April 2024 - This site, and Kamaelia are being updated. There is significant work needed, and PRs are welcome.


Pygame Display Access

This component provides a pygame window. Other components can request to be notified of events, or ask for a pygame surface or video overlay that will be rendered onto the display.

Pygame Display is a service that registers with the Coordinating Assistant Tracker (CAT).

Example Usage

See the Button component or VideoOverlay component for examples of how Pygame Display can be used.

How does it work?

Pygame Display is a service. obtain it by calling the PygameDisplay.getDisplayService(...) static method. Any existing instance will be returned, otherwise a new one is automatically created.

Alternatively, if you wish to configure Pygame Display with options other than the defaults, create your own instance, then register it as a service by calling the PygameDisplay.setDisplayService(...) static method. NOTE that it is only advisable to do this at the top level of your system, as other components may have already requested and created a Pygame Display component!

pygame only supports one display window at a time, you must not make more than one Pygame Display component.

Pygame Display listens for requests arriving at its "notify" inbox. A request can be to: - create or destroy a surface, - listen or stop listening to events (you must have already requested a surface) - move an existing surface - create a video overlay - notify of ne to redraw

The requests are described in more detail below.

Once your component has been given the requested surface, it is free to render onto it whenever it wishes. It should then immediately send a "REDRAW" request to notify Pygame Display that the window needs redrawing.

NOTE that you must set the alpha value of the surface before rendering and restore its previous value before yielding. This is because Pygame Display uses the alpha value to control the transparency with which it renders the surface.

Overlays work differently: instead of being given something to render to, you must provide, in your initial request, an outbox to which you will send raw yuv (video) data, whenever you want to change the image on the overlay.

Pygame Display instantiates a private, threaded component to listen for pygame events. These are then forwarded onto Pygame Display.

Pygame Display's main loop continuously renders the surfaces and video overlays onto the display, and dispatches any pygame events to listeners. The rendering order is as follows: - background fill (default=white) - surfaces (in the order they were requested and created) - video overlays (in the order they were requested and created)

In summary, to use a surface, your component should: 1. Obtain and wire up to the "notify" inbox of the Pygame Display service 2. Request a surface 3. Render onto that surface in its main loop

And to use overlays, your component should: 1. Obtain and wire up to the "notify" inbox of the Pygame Display service 2. Request an overlay, providing an outbox 3. Send yuv data to the outbox

This component does not terminate. It ignores any messages arriving at its "control" inbox and does not send anything out of its "outbox" or "signal" outboxes.


To request a surface, send a dictionary to the "notify" inbox. The following keys are mandatory:

    "DISPLAYREQUEST" : True,               # this is a 'new surface' request
    "size" : (width,height),               # pixels size for the new surface
    "callback" : (component, "inboxname")  # to send the new surface object to

These keys are optional:

    "position" : (left,top)                # location of the new surface in the window (default=arbitrary)
    "alpha" : 0 to 255,                    # alpha of the surface (255=opaque) (default=255)
    "transparency" : (r,g,b),              # colour that will appear transparent (default=None)
    "events" : (component, "inboxname"),   # to send event notification to (default=None)

To deregister your surface, send a producerFinished(surface) message to the "notify" inbox. Where 'surface' is your surface. This will remove your surface and deregister any events you were listening to.

To change the position your surface is rendered at, send a dictionary to the "notify" inbox containing the folling keys:

    "CHANGEDISPLAYGEO" : True,             # this is a 'change geometry' request
    "surface" : surface,                   # the surface to affect
    "position" : (left,top)                # new location for the surface in the window

The "surface" and "position" keys are optional. However if either are not specified then there will be no effect!

Listening to events

Once your component has obtained a surface, it can request to be notified of specific pygame events.

To request to listen to a given event, send a dictionary to the "notify" inbox, containing the following:

    "ADDLISTENEVENT" : pygame_eventtype,     # example: pygame.KEYDOWN
    "surface" : your_surface,

To unsubscribe from a given event, send a dictionary containing:

    "REMOVELISTENEVENT" : pygame_eventtype,
    "surface" : your_surface,

Events will be sent to the inbox specified in the "events" key of the "DISPLAYREQUEST" message. They arrive as a list of pygame event objects.

NOTE: If the event is MOUSEMOTION, MOUSEBUTTONUP or MOUSEBUTTONDOWN then you will instead receive a replacement object, with the same attributes as the pygame event, but with the 'pos' attribute adjusted so that (0,0) is the top left corner of your surface.

Video Overlays

To request an overlay, send a dictionary to the "notify" inbox. The following keys are mandatory:

    "OVERLAYREQUEST" : True,                      # this is a 'new overlay' request
    "size" : (width,height),                      # pixels size of the overlay
    "pixformat" : pygame_pixformat,               # example: pygame.IYUV_OVERLAY

These keys are optional:

    "position" : (left,top),                      # location of the overlay (default=(0,0))
    "yuv" : (ydata,udata,vdata),                  # first frame of yuv data
    "yuvservice" : (component,"outboxname"),      # source of future frames of yuv data
    "positionservice" : (component,"outboxname"), # source of changes to the overlay position

"yuv" enables you to provide the first frame of video data. It should be 3 strings, containing the yuv data for a whole frame.

If you have supplied a (component,outbox) pair as a "yuvservice" then any (y,u,v) data sent to that outbox will update the video overlay. Again the data should be 3 strings, containing the yuv data for a whole frame.

If you have supplied a "positionservice", then sending (x,y) pairs to the outbox you specified will update the position of the overlay.

There is currently no mechanism to destroy an overlay.

Redraw requests

To notify Pygame Display that it needs to redraw the display, send a dictionary containing the following keys to the "notify" inbox:

    "REDRAW" : True,             # this is a redraw request
    "surface" : surface          # surface that has been changed

Implementation Details

You may notice that this module also contains a _PygameEventSource component. PygameDisplay uses this separate threaded component to notify it when pygame events occur - so that it can sleep quiescently when it has nothing to do.

Unfortunately event handling itself cannot be done in the thread since pygame on many platforms (particularly win32) does not work properly if event handling and display creation is not done in the main thread of the program.


class PygameDisplay(Axon.AdaptiveCommsComponent.AdaptiveCommsComponent)

PygameDisplay(...) -> new PygameDisplay component

Use PygameDisplay.getDisplayService(...) in preference as it returns an existing instance, or automatically creates a new one.

Or create your own and register it with setDisplayService(...)

Keyword arguments (all optional):

  • width -- pixels width (default=800)
  • height -- pixels height (default=600)
  • background_colour -- (r,g,b) background colour (default=(255,255,255))
  • fullscreen -- set to True to start up fullscreen, not windowed (default=False)


  • control : NOT USED
  • events : Receive events from source of pygame events
  • inbox : Default inbox, not currently used
  • notify : Receive requests for surfaces, overlays and events


  • outbox : NOT USED
  • signal : NOT USED

Methods defined here


You should be using the inbox/outbox interface, not these methods (except construction). This documentation is designed as a roadmap as to their functionalilty for maintainers and new component developers.

__init__(self, **argd)

x.__init__(...) initializes x; see x.__class__.__doc__ for signature


Check "notify" inbox for requests for surfaces, events and overlays and process them.



Main loop.

surfacePosition(self, surface)

Returns a suggested position for a surface. No guarantees its any good!

updateDisplay(self, display)

Render all surfaces and overlays onto the specified display surface.

Also dispatches events to event handlers.



Got a problem with the documentation? Something unclear that could be clearer? Want to help improve it? Constructive criticism is very welcome - especially if you can suggest a better rewording!

Please leave you feedback here in reply to the documentation thread in the Kamaelia blog.

-- Automatic documentation generator, 05 Jun 2009 at 03:01:38 UTC/GMT