DRenderer::SafeDownCast(renWin->GetRenderers()->GetFirstRenderer());
+  ren->SetUIDeltaTime(loopTime);
+
   this->Internals->AnimationManager->SetInteractorEventLoopTime(loopTime);
   this->Internals->EventLoopTimerId = this->createTimerCallBack(loopTime, [this]() { this->EventLoop(); });
   this->Internals->VTKInteractor->Start();

vtkext/private/module/vtkF3DImguiActor.cxx

@@ -471,3 +471,10 @@ void vtkF3DImguiActor::EndFrame(vtkOpenGLRenderWindow* renWin)
   ImGui::Render();
   this->Pimpl->RenderDrawData(renWin, ImGui::GetDrawData());
 }
+
+//----------------------------------------------------------------------------
+void vtkF3DImguiActor::SetDeltaTime(double time)
+{
+  ImGuiIO& io = ImGui::GetIO();
+  io.DeltaTime = time / 1000;
+}

vtkext/private/module/vtkF3DImguiActor.h

@@ -31,6 +31,11 @@ class vtkF3DImguiActor : public vtkF3DUIActor
    */
   void ReleaseGraphicsResources(vtkWindow* w) override;
 
+  /**
+   * Set imgui::DeltaTime, with time in ms
+   */
+  void SetDeltaTime(double time) override;
+
 protected:
   vtkF3DImguiActor();
   ~vtkF3DImguiActor() override;

vtkext/private/module/vtkF3DRenderer.cxx

@@ -2621,3 +2621,9 @@ void vtkF3DRenderer::SetCheatSheetConfigured(bool flag)
 {
   this->CheatSheetConfigured = flag;
 }
+
+//----------------------------------------------------------------------------
+void vtkF3DRenderer::SetUIDeltaTime(double time)
+{
+  this->UIActor->SetDeltaTime(time);
+}

vtkext/private/module/vtkF3DRenderer.h

@@ -371,6 +371,11 @@ class vtkF3DRenderer : public vtkOpenGLRenderer
    */
   void SetCheatSheetConfigured(bool flag);
 
+  /**
+   * Set the UI delta time (time between frame being rendered) in ms
+   */
+  void SetUIDeltaTime(double time);
+
 private:
   vtkF3DRenderer();
   ~vtkF3DRenderer() override;

vtkext/private/module/vtkF3DUIActor.h

@@ -91,6 +91,11 @@ class vtkF3DUIActor : public vtkProp
    */
   int RenderOverlay(vtkViewport* vp) override;
 
+  /**
+   * Set the delta time (time between UI frames) in ms
+   */
+  virtual void SetDeltaTime(double time) {}
+
 protected:
   vtkF3DUIActor();
   ~vtkF3DUIActor() override;