The window.pick function only works for that window. You will have to call the pick function for the specific window you are interested in. You can use the
viz.window.select command to get the current sub-window located at the specified screen position. I just noticed that this command is currently undocumented, so here is some example code showing how to use it:
Code:
# Get the sub-window located at the current mouse position
window = viz.window.select()
# Get the window located at the center of the screen
window = viz.window.select([0.5,0.5])
# Get the window located at pixel location (100,100)
window = viz.window.select([100,100],mode=viz.WINDOW_PIXELS)