Rendering VTK in external OpenGL context with single buffering

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1

Hi All!

I want to render a circle (to start off slow) using VTK in an existing application. We use GLFW to create a window and the OpenGL context as well as GLAD for the bindings. I presume that vtkExternalOpenGLRenderWindow would be the tool to use in this case.

After some successful experiments I found a problem I cannot solve: Our application uses single buffering (hard requirement) and additionally we want to render VTK into a FBO, for a later use/composition. The problem I ran into is that the circle is rendered but VTK attempts to bind GL_BACK_LEFT to the DrawBuffer and ReadBuffer, which does not exist in our context and the debug callback reports it as an error. I am concerned about stability implications of our application under these circumstances, and I wonder if there is a better way to embed VTK into a pre-existing single-buffer OpenGL context.

Any help is much appreciated!

2

You should be able to disable double buffering using vtkWindow::SetDoubleBuffer. By default, this is enabled by vtkRenderWindow.

3

Thanks @sankhesh for your tip! Unfortunately, I already use this flag with no affect. When looking into the source code I can see, that the DoubleBuffer flag is not used to check if the buffers are there in the initialization of the vtkOpenGLState object.

Could it be that this is a bug?

4

Is it possible that calling SetDoubleBuffer() earlier would work : e.g. just after in your vtkRenderWindow instance construction ?

Here’s the code I got from a quick look to 9.2.2 sources and I can read:

vtkRenderWindow::vtkRenderWindow()
{
  this->DoubleBuffer = 1;
}

So I would try to set it (using the wrapping set function SetDoubleBuffer() ) just after my smartPointer allocation of the vtkRenderWindow object that should call this constructor ?

5

I believe the original issue of looking at DoubleBuffer when initializing vtkOpenGLState has already been fixed. @Carol_Capek could you confirm?

@fab672000 Are you running into a similar issue?

6

I actually never got it to run. I went for a rather hacky solution where I use an offscreen context, without error propagation, besides my main context.

I tried to look into the code again today, but i couldn’t wrap my head around it again in a meaningful time. I will check my version again and upgrade if possible. Will keep you posted.

7

No as using double buffering does not cause me issues and allows for faster fps at this time, but using opengl acceleration too, I was just interested by this issue.

Thanks for providing feedback on this.

8

Following up: I tried the new version 9.2.2 and apparently the bug is gone. Thanks for letting me know @sankhesh !

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