vtk+DearImGui integration through vtkGenericOpenGLRenderWindow

[phcerdan (Pablo Hernandez Cerdan)]

Hi @jaswantp,
I just tested it in Linux, It compiles fine.
Tested using two versions of VTK 9:

• commit 48f8d11f2b79e552fc25d1ab407f9881b51dce0a (15 April 2021)
• VTK 9 master (1 Jun 2021).

In both cases, the executable test_imgui_vtk starts fine, but when interacting with the VTK rendering, an assertion from imgui pops up:

test_imgui_vtk: vtkDearImGUIInjector/src/imgui/imgui.cpp:7154: void ImGui::ErrorCheckNewFrameSanityChecks(): Assertion `(g.IO.DeltaTime > 0.0f || g.FrameCount == 0) && "Need a positive DeltaTime!"' failed.
[1]    3015218 abort (core dumped)  ./test_imgui_vtk

When building in Release mode, once I click and start interacting with the VTK scene, I am not able to keep interacting with it (see gif).

There are no OpenGL errors reported with VTK_REPORT_OPENGL_ERRORS and VTK_REPORT_OPENGL_ERRORS_IN_RELEASE_BUILD both ON.

@jaswantp

• requires no 3rd party windowing system!
• No need to render to texture! It uses the same render buffer that VTK will use as a read-buffer and blit into display buffer. This blit occurs in Frame call.

Looking good though!