glx opengl gtk python and alpha channels / blending

Question

I have the example code below, simplified from a larger project. I have been trying to make alpha channels work i have enabled blending and written a similar example using pygame which works. How ever setting up opengl to work with a glx context seems to stop blending from working, i have a feeling i need to enabel some parameter to the gl context setup but have not been able to find out what that parameter is.

Any suggestions on why this is not working, i have tried on two different machines one with high end radeon and another with an intel graphics card both do the same however.

#blending is not working any ideas why ? 
import sys
from OpenGL.GL import *
from OpenGL.GLU import *
from OpenGL import GLX
from OpenGL.raw._GLX import struct__XDisplay
from OpenGL import GL
from ctypes import *

import Xlib
from Xlib.display import Display
from gi.repository import Gtk, GdkX11, Gdk


class gtkgl:
    """ these method do not seem to exist in python x11 library lets exploit the c methods """
    xlib = cdll.LoadLibrary('libX11.so')
    xlib.XOpenDisplay.argtypes = [c_char_p]
    xlib.XOpenDisplay.restype = POINTER(struct__XDisplay)
    xdisplay = xlib.XOpenDisplay("")
    display = Xlib.display.Display()
    attrs = []

    xwindow_id = None
    width = height = 200

    def __init__(self):
        """ lets setup are opengl settings and create the context for our window """
        self.add_attribute(GLX.GLX_RGBA, True)
        self.add_attribute(GLX.GLX_RED_SIZE, 1)
        self.add_attribute(GLX.GLX_GREEN_SIZE, 1)
        self.add_attribute(GLX.GLX_BLUE_SIZE, 1)
        self.add_attribute(GLX.GLX_ALPHA_SIZE, 1)
        self.add_attribute(GLX.GLX_DOUBLEBUFFER, 0)


        glClearDepth(1.0)
        glEnable(GL_DEPTH_TEST)
        glEnable(GL_BLEND)
        glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
        glShadeModel(GL_SMOOTH)
        glDepthFunc(GL_LEQUAL)
        glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST)
        glEnable(GL_COLOR_MATERIAL)
        glEnable(GL_LIGHTING)
        glEnable(GL_LIGHT0)        
        glLight(GL_LIGHT0, GL_POSITION,  (0, 1, 1, 0)) 


        xvinfo = GLX.glXChooseVisual(self.xdisplay, self.display.get_default_screen(), self.get_attributes())
        configs = GLX.glXChooseFBConfig(self.xdisplay, 0, None, byref(c_int()))
        self.context = GLX.glXCreateContext(self.xdisplay, xvinfo, None, True)

    def add_attribute(self, setting, value):
        """just to nicely add opengl parameters"""
        self.attrs.append(setting)
        self.attrs.append(value)

    def get_attributes(self):
        """ return our parameters in the expected structure"""
        attrs = self.attrs + [0, 0]
        return (c_int * len(attrs))(*attrs)

    def configure(self, wid):
        """  """
        self.xwindow_id = GdkX11.X11Window.get_xid(wid)
        if(not GLX.glXMakeCurrent(self.xdisplay, self.xwindow_id, self.context)):
            print 'failed'
        glViewport(0, 0, self.width, self.height)

    def draw_start(self):
        """make cairo context current for drawing"""
        if(not GLX.glXMakeCurrent(self.xdisplay, self.xwindow_id, self.context)):
            print "failed"

    def draw_finish(self):
        """swap buffer when we have finished drawing"""
        GLX.glXSwapBuffers(self.xdisplay, self.xwindow_id)

    def test(self):
        """Test method to draw something so we can make sure opengl is working and we can see something"""
        self.draw_start()

        glClearColor(0.0, 0.0, 0.0, 0.0)
        glClear(GL_COLOR_BUFFER_BIT)
        glBegin(GL_TRIANGLES)
        glIndexi(0)
        glColor4f(1.0, 0.0, 0.0, 0.2)
        glVertex2i(0, 1)
        glIndexi(0)
        glColor4f(0.0, 1.0, 0.0, 0.2)
        glVertex2i(-1, -1)
        glIndexi(0)
        glColor4f(0.0, 0.0, 1.0, 1.0)
        glVertex2i(1, -1)
        glEnd()

        self.draw_finish()


class gui():
    glwrap = gtkgl()

    def __init__(self):
        self.window = Gtk.Window()
        self.window.realize()
        self.window.resize(self.glwrap.width, self.glwrap.height)
        self.window.set_resizable(True)
        self.window.set_reallocate_redraws(True)
        self.window.set_title("GTK3 with opengl")
        self.window.connect('delete_event', Gtk.main_quit)
        self.window.connect('destroy', lambda quit: Gtk.main_quit())

        self.drawing_area = Gtk.DrawingArea()
        self.drawing_area.connect('configure_event', self.on_configure_event)
        self.drawing_area.connect('draw', self.on_draw)
        self.drawing_area.set_double_buffered(False)
        self.drawing_area.set_size_request(self.glwrap.width, self.glwrap.height)

        self.window.add(self.drawing_area)
        self.window.show_all()

    def on_configure_event(self, widget, event):
        self.glwrap.configure(widget.get_window())
        return True

    def on_draw(self, widget, context):
        self.glwrap.test()


def main():
    g = gui()
    Gtk.main()

if __name__ == '__main__':
    main()

Answer 1

It's not the OpenGL context missing something (at the point of creation I mean). You're simply not enabling blending. You need to add a glEnable(GL_BLEND); before drawing primitives that require blending.

BTW: Using 1 bit as minimum requirement for RGB channels can yield to undesired results. Use at least 5 bits (for 16 bit displays) or better yet 8 bits. Also you don't need an alpha channel on the main framebuffer for blending to work. So unless you want to create transparent windows on a compositor, then you should use 0 alpha bits on the window's framebuffer.