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