cs;
mapper->SetInputConnection(cs->GetOutputPort());
renderer->ResetCamera();
```
So, this worked and I was able to get a cube (whole code at: [Win32\_OpenGL/main.cpp at vtk · Chahat08/Win32\_OpenGL · GitHub](https://github.com/Chahat08/Win32_OpenGL/blob/vtk/main.cpp)). However, when I tried extending the same to volume rendering, it didn’t work:
` renderer->AddViewProp(volume);`
For full context, this is the MedicalDemo4 volume rendering example from the VTK examples website ([https://examples.vtk.org/site/Cxx/Medical/MedicalDemo4/](https://examples.vtk.org/site/Cxx/Medical/MedicalDemo4/)). My full code for testing volume rendering is at [Win32\_OpenGL/main.cpp at volume\_rendering · Chahat08/Win32\_OpenGL · GitHub](https://github.com/Chahat08/Win32_OpenGL/blob/volume_rendering/main.cpp).
I’m using OpenGL 3.3 with custom shaders and Win32 for window creation and management.
---
### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [August 22, 2024, 2:11pm UTC](https://discourse.vtk.org/t/unable-to-do-volume-rendering-on-external-vtk-render-window/14459/2 "2024-08-22T14:11:40Z")
Hello @CK008
Thank you for sharing the code.
> I’m using OpenGL 3.3 with custom shaders and Win32 for window creation and management.
This maybe the problem.
I see that you’re using `gladLoadGL`. Can you regenerate the glad.c files to target OpenGL 4.5 instead?
---
### Author:  [@CK008](https://discourse.vtk.org/u/CK008)
#### Post date: [August 22, 2024, 3:31pm UTC](https://discourse.vtk.org/t/unable-to-do-volume-rendering-on-external-vtk-render-window/14459/3 "2024-08-22T15:31:40Z")
Hi @jaswantp , thank you for the reply.
I tried with OpenGL 4.5 and still am unable to render the volume.
---
### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [August 22, 2024, 4:01pm UTC](https://discourse.vtk.org/t/unable-to-do-volume-rendering-on-external-vtk-render-window/14459/4 "2024-08-22T16:01:26Z")
Probably because you’re creating a 1.1 opengl context using `wglCreateContext`. Instead you might have to use wgl extensions `wglChoosePixelFormatARB` and `wglCreateContextAttribsARB` like done in `vtkWin32OpenGLRenderWindow` [https://gitlab.kitware.com/vtk/vtk/-/blob/master/Rendering/OpenGL2/vtkWin32OpenGLRenderWindow.cxx#L577](https://gitlab.kitware.com/vtk/vtk/-/blob/master/Rendering/OpenGL2/vtkWin32OpenGLRenderWindow.cxx#L577).
For the extensions, you can generate `wgl.h` and `wgl.c` as well from glad site and call `gladLoaderLoadWGL` before `gladLoadGL`.
---
### Author:  [@CK008](https://discourse.vtk.org/u/CK008)
#### Post date: [August 28, 2024, 6:20pm UTC](https://discourse.vtk.org/t/unable-to-do-volume-rendering-on-external-vtk-render-window/14459/5 "2024-08-28T18:20:17Z")
Hey, I tried again, this time creating the win32 app as you suggested. Again, I was able to get the cube to render but the volume still does not show up.
It would definitely help if I can get some example or tutorial where volume rendering is done in an external opengl context.
---
### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [August 28, 2024, 6:23pm UTC](https://discourse.vtk.org/t/unable-to-do-volume-rendering-on-external-vtk-render-window/14459/6 "2024-08-28T18:23:49Z")
Do you see any shader errors?
Otherwise, it could be that the camera is incorrectly configured. Can you try `renderer->ResetCamera()` and `renderer->ResetCameraClippingRange()`?
---
### Author:  [@CK008](https://discourse.vtk.org/u/CK008)
#### Post date: [August 28, 2024, 6:30pm UTC](https://discourse.vtk.org/t/unable-to-do-volume-rendering-on-external-vtk-render-window/14459/7 "2024-08-28T18:30:24Z")
I tried them both, it doesn’t work. And there’s no errors either.
So, the interesting thing is that I used RenderDoc to analyse the buffer contents of my application. For the cube example, I can clearly see the geometry being passed to the vertex shader.
However, I can not see anything being passed to the shaders for the volume rendering example. And it’s definitely don’t the case that the volume is not being read or parsed correctly, because I can see the volume bounds using `volume->GetBounds()` and they are correct.
---
### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [August 28, 2024, 6:40pm UTC](https://discourse.vtk.org/t/unable-to-do-volume-rendering-on-external-vtk-render-window/14459/8 "2024-08-28T18:40:12Z")
> [@CK008](#):
>
> However, I can not see anything being passed to the shaders for the volume rendering example.
Could you use `vtkSmartVolumeMapper` instead of `vtkFixedPointVolumeRayCastMapper`? The fixed point mapper is software based, it doesn’t use OpenGL.
---
### Author:  [@CK008](https://discourse.vtk.org/u/CK008)
#### Post date: [August 28, 2024, 7:14pm UTC](https://discourse.vtk.org/t/unable-to-do-volume-rendering-on-external-vtk-render-window/14459/9 "2024-08-28T19:14:44Z")
Is replacing `vtkNew volumeMapper;` with `vtkNew volumeMapper;` sufficient? Just doing that is still not rendering the volume.
I’m new to VTK so am unsure if I’m doing things the right way. The image from this post is the only clue I have that makes it seem like volume rendering in an external context is even possible. But, since I can’t find any examples demonstrating it, I’m feeling really struck at this point.
[https://www.kitware.com/new-in-vtk-rendering-in-external-immersive-environments/](https://www.kitware.com/new-in-vtk-rendering-in-external-immersive-environments/)
---
### Author:  [@sankhesh](https://discourse.vtk.org/u/sankhesh)
#### Post date: [August 28, 2024, 7:38pm UTC](https://discourse.vtk.org/t/unable-to-do-volume-rendering-on-external-vtk-render-window/14459/10 "2024-08-28T19:38:27Z")
@CK008 Are you getting any errors? Or is it just that you’re not seeing any rendering? If so, my guess is that your camera parameters are clipping the volume away. Could you make sure that your OpenGL camera frustum is set up properly to encapsulate the volume bounds?
Switching to `vtkSmartVolumeMapper` is definitely the right way to go forward.