Archive for pyglet

Using ARRAY_BUFFER’s in PyOpenGL

Posted in How To, Programming, PyGLy with tags , , , , on 2013/02/16 by Adam Griffiths

I’m in the process of converting my code from Pyglet GL to PyOpenGL.
In doing so, my VBO objects stopped rendering.

It turns out the problem is glVertexAttribPointer.
The Pyglet GL version takes the last parameter (offset) as a number. I set this to 0 for arrays with no offset.

glVertexAttribPointer( in_position, 3, GL_FLOAT, GL_FALSE, 0, 0)

It seems that PyOpenGL expects the pointer value by absolute instead of relative.
The solution is to pass None instead of 0.

glVertexAttribPointer( in_position, 3, GL_FLOAT, GL_FALSE, 0, None)

If you have an actual offset to pass, you need to convert to a ctypes c_void_p (void*).
http://stackoverflow.com/questions/11132716/how-to-specify-buffer-offset-with-pyopengl

glVertexAttribPointer( in_position, 3, GL_FLOAT, GL_FALSE, 0, ctypes.c_void_p(offset))

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PyGLy steps into the future

Posted in Development, PyGLy, Twisted Pair with tags , , , , , on 2012/09/21 by Adam Griffiths

I’ve been working quite heavily on PyGLy for the last few weeks and I’m incredibly pleased to announce that PyGLy is now OpenGL 3 clean!

It took more work than I hoped. Not because of PyGLy (it was already pretty good), but Pyglet’s OpenGL Core (3+) support on OS-X, is well… broken.
I had to integrate a patch written by someone else and patch out 2 of the window event handlers.
The main reason for this is that OpenGL Core on OS-X is limited to 3.2, and is Core only (no legacy compatibility).
These changes can be found in my Github repository.

Pyglet isn’t without it’s problems. It is quite heavy weight in places. There is no support for float or 1D textures.
Other problems are it’s usage of legacy calls. These are scattered throughout the code base and prevent me from using even the Label or VertexList classes.
I would LOVE to help with the development of Pyglet… but I find the code… very confusing.
It’s got a fair amount of abstraction. Tracing even a vertex buffer blows my mind.

Regardless, I hope these issues will be fixed soon.

OpenGL and GLSL support in OS-X

Posted in Twisted Pair with tags , , , , on 2012/08/13 by Adam Griffiths

I had difficulty finding the supported OpenGL and GLSL versions in OS-X.
Using Pyglet, I get errors trying to use versions GLSL 1.30 and above. Printing out the version returns 1.20.

from ctypes import *
from pyglet.gl import *

print "OpenGL version", gl_info.get_version()

plain = string_at(glGetString(GL_SHADING_LANGUAGE_VERSION)).split(' ')[0]
major, minor = map(int, plain.split('.'))
version = major*100 + minor
print "GLSL Version",version

Looking around I found this information.
Mac OS-X OpenGL Support

Legacy would infer the “Fixed Function Pipeline” and Core would be modern OpenGL.
So it seems that legacy OpenGL (normal Pyglet) is stuck with GLSL 1.20 and Core has 1.50.

This code can be found on the Pyglet source repository that enables OpenGL 3 (Core).
Enable OpenGL 3 in Pyglet

But the ouput I get is not correct.

OpenGL version 2.1 ATI-1.0.25
GLSL Version 120

According to this conversation, it appears that Pyglet ignores the OpenGL version on OS-X currently.

Initial release of PyGLy

Posted in Development, Programming, Twisted Pair with tags , , , , on 2012/03/07 by Adam Griffiths

It’s a pretty big day for us, as I’m pushing my labor of love, PyGLy, to GitHub.

PyGLy is a 3D framework developed in pure python.

I’ve been dismayed at the state of game frameworks on Python.

There are a large number of quality 3D engines and frameworks out there. However, there are serious problems with the ‘engines’ out there that have Python bindings.

  • Not truly cross-platform (this is Python FFS!).
  • Not free.
  • Not maintained.
  • No documentation (the worst culprit).
  • Bindings are 2nd class citizens and you still need to code C/C++/Whatever.
  • Don’t work with latest versions of code.

Most engines have bindings created by the community. The problem is these are quickly dumped when the person moves on.

Python only 3D engines seem… well… stagnant.

  • PySoya and PySoy seem to be seething at each other but not really producing much.
  • PyGame is just SDL in disguise.
  • The rest… well they all 404 now.

For the most part, 3D game development on Python is dead.

So, behind the scenes, I’ve been writing my own 3D framework for Python, PyGLy.

“Framework” is an important word there. PyGLy does not force any one methodology on you. PyGLy simply provides functionality to wrap common functionality. Windows, Viewports, Scene Graph Nodes, Cameras. It’s up to you to put them together how you want.

Obviously some things are going to be coupled together. But for the most part, PyGLy just gets out of the way.

At the moment PyGLy is quite small, but it is in active development and already has features that may interest some.

I think the best case for it at the moment is for people wanting to rapidly prototype in 3D but not be abstracted from the rendering process. PyGLy lets you forget about the scene graph and just concentrate on rendering your objects. Rendering is performed via callbacks. You can make any OpenGL call you want in these callbacks.

PyGLy is the foundation of our Python 3D work, so expect it to be actively developed going forward.

The following are some of the things that we’re wanting to add in the future:

  • Shadowing.
  • Scene management (Octree, etc).
  • Cocos2D integration (CCLayer).
  • Separate OpenGL 3+ path.

As we’ve said before, Twisted Pair are true believers of Open Source, so you can find PyGLy on our GitHub repository under a very liberal license.

Pyglet mouse events and rendering

Posted in Development, How To, Programming with tags , , , , on 2011/06/28 by Adam Griffiths

The Problem

I added mouse event handlers to my Pyglet application recently. I found when I moved the mouse over the window, my rendering started to create “ghost” images.

I finally found the solution hidden in the docs.

The pyglet application event loop dispatches window events (such as for mouse and keyboard input) as they occur and dispatches the on_draw event to each window after every iteration through the loop.

So every mouse move (or any other event) triggers Pyglet to call “on_draw”.

But because I’m controlling my own render loop at 60Hz, I didn’t see a need to hook into this event. So I assume Pyglet is attempting to render the scene itself, and it’s failing miserably.

This is really bad design! What if I have lots of events that are seperate? Looks like Pyglet is going to hammer the “on_draw” event.

The Solution?

Well the basic solution is to ensure you’ve hooked into the “on_draw” event and just connect it to your render call. Don’t connect it to your game update logic or you will end up updating everything.

But…

This means your frame rate will vary depending on user input, and may even end up running balls out. Which could turn a simple game into a system hog. My basic application goes from 1% (of 2 cores on a dual core system), to 20% with the mouse moving.

It also means that you need to decouple the rendering from the system update, as each event you have scheduled will trigger an “on_draw” event. If you don’t decouple them, you will render each frame twice!

The Proper Solution?

We need to over-ride the “EventLoop.idle” method as mentioned in the docs.

The code without “on_draw” looks like this:

def idle( self ):
    """An alternate idle loop than Pyglet's default.

    By default, pyglet calls on_draw after EVERY batch of events
    which without hooking into, causes ghosting
    and if we do hook into it, it means we render after every event
    which is REALLY REALLY BAD
    http://www.pyglet.org/doc/programming_guide/the_application_event_loop.html
    """
    pyglet.clock.tick( poll = True )
    # don't call on_draw
    return pyglet.clock.get_sleep_time( sleep_idle = True )

def patch_idle_loop():
    """Replaces the default Pyglet idle look with the :py:func:`idle` function in this module.
    """
    # check that the event loop has been over-ridden
    if pyglet.app.EventLoop.idle != idle:
        # over-ride the default event loop
        pyglet.app.EventLoop.idle = idle

The “on_draw” function also calls pyglet.window.flip() for us, so now we need to do that after our rendering. So add the following (obviously you need to change the window variable depending on what you’ve called it):

# switch out the default idle function for ours
patch_idle_loop()

def render( self ):
    # do render here
    # flip the buffers
    self.window.flip()

And we’re done! No more superfluous “on_draw” events and my simple application no longer spikes the CPU usage when the mouse is moved!

Registering Event Handlers in Pyglet

Posted in Development, How To, Programming with tags , , , , , on 2011/06/25 by Adam Griffiths

The Problem and Pyglet’s own solutions

Pyglet’s documentation suggests a number of methods to receive events.

The recommended method of using @ decorators works for global methods where the event object is known. But if its for a class method or the event object is passed in later, this will not work.

The alternative is to simply over-write the existing handler with something like

window.on_resize = self.on_resize

Unfortunately most of them end up with the following error:

window.set_handler( window.on_key_release, self.on_key_release )
AttributeError: 'Win32Window' object has no attribute 'on_key_release'

This discussion on the developer list explains it. This method only works when the platform’s window class has an existing method to handle the event. And not all events are handled by default, so when you come across this, BOOM!

Even then, when it works this is also a double edged sword. The existing handlers are there for a reason! For example, if you over-write the on_resize method of Window your application will no longer draw (took me a while to figure this out).

So yes, Pyglet’s documentation is really, REALLY, asking for trouble.

The Proper Solution?

Use the “push_handlers” method.

Pyglet automatically detects a method with the event’s name and dispatches the event.
So we can just add methods to our class and we’ll automatically receive the events.

class Test:
  def attachToWindow( self, window ):
    window.push_handlers( self )

  def on_key_press( self, symbol, modifiers ):
    # method name matches the 'on_key_press' event!
    print "Keypress"

Or we can manually specify which events we care about.
If we do this, we must specify the actual function that receives the event.

class Test:
  def attachToWindow( self, window ):
    window.push_handlers( on_key_press = self.on_key_press )

  def on_key_press( self, symbol, modifiers ):
    # method name matches the 'on_key_press' event!
    print "Keypress"
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