Sure, <window>.setSize() works during runtime as well, so for finding the right window size by tweaking it step-by-step you can have a little code like this:
Code:
x = 0.5 #initial size window X
y = 0.5 #initial size window Y
upLeftWindow = viz.addWindow()
upLeftWindow.setSize([x,y])
upLeftWindow.setPosition(0,1)
upLeftWindow.clearcolor(viz.WHITE)
def onKeyDown(key):
global x, y
if key == '-':
x -= 0.05 #step size
upLeftWindow.setSize([x,y])
elif key == '=':
x += 0.05 #step size
upLeftWindow.setSize([x,y])
print x, y
viz.go()
viz.callback(viz.KEYDOWN_EVENT,onKeyDown)
Pressing - or = will increase or decrease the X size of the window, you can map other keys for the Y size in a similar fashion.