[vtkusers] Problems performing off-screen rendering with vtk-5.3.x, Qt-4.5.x and Cocoa 64-bit libraries

[clinton at elemtech.com]

>
> Offscreen mode first creates a window to be able to create an OpenGL
> context on which OpenGL version and extensions can be queried to find
> out if the framebuffer object extension (FBO) is
> supported (as well as none-power-of-two textures (NPOT) and
> rectangular textures). If so, it will create an FBO and render in it
> instead of the window. If not, it destroys the window. In your case,
> it probably does not find this extension. Note: this is the only
> offscreen mode supported by VTK on Carbon and Cocoa.
> With FBO, the rendering happens offscreen but it does not prevent to
> have at least a dummy window to show up.

The vtkCarbonRenderWindow does have a fallback offscreen method using AGL if 
FBO isn't supported.  Which is why the user didn't have problems with Carbon, 
but did with Cocoa.

Is it required to go as far as showing the window on the screen, or is it 
enough just to make an invisible window?

Clint