Just thought I'd clear up some of the OpenGL/Togl/Tk issues in your post. Togl's overlay buffers need to be supported by the graphics card. Most PC graphics cards do not support overlay planes. You need a "workstation" card, such as a NVidia Quadro, a 3dLabs Wildcat, or an ATI FireGL card. glReadPixels is slow because graphics cards vendors say there is no incentive to make it fast. Talk to your vendor. OpenGL rubberbanding is best done with glLogicOp(GL_XOR). Tcl/Tk is slow compared to WxWindows. If you want GUI speed, go back to WxPython. OpenGL is same speed whether you are using WxWindows' wxGLCanvas or Tk's Togl. Hope this helps, Greg Couch UCSF Computer Graphics Lab