Fade-in pixbuf box

fade_box_window.py

#!/usr/bin/python

from gi.repository import Gtk, GLib, Gdk
import cairo

class FadeBoxWindow(Gtk.Window):
    def __init__(self):
        super(FadeBoxWindow, self).__init__()

        self.init_ui()

    def init_ui(self):
        self.darea = Gtk.DrawingArea()
        self.darea.connect("draw", self.on_draw)
        self.darea.connect_after("draw", self.on_draw_after)
        self.add(self.darea)

        self.timer = True
        self.alpha = 0.0

        GLib.timeout_add(20, self.on_timer)

        self.set_title("Fade example")
        self.resize(350, 200)
        self.set_position(Gtk.WindowPosition.CENTER)
        self.connect("delete-event", Gtk.main_quit)
        self.show_all()

    def get_columns(self):
        c1 = Gdk.Rectangle()
        c1.x = c1.y = 30
        c1.width = c1.height = 20
        c2 = c1.copy()
        c2.x = 120
        c3 = c2.copy()
        c3.x = 200

        return (c1, c2, c3)

    def on_timer(self):
        
        if not self.timer: return False
    
        self.darea.queue_draw()
        return True

    def on_draw(self, widget, cr):
        columns = self.get_columns()

        w, h = self.get_size()
        cr.set_source_rgb(0.5, 0, 0)
        cr.rectangle(0, 0, w, h)
        cr.fill()

        for rect in columns:
            cr.set_source_rgb(0, 0.5, 0)
            cr.rectangle(rect.x, rect.y, rect.width, rect.height)
            cr.fill()

    def on_draw_after(self, widget, cr):
        columns = self.get_columns()
        self.alpha += 0.08

        for rect in columns:
            cr.save()

            pb = Gdk.pixbuf_get_from_surface(cr.get_target(), rect.x, rect.y, rect.width, rect.height)
        
            cr.rectangle(rect.x, rect.y, rect.width, rect.height)

            cr.set_source_rgb(0.5,0,0)
            cr.fill()
            Gdk.cairo_set_source_pixbuf(cr, pb, rect.x, rect.y)
            cr.paint_with_alpha(self.alpha)
            cr.restore()

        print(self.alpha)

        if self.alpha >= 1:
            self.timer = False

app = FadeBoxWindow()
Gtk.main()