The first thing an application using OcempGUI should do is to
initialize the renderering system. The
Renderer class from the
ocempgui.widgets package contains all
necessary parts to take care of this. It includes
the event mangement
a sprite based render engine
methods to create the pygame window
The Renderer can be set up with only
three lines of code.
Now that the Renderer is set up, you
can start to place widgets on the pygame window by adding them
using the Renderer.add_widget()
method. Let us do this by building a simple (and well-known)
application with a Button widget on it,
that displays 'Hello World'.
You can find the example as python script under
examples/hello_world.py
# Hello World example.
from ocempgui.widgets import *
# Initialize the drawing window.
re = Renderer ()
re.create_screen (100, 50)
re.title = "Hello World"
re.color = (250, 250, 250)
button = Button ("Hello World")
button.position = (10, 10)
re.add_widget (button)
# Start the main rendering loop.
re.start ()
Example 21. Hello World with OcempGUI
The second line
from ocempgui.widgets import*
ocempgui.widgets module you will need
to build an application. It is also possible to use a fine
grained selection of classes and submodules to import, but
mostly the above code will serve well.
The fifth and sixth lines
re = Renderer ()
re.create_screen (100, 50)
Renderer object, which
takes care of updating the screen and the event management and
create a pygame window with a 100x50 size.
The seventh and eight line
re.title = "Hello World"
re.color = (250, 250, 250)
In line ten
button = Button ("Hello World")Button widget is created. The
constructor can receive an additional argument with the text,
the Button should display.
The next line will place the Button at
a specific position.
button.position = (10, 10)
Line twelve
re.add_widget (button)
The last line will start the main processing loop of the
Renderer.
re.start ()
Renderer, which will wait
for events, draw and update the widgets and so on.
Every widget of OcempGUI inherits from the
ocempgui.object.BaseObject class and
its event handling makes heavy usage of the
BaseObject features.
To cause a Button to print a message
upon a mouse click, you would connect a message printing
function to the click signal of the
Button. In turn, if this callback is
not needed anymore in the later program flow, you would
disconnect the function from the
Button's signal.
This theoretical model is used in many different toolkits and
OcempGUI stays with it. We will enhance our 'Hello world'
example application from the previous chapter with a callback
now, wich prints a message each time the
Button is clicked.
You can find the example as python script under
examples/hello_world_signals.py
# Hello World example.
from ocempgui.widgets import *
from ocempgui.widgets.Constants import *
def print_message ():
print "The button was clicked!"
# Initialize the drawing window.
re = Renderer ()
re.create_screen (100, 50)
re.title = "Hello World"
re.color = (250, 250, 250)
button = Button ("Hello World")
button.position = (10, 10)
button.connect_signal (SIG_CLICKED, print_message)
re.add_widget (button)
# Start the main rendering loop.
re.start ()
Example 22. Hello World with callbacks
The first change you note is the new import directive in line three.
from ocempgui.widgets.Constants import *
ocempgui.widgets module. The availabe
signal identifiers used by the various widgets of OcempGUI
area prefixed with SIG_.
Line five and six contain the function, which will be used as the callback for the button. It is indifferent, if the callback is a class or object method or a function. Both cases will work in the same way.
The next notably change was done in line 16
button.connect_signal (SIG_CLICKED, print_message)
Button to invoke the
print_message function each time it
is clicked. You also could send additional data to the
callback as you already know from the section called “Making objects event capable - the better way”. Anything written about
the signal handling of the BaseObject
class applies to the widgets, too.