#!/usr/bin/env python
#------------------------------------------------------------------------------ 
import sys
import gtk
import cairo
if gtk.pygtk_version < (2,9,0):
    print "PyGtk 2.9.0 or later required"
    raise SystemExit
#------------------------------------------------------------------------------ 
#------------------------------------------------------------------------------ 

class Dock(gtk.DrawingArea):
    def __init__(self):
        gtk.DrawingArea.__init__(self)
        # Override expose, called when we need to draw windows contents
        self.connect("expose_event", self.expose)
    
    def expose(self, widget, event):
        global alpha_support
        
        # Initialize our context
        self.context = widget.window.cairo_create()
        
        # Set a clip region for the expose event
        self.context.rectangle(event.area.x, event.area.y, 
                               event.area.width, event.area.height)
        self.context.clip()
        
        # Are we able to use alpha channels?
        if alpha_support:
            self.context.set_source_rgba(1.0, 1.0, 1.0, 0.0) # Transparent
        else:
            self.context.set_source_rgb(1.0, 1.0, 1.0) # Opaque white
            
        # Paint the background
        self.context.set_operator(cairo.OPERATOR_SOURCE)
        self.context.paint()

        # Now draw the rest...
        self.draw(self.context)
       
        return False
    
    def screen_changed(self, widget, old_screen=None):
        global alpha_support
        
        # To check if the display supports alpha channels, get the colormap
        screen = widget.get_screen()
        colormap = screen.get_rgba_colormap()
        
        if colormap == None:
            print 'WARNING: Alpha channel not supported!'
            colormap = screen.get_rgb_colormap()
            alpha_support = False
        else:
            alpha_support = True
            
        # Now we can set our colormap
        widget.set_colormap(colormap)
        
        return False

    def draw(self, context):
        # method to be overriden
        
        # get widget properties
        rect = self.get_allocation()
        
        # Draw a blue circle
        context.set_source_rgba(0.2, 0.2, 1.0, 0.6)
        radius = float((rect.width, rect.height)[rect.width>rect.height])/2 - 0.8
        context.arc(float(rect.width)/2, float(rect.height)/2, radius, 0, 2.0*3.14)
        context.fill_preserve()
        
        # Black line border
        context.set_source_rgba(0.0, 0.0, 0.0, 1.0)
        context.stroke()
    
def main(Widget):
    # Create our window and dock
    window = gtk.Window()
    window.connect("destroy", gtk.main_quit)
        
    # Tell GTK+ that we want to draw the windows background ourself.
    window.set_app_paintable(True)
    
    # Add the dock in there
    dock = Widget()
    window.set_default_size(300,400)
    window.add(dock)
    
    # Override default screen-changed Window function.
    window.connect("screen-changed", dock.screen_changed)
    dock.screen_changed(window)
    
    # Disable window frame    
    window.set_decorated(False)
    window.set_position(1)
       
    # and finally show the window.
    window.show_all()
    gtk.main()
    
if __name__ == "__main__":
    sys.exit(main(Dock))