# How to integrate VTK with OpenGL?
**URL:** https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526
**Category:** Support
**Tags:** code
**Created:** [May 23, 2023, 3:37pm UTC](https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526 "2023-05-23T15:37:08Z")
**Posts on this page:** 17
**Page:** 1
### Author:  [@fghoussen](https://discourse.vtk.org/u/fghoussen)
#### Post date: [May 23, 2023, 3:37pm UTC](https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526/1 "2023-05-23T15:37:09Z")
How to integrate VTK with OpenGL?
I have a regular VTK pipeline that works OK: I use a vtkPolyData, set it as input to a vtkXXXFilter, use a vtkPolyDataMapper, and render it in a vtkRenderWindow (using a vtkRenderer). All is OK: my scene is rendered over a white background! I do not use any OpenGL-related classes so far (or, say, I’am not sure what is used in back-end to do the rendering).
Now I need to make this VTK pipeline interact with GLFW/OpenGL: I need to retrieve a GLFWwindow consistent with OpenGL.
Replacing vtkRenderWindow with vtkOpenGLRenderWindow doesn’t compile: my understanding is that this class is not meant to be used directly. **Question 1** : is this correct?
Replacing vtkRenderWindow with vtkGenericOpenGLRenderWindow compiles but crashes:
```auto
(gdb) bt
#0 0x0000000000000000 in ?? ()
#1 0x00007ffff7c1dae9 in vtkOpenGLState::vtkglBlendFuncSeparate (this=0x5555555ac2e0, val1=770, val2=771, val3=1, val4=771)
at /home/fhoussen/Downloads/VTK-9.2.6/Rendering/OpenGL2/vtkOpenGLState.cxx:873
#2 0x00007ffff7be901a in vtkOpenGLRenderWindow::Start (this=0x5555555abad0) at /home/fhoussen/Downloads/VTK-9.2.6/Rendering/OpenGL2/vtkOpenGLRenderWindow.cxx:1291
#3 0x00007ffff75ecfa1 in vtkXRenderWindowInteractor::Initialize (this=0x5555555add90) at /home/fhoussen/Downloads/VTK-9.2.6/Rendering/UI/vtkXRenderWindowInteractor.cxx:347
#1 0x00007ffff7c1dae9 in vtkOpenGLState::vtkglBlendFuncSeparate (this=0x5555555ac2e0, val1=770, val2=771, val3=1, val4=771)
at /home/fhoussen/Downloads/VTK-9.2.6/Rendering/OpenGL2/vtkOpenGLState.cxx:873
873 ::glBlendFuncSeparate(val1, val2, val3, val4);
(gdb) l
868 {
869 cs.BlendFunc[0] = val1;
870 cs.BlendFunc[1] = val2;
871 cs.BlendFunc[2] = val3;
872 cs.BlendFunc[3] = val4;
873 ::glBlendFuncSeparate(val1, val2, val3, val4);
874 }
875 vtkCheckOpenGLErrorsWithStack("glBlendFuncSeparate");
876 }
```
**Question 2** : how to fix/avoid this? Seems the crash occurs in ::glBlendFuncSeparate
So I tried to replace vtkRenderWindow with vtkXOpenGLRenderWindow (running on unix - I guess vtkWin32OpenGLRenderWindow is meant to be used on windows): the code compiles and run with no crash. **Question 3** : is there a class vtkXXXRenderWindow that can be used on both unix/windows/macOS? (I hoped this could be vtkGenericOpenGLRenderWindow)
With vtkXOpenGLRenderWindow, the code compiles but I get a black screen with no data rendered. **Question 4** : what is missing to get the same scene as I had initially but with OpenGL?
---
### Author:  [@mwestphal](https://discourse.vtk.org/u/mwestphal)
#### Post date: [May 23, 2023, 3:45pm UTC](https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526/2 "2023-05-23T15:45:30Z")
Hi @fghoussen
You need to use the vtkExternalOpenGLRenderWindow
---
### Author:  [@fghoussen](https://discourse.vtk.org/u/fghoussen)
#### Post date: [May 23, 2023, 3:46pm UTC](https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526/3 "2023-05-23T15:46:27Z")
OK, does vtkExternalOpenGLRenderWindow works on unix/window/macOS?
@mwestphal I have a compilation error: fatal error: vtkExternalOpenGLRenderWindow.h: No such file or directory
Is it necesseray to build VTK from source? If yes, are there options to set at configure time?
---
### Author:  [@fghoussen](https://discourse.vtk.org/u/fghoussen)
#### Post date: [May 24, 2023, 1:24pm UTC](https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526/4 "2023-05-24T13:24:03Z")
Using vtkExternalOpenGLRenderWindow, I get a crash. @mwestphal: any clue?
```auto
(gdb) bt
#0 0x0000000000000000 in ?? ()
#1 0x00007ffff7b2c289 in vtkOpenGLFramebufferObject::CreateFBO (this=0x5555555b9080) at /home/fhoussen/Downloads/VTK/VTK-9.2.6/Rendering/OpenGL2/vtkOpenGLFramebufferObject.cxx:354
#2 0x00007ffff7b2e81a in vtkOpenGLFramebufferObject::Bind (this=0x5555555b9080, mode=36160) at /home/fhoussen/Downloads/VTK/VTK-9.2.6/Rendering/OpenGL2/vtkOpenGLFramebufferObject.cxx:740
#3 0x00007ffff7b2e619 in vtkOpenGLFramebufferObject::Bind (this=0x5555555b9080) at /home/fhoussen/Downloads/VTK/VTK-9.2.6/Rendering/OpenGL2/vtkOpenGLFramebufferObject.cxx:729
#4 0x00007ffff7b33559 in vtkOpenGLFramebufferObject::PopulateFramebuffer (this=0x5555555b9080, width=300, height=32767, useTextures=true, numberOfColorAttachments=1, colorDataType=3,
wantDepthAttachment=true, depthBitplanes=32, multisamples=0, wantStencilAttachment=false) at /home/fhoussen/Downloads/VTK/VTK-9.2.6/Rendering/OpenGL2/vtkOpenGLFramebufferObject.cxx:1502
#5 0x00007ffff7bebe3b in vtkOpenGLRenderWindow::CreateFramebuffers (this=0x5555555b7be0, width=300, height=32767)
at /home/fhoussen/Downloads/VTK/VTK-9.2.6/Rendering/OpenGL2/vtkOpenGLRenderWindow.cxx:2105
#6 0x00007ffff7f209bc in vtkExternalOpenGLRenderWindow::Start (this=0x5555555b7be0) at /home/fhoussen/Downloads/VTK/VTK-9.2.6/Rendering/External/vtkExternalOpenGLRenderWindow.cxx:57
#7 0x00007ffff7e2cfa1 in vtkXRenderWindowInteractor::Initialize (this=0x5555555ba520) at /home/fhoussen/Downloads/VTK/VTK-9.2.6/Rendering/UI/vtkXRenderWindowInteractor.cxx:347
#8 0x0000555555557b9e in createScene(unsigned int const&, bool const&) ()
(gdb) up
#1 0x00007ffff7b2c289 in vtkOpenGLFramebufferObject::CreateFBO (this=0x5555555b9080) at /home/fhoussen/Downloads/VTK/VTK-9.2.6/Rendering/OpenGL2/vtkOpenGLFramebufferObject.cxx:354
354 glGenFramebuffers(1, &temp);
(gdb) l
349 if (!this->FBOIndex)
350 {
351 this->ResourceCallback->RegisterGraphicsResources(this->Context);
352 this->FBOIndex = 0;
353 GLuint temp;
354 glGenFramebuffers(1, &temp);
355 vtkOpenGLCheckErrorMacro("failed at glGenFramebuffers");
356 this->FBOIndex = temp;
357 }
358 }
```
---
### Author:  [@Jens\_Munk\_Hansen](https://discourse.vtk.org/u/Jens_Munk_Hansen)
#### Post date: [May 24, 2023, 7:17pm UTC](https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526/5 "2023-05-24T19:17:04Z")
You need to build VTK with vtkRenderingExternal. I know there is a GLUT example in the VTK source tree.
---
### Author:  [@fghoussen](https://discourse.vtk.org/u/fghoussen)
#### Post date: [May 25, 2023, 7:38am UTC](https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526/6 "2023-05-25T07:38:00Z")
> [@Jens\_Munk\_Hansen](#):
>
> I know there is a GLUT
@Jens_Munk_Hansen: I did! 🙂
Here is the cmake command I used to build VTK from source `cmake -DVTK_GROUP_ENABLE_Rendering=YES -DVTK_MODULE_ENABLE_VTK_RenderingExternal=YES ..`: is there something missing here?
Also I use `find_package(VTK COMPONENT RenderingCore RenderingExternal)` to compile/link my code base to VTK.
Do you remember where is the GLUT example? Didn’t find it, will re-check…
---
### Author:  [@fghoussen](https://discourse.vtk.org/u/fghoussen)
#### Post date: [May 25, 2023, 12:14pm UTC](https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526/7 "2023-05-25T12:14:59Z")
> Do you remember where is the GLUT example? Didn’t find it, will re-check…
Rendering/External/Testing/Cxx/TestGLUTRenderWindow.cxx
---
### Author:  [@fghoussen](https://discourse.vtk.org/u/fghoussen)
#### Post date: [May 25, 2023, 1:48pm UTC](https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526/8 "2023-05-25T13:48:56Z")
> [@Jens\_Munk\_Hansen](#):
>
> VTK with vtkRenderingExternal. I know there is a GLUT example in the VTK source tree.
I took inspiration from the VTK GLUT example. Basically, I managed to add:
```auto
// Initialize GLFW.
glfwInit();
GLFWwindow * window = glfwCreateWindow(800, 600, "window", NULL, NULL);
if (!window) {
std::cerr << "Error: can't create OpenGL window" << std::endl;
return 1;
}
glfwMakeContextCurrent(window);
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
```
And
```auto
// Terminate GLFW.
glfwTerminate();
```
Before and after the creation of the VTK pipeline
Unfortunately, I still get the same crash in `glGenFramebuffers` under `vtkOpenGLFramebufferObject::CreateFBO`?!.. @Jens_Munk_Hansen: any clue?
---
### Author:  [@Jens\_Munk\_Hansen](https://discourse.vtk.org/u/Jens_Munk_Hansen)
#### Post date: [May 25, 2023, 5:31pm UTC](https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526/9 "2023-05-25T17:31:55Z")
Try the GLUT as is. Did you very OpenGL using another application?
---
### Author:  [@fghoussen](https://discourse.vtk.org/u/fghoussen)
#### Post date: [May 30, 2023, 3:26pm UTC](https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526/10 "2023-05-30T15:26:40Z")
I created a GLFWwindow window.
I suspect I need to “set” this window into vtkExternalOpenGLRenderWindow: correct? How to do that?
when I Render() on my vtkExternalOpenGLRenderWindow instance, I get:
```auto
X Error of failed request: BadWindow (invalid Window parameter)
Major opcode of failed request: 3 (X_GetWindowAttributes)
Resource id in failed request: 0x0
Serial number of failed request: 8
Current serial number in output stream: 9
```
When I comment the Render() call line, I get a black empty window (the GLFW one).
---
### Author:  [@fghoussen](https://discourse.vtk.org/u/fghoussen)
#### Post date: [May 31, 2023, 10:28am UTC](https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526/11 "2023-05-31T10:28:29Z")
Seems the GLUT example doesn’t link… Can’t figure out why…
```auto
[83%] Linking CXX executable ../../../../bin/vtkRenderingExternalCxxTests
/usr/bin/ld: CMakeFiles/vtkRenderingExternalCxxTests.dir/TestGLUTRenderWindow.cxx.o: in function `(anonymous namespace)::MakeCurrentCallback(vtkObject*, unsigned long, void*, void*)':
/home/fhoussen/Downloads/VTK/VTK-9.2.6/Rendering/External/Testing/Cxx/TestGLUTRenderWindow.cxx:75: undefined reference to `glutSetWindow'
/usr/bin/ld: CMakeFiles/vtkRenderingExternalCxxTests.dir/TestGLUTRenderWindow.cxx.o: in function `(anonymous namespace)::display()':
/home/fhoussen/Downloads/VTK/VTK-9.2.6/Rendering/External/Testing/Cxx/TestGLUTRenderWindow.cxx:144: undefined reference to `glutSwapBuffers'
/usr/bin/ld: CMakeFiles/vtkRenderingExternalCxxTests.dir/TestGLUTRenderWindow.cxx.o: in function `(anonymous namespace)::handleResize(int, int)':
/home/fhoussen/Downloads/VTK/VTK-9.2.6/Rendering/External/Testing/Cxx/TestGLUTRenderWindow.cxx:178: undefined reference to `glutPostRedisplay'
/usr/bin/ld: CMakeFiles/vtkRenderingExternalCxxTests.dir/TestGLUTRenderWindow.cxx.o: in function `TestGLUTRenderWindow(int, char**)':
/home/fhoussen/Downloads/VTK/VTK-9.2.6/Rendering/External/Testing/Cxx/TestGLUTRenderWindow.cxx:193: undefined reference to `glutInit'
```
---
### Author:  [@Jens\_Munk\_Hansen](https://discourse.vtk.org/u/Jens_Munk_Hansen)
#### Post date: [May 31, 2023, 6:08pm UTC](https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526/12 "2023-05-31T18:08:49Z")
Did you supply a valid installation path for glut when building VTK? The example still works for me.
---
### Author:  [@fghoussen](https://discourse.vtk.org/u/fghoussen)
#### Post date: [May 31, 2023, 7:46pm UTC](https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526/13 "2023-05-31T19:46:05Z")
No?!.. Isn’t CMake supposed to find GLUT (and friends) paths when expected options are ON?
What are the options you pass to cmake?
---
### Author:  [@Jens\_Munk\_Hansen](https://discourse.vtk.org/u/Jens_Munk_Hansen)
#### Post date: [May 31, 2023, 8:07pm UTC](https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526/14 "2023-05-31T20:07:36Z")
I would guess so. I usually use ccmake and search for options relevant. Sometimes I experience that it finds e.g a wrong python. It could be that the location for glut is wrong. But yes, if everything is done right things should work.
---
### Author:  [@sankhesh](https://discourse.vtk.org/u/sankhesh)
#### Post date: [June 8, 2023, 2:24am UTC](https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526/15 "2023-06-08T02:24:42Z")
@fghoussen Chances are the crash is because `glGenFrameBuffers` is being called without setting
up a valid OpenGL context. When using `vtkExternalOpenGLRenderWindow`, it is assumed that the application provided OpenGL context is valid. To ensure that this is the case, only call `Render` in the draw callback of your GLFW app.
---
### Author:  [@fghoussen](https://discourse.vtk.org/u/fghoussen)
#### Post date: [June 8, 2023, 4:18pm UTC](https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526/16 "2023-06-08T16:18:09Z")
I payed attention to initialize the context before anything else! Replacing `vtkExternalOpenGLRenderWindow` with `vtkRenderWindow` doesn’t trigger the crash but I get black screen with nothing rendered in it
---
### Author:  [@sankhesh](https://discourse.vtk.org/u/sankhesh)
#### Post date: [June 13, 2023, 12:56pm UTC](https://discourse.vtk.org/t/how-to-integrate-vtk-with-opengl/11526/17 "2023-06-13T12:56:58Z")
@fghoussen You should be using the `vtkExternalOpenGLRenderWindow` for sure. That is the render window sub-class that makes sure that VTK doesn’t create its own OpenGL context but hitches a ride in an externally created one. If you can, share your code that crashes - that would help get a better understanding of what’s going wrong.