[vtk-developers] vtk performance - issue 1 - OpenGL state

[Ken Martin]

> This first issue has to do with unnecessary calls to set
> OpenGL state (please excuse me if this terminology is incorrect,
> I'm not an OpenGL expert).
> It seems that the best thing to do would be to have something keep
> track of the state and only make the gl calls to change things
> that need to be changed. The place that would seem to make the
> most sense to do this would be within the renderer itself.
> The proposed solution is to add the ability of the renderer to
> keep track of this state and functions for the property
> (and anything
> else that changes these states) to call to set them. Then the
> renderer will only change them if they need to be changed.

The render window is the right place since it has a 1 to 1 mapping
with the OpenGL context. I would suggest in OpenGLProperty doing a
safe cast to an OpenGLRenderWindow and then calling all the opengl
methods on the OpenGLRenderWindow which will keep track of state in
its ivars and only make the OpenGL call if required. To make this fly
the OpenGLRenderWindow classes must be reorganized.  I would suggest

vtkRenderWindow  ---> vtkOpenGLRenderWindow -->

(vtkWin32OpenGLRenderWindow and vtkXOpenGLRenderWindow)

Where the platform independent code is in vtkOpenGLRenderWindow and
the Win32 and X code is in the respective subclasses. Also some of the
OpenGL calls in Property can probably be eliminated with a few if else
statements.

Ken