gistfile1.txt

#!/usr/bin/python

from __future__ import division
import math
import time

import cairo
import gi

gi.require_version('Gtk', '3.0')
from gi.repository import Gtk, Gdk
from gi.repository.GdkPixbuf import Pixbuf

def clear_surface(w, h, surface):

    cr = cairo.Context(surface)
    cr.set_source_rgb(0,  0, 0)

    cr.paint()
    del cr



def draw_brush(widget, x, y, odata, width=12.5, r=220/255, g=240/255, b=90/255, alpha=0.5):

    cr = cairo.Context(widget.surface)
    
    cr.set_source_rgba(r, g, b, alpha)
    cr.set_line_width(width)
    cr.set_line_cap(1)
    cr.set_line_join(cairo.LINE_JOIN_ROUND)   
    cr.new_path()

    head = odata[-2]
    point = odata[-1]

    cr.move_to(head['x'], head['y']+2.5)
    cr.line_to(point['x'], point['y']+1.5)

    cr.stroke()


class Example(Gtk.Window):

    def __init__(self):
        super(Example, self).__init__()
        
        self.set_border_width(8)
        self.odata = []
        self.box = Gtk.Box(spacing=6)
        self.add(self.box)
        da = Gtk.DrawingArea()
        self.box.pack_start(da, True, True, 0)

        window = Gdk.get_default_root_window()

        self.set_default_size(400, 400)
        da.surface = None
        da.connect('draw', self.draw)
        da.connect('configure-event', self.configure_event_cb)

        da.connect('motion-notify-event', self.motion_notify_event_cb)
        da.connect('button-press-event', self.button_press_event_cb)
        da.connect('button-release-event', self.button_release)
        da.set_events(da.get_events() |
                      Gdk.EventMask.BUTTON_PRESS_MASK |
                      Gdk.EventMask.POINTER_MOTION_MASK |
                      Gdk.EventMask.BUTTON_RELEASE_MASK)

        self.da = da
        self.connect('destroy', self.close_window)
        self.show_all()

    def button_release(self, widget, event):
        self.odata = []

    def draw(self, widget, cr):

        cr.set_source_surface(self.da.surface, 0, 0)
        cr.paint()
        return False

    def configure_event_cb(self, widget, event):
        """
        Called the windows is first created. Here we also load the
        background image, via the call to clear
        """
        self.odata = []
        if self.da.surface is not None:
            del self.da.surface
            self.da.surface = None

        win = widget.get_window()
        w = widget.get_allocated_width()
        h = widget.get_allocated_height()
        
        widget.surface = win.create_similar_surface(
            cairo.CONTENT_COLOR,
            w, h)
                        
        clear_surface(w, h, widget.surface)
        return True

    def button_press_event_cb(self, widget, event):
        """
        When the signal handler returns True, it means no further processing is done.
        E.g. there will be no propagation further. On the contrary, sending False,
        propagates the signal further.
        See documentation here:
        https://developer.gnome.org/gtk3/stable/GtkWidget.html#GtkWidget-button-press-event
        """

        if widget.surface is None:
            return False

        if event.button == Gdk.BUTTON_PRIMARY:
            if self.odata:
               self.odata = []
            point = {'x': event.x, 'y': event.y, 'd': False}
            self.odata.append(point)    
            pass
        elif event.button == Gdk.BUTTON_SECONDARY:
            win = widget.get_window()
            width = widget.get_allocated_width()
            height = widget.get_allocated_height()
            pixbuf = Gdk.pixbuf_get_from_window(win, 0, 0,
                                                width, height)
                            
            clear_surface(width*0.95, height*0.95, widget.surface)
            widget.queue_draw()

        return False

    def motion_notify_event_cb(self, widget, event):

  

        if widget.surface is None:
            return False

        if event.state & Gdk.EventMask.BUTTON_PRESS_MASK:
            point = {'x': event.x, 'y': event.y, 'd': False}
 

            self.odata.append(point)
            draw_brush(self.da, event.x, event.y, self.odata)

            widget.queue_draw()
            
        return True

    def close_window(self, window):

        if self.da is not None:
            del self.da.surface
            self.da.surface = None

        Gtk.main_quit()


def main():

    Example()
    Gtk.main()


if __name__ == "__main__":
    main()