[vtkusers] Using vtkExternalOpenGLCamera

[Ken Martin]

At least pieces of that code look out of date as the matrix and lighting
ops definitely will no longer work with the new OpenGL2 3.2 based backend.

But I have heard of people doing something like what you described, but
maybe they are using the vtkGenericOpenGLRenderWindow instead.

On Thu, Mar 22, 2018 at 1:45 PM, Gavin <gavin.wheeler at kcl.ac.uk> wrote:

> I've been using vtkExternalXXXX to try and integrate VTK into Unity, so
> this
> is a very interesting thread. However, the documentation and examples are a
> bit thin, and so I found myself rather confused...
>
> - I never realised a 'normal' camera and renderer can be used with the
> external render window - the documentation really does not point to this
> being a possibility. (Ditto the converse that an External Light needs to be
> used - I wondered why the lighting I added had no effect)
>
> I ended up deriving my own renderer class from vtkExternalOpenGLRenderer to
> stop it overwriting the View and Projection matrices I'd set. I'll try
> using
> the vtkOpenGLRenderer instead. I hope I can use the vtkExternalOpenGLCamera
> with this class - this is the one which adds the methods to set the View
> and
> Projection matrices. As I say I found it really unclear that if you use the
> vtkExternalOpenGLCamera to set the View and Projection Matrices they'll be
> overwritten if you also use vtkExternalOpenGLRenderer.
>
> - I never had any success getting vtkExternalOpenGLRenderer to acquire
> correct view and projection matrices
>
> I'm no OpenGL expert, so bear with me if I have totally the wrong idea
> here.
> When I look at the latest documentation for OpenGL (V4.6) the calls...
>
>   glGetDoublev(GL_MODELVIEW_MATRIX,mv);
>   glGetDoublev(GL_PROJECTION_MATRIX,p);
>
> ...as used in vtkExternalOpenGLRenderer::Render(void) don't appear to be
> supported. glGetDoublev is a function but GL_MODELVIEW_MATRIX and
> GL_PROJECTION_MATRIX are not defined - see
> https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glGet.xhtml
>
> However, they do seem to be defined for OpenGL 2.1
> https://www.khronos.org/registry/OpenGL-Refpages/gl2.1/xhtml/glGet.xml
>
> Which to me makes sense as I understand the pipeline is user defined for
> OpenGL 3+ but was defined OpenGL 2.X
>
> So, am I wrong in thinking that vtkExternalOpenGLRenderer will only work
> with older versions of OpenGL? That's how it appears to me, I've found
> nothing to say what versions are(n't) supported. If I am wrong, please
> correct me and explain why - I'm keen to learn more about how this all
> works
> and to help in my future development.
>
> Thanks, G
>
>
>
>
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-- 
Ken Martin PhD
Distinguished Engineer
Kitware Inc.
28 Corporate Drive
Clifton Park NY 12065

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