如何使用 PyGTK 和 PyCairo 在窗口中获得透明背景？

我一直在努力使用 PyGTK 创建一个没有装饰和透明背景的窗口。然后我会用 Cairo 绘制窗口的内容。但我无法让它发挥作用。

我尝试了很多不同的方法，但都失败了，这是其中之一

#!/usr/bin/env python

import pygtk
pygtk.require('2.0')
import gtk, sys, cairo

win = None

def expose (widget, event):
    cr = widget.window.cairo_create()

    #Start drawing
    cr.set_operator(cairo.OPERATOR_CLEAR)
    cr.set_source_rgba(0.5,1.0,0.0,0.5)
    cr.rectangle(0, 0, 0.9, 0.8)
    cr.fill()

def main (argc):
    global win

    win = gtk.Window()

    win.set_decorated(False)

    win.connect('delete_event', gtk.main_quit)
    win.connect('expose-event', expose)

    win.set_app_paintable(True)

    win.show()

    gtk.main()

if __name__ == '__main__':
    sys.exit(main(sys.argv))

那么，最简​​单的方法是什么？

所以，我实际上自己弄清楚了这一点。

这是一个工作示例。我已经评论了相关部分，以防其他人对如何执行此操作感兴趣。

#!/usr/bin/env python

import pygtk
pygtk.require('2.0')
import gtk, sys, cairo
from math import pi

def expose (widget, event):
    cr = widget.window.cairo_create()

    # Sets the operator to clear which deletes everything below where an object is drawn
    cr.set_operator(cairo.OPERATOR_CLEAR)
    # Makes the mask fill the entire window
    cr.rectangle(0.0, 0.0, *widget.get_size())
    # Deletes everything in the window (since the compositing operator is clear and mask fills the entire window
    cr.fill()
    # Set the compositing operator back to the default
    cr.set_operator(cairo.OPERATOR_OVER)

    # Draw a fancy little circle for demonstration purpose
    cr.set_source_rgba(0.5,1.0,0.0,1)
    cr.arc(widget.get_size()[0]/2,widget.get_size()[1]/2,
           widget.get_size()[0]/2,0,pi*2)
    cr.fill()

def main (argc):

    win = gtk.Window()

    win.set_decorated(False)

    # Makes the window paintable, so we can draw directly on it
    win.set_app_paintable(True)
    win.set_size_request(100, 100)

    # This sets the windows colormap, so it supports transparency.
    # This will only work if the wm support alpha channel
    screen = win.get_screen()
    rgba = screen.get_rgba_colormap()
    win.set_colormap(rgba)

    win.connect('expose-event', expose)

    win.show()