A call to
      glGetFramebufferAttachmentParameteriv(GL_DRAW_FRAMEBUFFER,
        attachment,
        GL_FRAMEBUFFER_ATTACHMENT_RED_SIZE, &size);
at vtkOpenGLRenderWindow.cxx:520 fails on my machine.

This is the valgrind printout before the fix
==818== Conditional jump or move depends on uninitialised value(s)
==818==    at 0x1A3B97CC: vtkRenderWindow::SetAlphaBitPlanes(int) (in /home/danlipsa/build/VTK-OpenGL2/lib/libvtkRenderingOpenGL2-6.3.so.1)
==818==    by 0x1A466BC7: vtkOpenGLRenderWindow::OpenGLInitState() (vtkOpenGLRenderWindow.cxx:396)
==818==    by 0x1A466AD7: vtkOpenGLRenderWindow::OpenGLInit() (vtkOpenGLRenderWindow.cxx:343)
==818==    by 0x1A4F275C: vtkXOpenGLRenderWindow::WindowInitialize() (vtkXOpenGLRenderWindow.cxx:976)
==818==    by 0x1A4F27A2: vtkXOpenGLRenderWindow::Initialize() (vtkXOpenGLRenderWindow.cxx:985)
==818==    by 0x1A4F2BE8: vtkXOpenGLRenderWindow::Start() (vtkXOpenGLRenderWindow.cxx:1112)
==818==    by 0x1A4E3F25: vtkXRenderWindowInteractor::Initialize() (vtkXRenderWindowInteractor.cxx:386)
==818==    by 0x12057613: vtkRenderWindow::Render() (vtkRenderWindow.cxx:320)
==818==    by 0x1A467095: vtkOpenGLRenderWindow::Render() (vtkOpenGLRenderWindow.cxx:448)
==818==    by 0x1A4F53AC: vtkXOpenGLRenderWindow::Render() (vtkXOpenGLRenderWindow.cxx:1765)
==818==    by 0x1A0F43BF: vtkXOpenGLRenderWindowCppCommand(vtkXOpenGLRenderWindow*, Tcl_Interp*, int, char**) (vtkXOpenGLRenderWindowTcl.cxx:434)
==818==    by 0x1A0F2D93: vtkXOpenGLRenderWindowCommand(void*, Tcl_Interp*, int, char**) (vtkXOpenGLRenderWindowTcl.cxx:32)
==818==