PYGLET – On Expose Event

In this article, we will see how we can trigger an expose event in PYGLET module in python. Pyglet is easy to use but a powerful library for developing visually rich GUI applications like games, multimedia etc. A window is a “heavyweight” object occupying operating system resources. Windows may appear as floating regions or can be set to fill an entire screen (fullscreen). This event is triggered when the window first appears, and any time the contents of the window are invalidated due to another window obscuring it. There is no way to determine which portion of the window needs redrawing. Note that the use of this method is becoming increasingly uncommon, as newer window managers composite windows automatically and keep a backing store of the window contents.
We can create a window with the help of command given below 

pyglet.window.Window(width, height, title)

Below is the syntax of the on expose event, this method get called when this event is triggered 

@window.event       
def on_expose():
    print("On Expose Event")

Below is the implementation 

Python3

# importing pyglet module
import pyglet
import pyglet.window.key

# width of window
width = 500

# height of window
height = 500

# caption i.e title of the window
title = "Geeksforgeeks"

# creating a window
window = pyglet.window.Window(width, height, title)

# text
text = "GeeksforGeeks"

# creating a label with font = times roman
# font size = 36
# aligning it to the center
label = pyglet.text.Label(text,
                          font_name ='Times New Roman',
                          font_size = 36,
                          x = window.width//2, y = window.height//2,
                          anchor_x ='center', anchor_y ='center')


# on draw event
@window.event
def on_draw():

    # clearing the window
    window.clear()

    # drawing the label on the window
    label.draw()


# key press event
@window.event
def on_key_press(symbol, modifier):

    print("nn")
    # key "C" get press
    if symbol == pyglet.window.key.C:

        # close the window
        window.close()


# on expose event
@window.event
def on_expose():

    # printing some message
    print("On Expose event")




# image for icon
img = image = pyglet.resource.image("logo.png")

# setting image as icon
window.set_icon(img)

# start running the application
pyglet.app.run()

Output :