#  PictureShowQt.py  (c) Kari Laitinen

#  http://www.naturalprogramming.com/

#  2009-11-16  File created.
#  2009-11-30  Last modification.

#  This program shows a sequence of pictures, changing the
#  picture after each 3 seconds.

#  A thread is used to time the picture change.

#  The picture files must be in the same folder where this
#  file is located.

import sys

from PyQt4.QtCore import *
from PyQt4.QtGui import *

from time import sleep 


class AnimationThread ( QThread ) :

   def __init__( self ) :

      QThread.__init__( self ) 

      self.thread_must_be_run  =  True

      self.mutex = QMutex() # I do not know if this really is useful.

      # print " thread init done "

   def stop_this_thread( self ) :

      self.thread_must_be_run = False


   def run( self ) :

      while  self.thread_must_be_run == True  :

         self.mutex.lock() # locking may not be necessary

         #  Here we emit a signal whenever we want a new picture
         #  to be drawn. The other thread will handle this signal
         #  so that the method change_picture_and_redraw() will
         #  be called.

         self.emit( SIGNAL( "picture_change_request" ) )

         self.mutex.unlock()
 
         sleep( 3.000 )  # Delay of three seconds.
         #QThread.sleep( 3 )  # An alternative way to sleep.

      # print " run method ends "


 
class PictureShowWindow( QWidget ) :

   def __init__( self, parent=None ) :

      QWidget.__init__( self, parent )

      self.setGeometry( 100, 100, 800, 600 )
 
      self.setWindowTitle( "SHOWING A SEQUENCE OF PICTURES" )

      picture_file_names  =  ( "yellow_field_by_vincent_van_gogh.jpg",
                               "night_watch_by_rembrandt.jpg",
                               "persistence_of_memory_by_dali.jpg",
                               "demoiselles_de_avignon_by_picasso.jpg",
                               "mona_lisa_by_leonardo.jpg" )

      self.pictures_to_be_shown  =  []

      for  file_name  in  picture_file_names :

         picture_to_be_shown  =  QImage( file_name )

         self.pictures_to_be_shown.append( picture_to_be_shown )
                      
      self.index_of_current_picture  =  0

      self.animation_thread  =  AnimationThread()

      self.connect( self.animation_thread,
                    SIGNAL( "picture_change_request" ),
                    self.change_picture_and_redraw )


      self.animation_thread.start()

   def change_picture_and_redraw( self ) :

      self.index_of_current_picture  +=  1

      if  self.index_of_current_picture  >=  len( self.pictures_to_be_shown ) :

         self.index_of_current_picture  =  0

      self.update()

   def paintEvent( self, event ) :

      painter = QPainter()
      
      painter.begin( self )
      
      painter.drawImage( 30, 20,
                  self.pictures_to_be_shown[ self.index_of_current_picture ] )

      painter.end()


   def exit_this_window( self ) :

      self.animation_thread.stop_this_thread()

      self.close() #is this necessary???


#  Here is the main program:

def main( args ) :

   this_application = QApplication( args )
   application_window = PictureShowWindow()
   application_window.show()

   # The following statement specifies that when the
   # "lastWindowClosed()" signal is emitted by QApplication,
   # the Python method exit_this_window is called for the
   # PictureShowWindow object.

   this_application.connect( this_application,
                             SIGNAL( "lastWindowClosed()" ),
                             application_window.exit_this_window )

   this_application.exec_()
  
if __name__== "__main__" :

   main( sys.argv )

#  Notes:

#  There are two methods for redrawing the screen area.
#  These are repaint() and update(). Qt Documentation says the
#  following about the use of these methods.

#  We suggest only using repaint() if you need an immediate repaint,
#  for example during animation. In almost all circumstances update()
#  is better, as it permits Qt to optimize for speed and minimize flicker.
#http://www.riverbankcomputing.co.uk/static/Docs/PyQt4/html/qwidget.html#repaint