Hi Roberto

small example

hope this helps :)

from AppKit import NSTimer
from random import random

from vanilla import *

from mojo.canvas import Canvas
import mojo.drawingTools as dt

from lib.baseObjects import CallbackWrapper

class Test(object):
    
    def __init__(self):
        self.pos = 0, 0
        self.width = 400
        self.height = 400
        self.size = 100
        self.steps = 5
        self.addHorizontal = True
        self.directionX = 1
        self.directionY = 1
        
        framePerSecond = 30
        
        self.interval = framePerSecond / 1000.
        
        self.w = Window((400, 400))
        
        self.w.canvas = Canvas((0, 0, 400, 400), self, canvasSize=(self.width, self.height))
        self.w.open()
        
        self._callback = CallbackWrapper(self.redraw)
        self.sheduleTimer()
    
    def sheduleTimer(self):
        if self.w.getNSWindow() is not None:
            self.trigger = NSTimer.scheduledTimerWithTimeInterval_target_selector_userInfo_repeats_(self.interval, self._callback, "action:", None, False)
    
    def redraw(self, timer):
        self.w.canvas.update()
        self.sheduleTimer()
    
    def draw(self):
        x, y = self.pos
        if self.addHorizontal:
            x += self.steps  * self.directionX
        else:
            y += self.steps  * self.directionY
        
        if x > (self.width - self.size):
            self.addHorizontal = False
            x = self.width - self.size
            self.directionX *= -1
        elif x < 0:
            self.addHorizontal = False
            x = 0     
            self.directionX *= -1       
        
        if y > (self.height - self.size):
            self.addHorizontal = True
            y = self.height - self.size
            self.directionY *= -1
        elif y < 0:
            self.addHorizontal = True
            y = 0
            self.directionY *= -1
        
        dt.fill(x/float(self.width), y/float(self.height), 1)
        dt.rect(x, y, self.size, self.size)
        
        self.pos = x, y

Test()