main.py

#!/usr/bin/kivy
import kivy
#kivy.require('1.0.6')

from kivy.app import App
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.label import Label
from kivy.graphics import Color, Rectangle, Point, GraphicException
from kivy.clock import Clock
from kivy.logger import Logger
from random import random
from math import sqrt
import socket
import struct
import time
import threading
import Queue


import socket
def get_ip():
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    try:
        s.connect(('google.com', 0))
        return s.getsockname()[0]
    finally:
        s.close()

def get_broadcast_addr(ip):
    # XXX
    return ip.rsplit('.', 1)[0] + '.255'

ip = get_ip()
broadcast_ip = get_broadcast_addr(ip)
addr = broadcast_ip, 9876
# Because of rp_filter, can't use <broadcast> or 255.255.255.255

coord_struct = struct.Struct('>Q2d')
q = Queue.Queue()

def remake_socket():
    global s, addr
    addr = broadcast_ip, 9876
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    s.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, 1)
    s.bind(('', 9876))
remake_socket()


def calculate_points(x1, y1, x2, y2, steps=5):
    dx = x2 - x1
    dy = y2 - y1
    dist = sqrt(dx * dx + dy * dy)
    if dist < steps:
        return None
    o = []
    m = dist / steps
    for i in range(1, int(m)):
        mi = i / m
        lastx = x1 + dx * mi
        lasty = y1 + dy * mi
        o.extend([lastx, lasty])
    return o

def recv_loop():
    while True:
        try:
            recv_loop_real()
        except socket.error as e:
            print e
            remake_socket()

def recv_loop_real():
    global addr
    s.sendto('START', addr)
    try:
        while True:
            data, a = s.recvfrom(65536)
            if a[0] == ip:
                #ignore packet came from same host.
                continue
            elif data.startswith('START'):
                Logger.info('Received {} from {}'.format(data, a))
                Logger.info('Received {} from {}'.format(data, a))
                Logger.info('Received {} from {}'.format(data, a))
                Logger.info('Received {} from {}'.format(data, a))
                Logger.info('Received {} from {}'.format(data, a))
                addr = a
                if data == 'START':
                    s.sendto('STARTED', a)
            else:
                for i in range(len(data)/coord_struct.size):
                    pos = coord_struct.unpack(data[i*coord_struct.size:(i+1)*coord_struct.size])
                    q.put(pos)
    finally:
        s.close()

def my_callback(dt):
    while q.unfinished_tasks:
        uid, x, y = q.get()
        app.tracer.add_line(uid + 0x00100000, x, y)
        q.task_done()

class Touchtracer(FloatLayout):
    def __init__(self, *args, **kwargs):
        super(Touchtracer, self).__init__(*args, **kwargs)
        self.lines = {}
        self.buf = []
    def add_line(self, uid, x, y):
        #g = str(uid)
        #self.c = Color(1, 1, 1, mode='hsv', group=g)
        with self.canvas:
            if uid not in self.lines:
                self.lines[uid] = Point(points=(x,y), source='particle.png', pointsize=5)#, group=g)
            else:
                self.lines[uid].add_point(x, y)

    def on_touch_down(self, touch):
        win = self.get_parent_window()
        ud = touch.ud
        ud['group'] = g = str(touch.uid)
        with self.canvas:
            ud['color'] = Color(random(), 1, 1, mode='hsv', group=g)
            ud['lines'] = (
                Rectangle(pos=(touch.x, 0), size=(1, win.height), group=g),
                Rectangle(pos=(0, touch.y), size=(win.width, 1), group=g),
                Point(points=(touch.x, touch.y), source='particle.png',
                      pointsize=5))#, group=g))
            self.send_point(touch.uid, touch.x, touch.y)
        #ud['label'] = Label(size_hint=(None, None))
        #self.update_touch_label(ud['label'], touch)
        #self.add_widget(ud['label'])
        touch.grab(self)
        return True

    def send_point(self, uid, x, y):
        dgram = coord_struct.pack(uid, x, y)#touch.uid, points[idx], points[idx+1])
        self.buf.append(dgram)
        if len(self.buf) >= 100:
            self.flush()

    def flush(self):
        if not self.buf:
            return
        buf, self.buf = self.buf, []
        dgram = b''.join(buf)
        try:
            s.sendto(dgram, addr)
        except socket.error:
            pass

    def on_touch_move(self, touch):
        if touch.grab_current is not self:
            return
        ud = touch.ud
        ud['lines'][0].pos = touch.x, 0
        ud['lines'][1].pos = 0, touch.y

        points = ud['lines'][2].points
        oldx, oldy = points[-2], points[-1]
        points = calculate_points(oldx, oldy, touch.x, touch.y)
        if points:
            try:
                lp = ud['lines'][2].add_point
                for idx in range(0, len(points), 2):
                    self.send_point(touch.uid, points[idx], points[idx+1])
                    lp(points[idx], points[idx+1])
            except GraphicException:
                pass

    def on_touch_up(self, touch):
        if touch.grab_current is not self:
            return
        touch.ungrab(self)
        ud = touch.ud
        self.canvas.remove_group(ud['group'])
        if touch.x < 100 and touch.y < 100:
            self.canvas.clear()
        else:
            self.flush()


class TouchtracerApp(App):
    title = 'Touchtracer'
    icon = 'icon.png'

    def build(self):
        self.tracer = Touchtracer()
        return self.tracer

    def on_pause(self):
        return True

if __name__ == '__main__':
    app = TouchtracerApp()
    t = threading.Thread(target=recv_loop)
    t.daemon = True
    t.start()
    Clock.schedule_interval(my_callback, 0.01)
    app.run()

touchtracer.kv

#:kivy 1.0
#:import kivy kivy

<Touchtracer>:
    canvas:
        Color:
            rgb: 1, 1, 1
        #Rectangle:
        #    source: 'data/images/background.jpg'
        #    size: self.size

    BoxLayout:
        padding: '10dp'
        spacing: '10dp'
        size_hint: 1, None
        pos_hint: {'top': 1}
        height: '44dp'
        #Image:
        #    size_hint: None, None
        #    size: '24dp', '24dp'
        #    source: 'data/logo/kivy-icon-64.png'
	#		mipmap: True
        #Label:
        #    height: '24dp'
        #    text_size: self.width, None
        #    color: (1, 1, 1, .8)
        #    text: 'Kivy %s - Touchtracer' % kivy.__version__
        #    valign: 'middle'