使用GTKGLArea时，为什么在PyOpenGL中未定义glGenVertexArrays

Question

我在下面有下面的测试代码，我试图让一个基本的opengl Gtk3 GLArea示例工作。

下面的错误当前是我的关键点，从我所读到的这可能意味着这些功能不可用于上下文但是阅读GLArea它似乎并没有让你选择上下文和声音它应该默认为正确的。

问题可能出在GLArea或PyOpenGL上，遗憾的是我可以很好的所有例子目前在C中都可以获得一个在python中运行的基本示例。

无论如何花了很多时间试图解决这个问题所以如果任何人都可以帮助过去至少这个错误将是很好的。

Traceback (most recent call last):
File "gtkglarea.py", line 91, in on_configure_event
self.vertex_array_object = glGenVertexArrays(1)
File "/usr/lib/python3/dist-packages/OpenGL/platform/baseplatform.py", line 407, in call
self.name, self.name,
OpenGL.error.NullFunctionError: Attempt to call an undefined function glGenVertexArrays, check for bool(glGenVertexArrays) before calling

例如，它也在gist https://gist.github.com/olymk2/5b3e49ac83130e580bd9983f2e5d49c3上

#!/usr/bin/python
import os
import sys

from OpenGL.GLU import *
from OpenGL import GLX
from OpenGL import GL as GL
from ctypes import *
import gi
gi.require_version('Gtk', '3.0')
from gi.repository import Gtk, Gdk

from OpenGL.arrays import vbo
from OpenGL.GL import shaders
from OpenGL.raw.GL.ARB.vertex_array_object import glGenVertexArrays, \
                                                  glBindVertexArray

from numpy import array
import numpy as np

VERTEX_SHADER = """
    #version 330
    in vec4 position;
    void main()
    {
        gl_Position = position;
    }"""

FRAGMENT_SHADER = """
    #version 330
    out vec4 fragColor;
    void main()
    {
        fragColor = vec4(1.0, 0.0, 0.0, 1.0);
    }
    """


class application_gui:
    """Tutorial 01 Create and destroy a window"""
    # glwrap = gtkglarea()
    def __init__(self):
        self.window = Gtk.Window()
        self.canvas = Gtk.GLArea()
        self.canvas.set_required_version(3, 3)
        self.test_features()

        self.vertices = [
            0.6,  0.6, 0.0, 1.0,
            -0.6,  0.6, 0.0, 1.0,
            0.0, -0.6, 0.0, 1.0]

        self.vertices = np.array(self.vertices, dtype=np.float32)

        self.canvas.connect('realize', self.on_configure_event)
        self.canvas.connect('render', self.on_draw)
        self.canvas.set_double_buffered(False)

        self.window.connect('delete_event', Gtk.main_quit)
        self.window.connect('destroy', lambda quit: Gtk.main_quit())

        self.window.add(self.canvas)
        self.window.show_all()

        self.on_configure_event(self.canvas)

    def test_features(self):
        print('Testing features')
        print('glGenVertexArrays Available %s' % bool(glGenVertexArrays))
        print('Alpha Available %s' % bool(self.canvas.get_has_alpha()))
        print('Depth buffer Available %s' % bool(self.canvas.get_has_depth_buffer()))



    def on_configure_event(self, widget):
        print('realize event')

        widget.make_current()
        # widget.attach_buffers()
        context = widget.get_context()

        print('is legacy context %s' % Gdk.GLContext.is_legacy(context))
        print('configure errors')
        print(widget.get_error())


        vs = shaders.compileShader(VERTEX_SHADER, GL.GL_VERTEX_SHADER)
        fs = shaders.compileShader(FRAGMENT_SHADER, GL.GL_FRAGMENT_SHADER)
        self.shader = shaders.compileProgram(vs, fs)

        self.vertex_array_object = glGenVertexArrays(1)
        GL.glBindVertexArray( self.vertex_array_object )

        # Generate buffers to hold our vertices
        self.vertex_buffer = GL.glGenBuffers(1)
        GL.glBindBuffer(GL.GL_ARRAY_BUFFER, self.vertex_buffer)

        # Get the position of the 'position' in parameter of our shader and bind it.
        self.position = GL.glGetAttribLocation(self.shader, 'position')
        GL.glEnableVertexAttribArray(self.position)

        # Describe the position data layout in the buffer
        GL.glVertexAttribPointer(self.position, 4, GL.GL_FLOAT, False, 0, ctypes.c_void_p(0))

        # Send the data over to the buffer
        GL.glBufferData(GL.GL_ARRAY_BUFFER, 48, self.vertices, GL.GL_STATIC_DRAW)

        # Unbind the VAO first (Important)
        GL.glBindVertexArray( 0 )

        # Unbind other stuff
        GL.glDisableVertexAttribArray(self.position)
        GL.glBindBuffer(GL.GL_ARRAY_BUFFER, 0)

        print('errors')
        print(widget.get_error())

        return True

    def on_draw(self, widget, *args):
        print('render event')
        print(widget.get_error())
        #Create the VBO

        widget.attach_buffers()

        GL.glClear(GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT)
        GL.glUseProgram(self.shader)

        GL.glBindVertexArray( self.vertex_array_object )
        GL.glDrawArrays(GL.GL_TRIANGLES, 0, 3)
        GL.glBindVertexArray( 0 )

        GL.glUseProgram(0)
        glFlush()
        return True

application = application_gui()
Gtk.main()

Answer 1

对我来说，问题似乎与在Wayland下运行有关。看起来如果PyOpenGL在Wayland下运行并且运行了X11服务器，它将使用GLX而不是Wayland的EGL支持。关于GtkGLArea如何设置GL上下文的方法意味着GLX可以工作但没有任何GL扩展，其中包括VAO。这似乎是PyOpenGL中的一个错误。

有两种方法可以解决这个问题：

1. 设置PYOPENGL_PLATFORM以强制PyOpenGL使用EGL而不是GLX。 例如。在导入OpenGL之前：

   if 'WAYLAND_DISPLAY' in os.environ and 'PYOPENGL_PLATFORM' not in os.environ:
       os.environ['PYOPENGL_PLATFORM'] = 'egl'

2. 取消设置WAYLAND_DISPLAY以强制Gtk使用GLX而不是EGL。 例如。在导入Gtk之前：

   if 'WAYLAND_DISPLAY' in os.environ:
       del os.environ['WAYLAND_DISPLAY']

Answer 2

下面的工作是完整的工作示例，在@derhass的评论后我做了一些搜索并找到了Gdk.Screen为什么在我之前发现的我不知道的例子中没有使用它。

拼图中缺少的是这3行

screen = Gdk.Screen.get_default()
visual = Gdk.Screen.get_rgba_visual(screen)
self.window = Gtk.Window()
Gtk.Widget.set_visual(self.window, visual)

完整的工作样本，应该在一个看起来像这样的窗口中显示您的基本三角形。

#!/usr/bin/python
# noqa: E402
import gi 
gi.require_version('Gtk', '3.0')
import numpy as np
from gi.repository import Gtk, Gdk
from OpenGL.GLU import *
from OpenGL import GL as GL

from OpenGL.GL import shaders
from OpenGL.raw.GL.ARB.vertex_array_object import glGenVertexArrays, \
                                                  glBindVertexArray

# from numpy import array

VERTEX_SHADER = """
    #version 330
    in vec4 position;
    void main()
    {
        gl_Position = position;
    }"""

FRAGMENT_SHADER = """
    #version 330
    out vec4 fragColor;
    void main()
    {
        fragColor = vec4(1.0, 0.0, 0.0, 1.0);
    }
    """


class application_gui:
    """Tutorial 01 Create and destroy a window"""
    # glwrap = gtkglarea()
    def __init__(self):
        screen = Gdk.Screen.get_default()
        visual = Gdk.Screen.get_rgba_visual(screen)

        print('is composite %s' % Gdk.Screen.is_composited(screen))

        self.window = Gtk.Window()
        Gtk.Widget.set_visual(self.window, visual)
        self.canvas = Gtk.GLArea()
        self.canvas.set_required_version(3, 3)
        self.test_features()

        self.vertices = [
            0.6,  0.6, 0.0, 1.0,
            -0.6,  0.6, 0.0, 1.0,
            0.0, -0.6, 0.0, 1.0]

        self.vertices = np.array(self.vertices, dtype=np.float32)

        self.canvas.connect('realize', self.on_configure_event)
        self.canvas.connect('render', self.on_draw)
        self.canvas.set_double_buffered(False)

        self.window.connect('delete_event', Gtk.main_quit)
        self.window.connect('destroy', lambda quit: Gtk.main_quit())

        self.window.add(self.canvas)
        self.window.show_all()

    def test_features(self):
        print('Testing features')
        print('glGenVertexArrays Available %s' % bool(glGenVertexArrays))
        print('Alpha Available %s' % bool(self.canvas.get_has_alpha()))
        print('Depth buffer Available %s' % bool(self.canvas.get_has_depth_buffer()))

    def on_configure_event(self, widget):
        print('realize event')
        widget.make_current()
        print(widget.get_error())

        vs = shaders.compileShader(VERTEX_SHADER, GL.GL_VERTEX_SHADER)
        fs = shaders.compileShader(FRAGMENT_SHADER, GL.GL_FRAGMENT_SHADER)
        self.shader = shaders.compileProgram(vs, fs)

        # Create a new Vertex Array Object
        self.vertex_array_object = GL.glGenVertexArrays(1)
        GL.glBindVertexArray(self.vertex_array_object )

        # Generate a new array buffers for our vertices
        self.vertex_buffer = GL.glGenBuffers(1)
        GL.glBindBuffer(GL.GL_ARRAY_BUFFER, self.vertex_buffer)

        # Get position variable form the shader and store
        self.position = GL.glGetAttribLocation(self.shader, 'position')
        GL.glEnableVertexAttribArray(self.position)

        # describe the data layout
        GL.glVertexAttribPointer(self.position, 4, GL.GL_FLOAT, False, 0, ctypes.c_void_p(0))

        # Copy data to the buffer
        GL.glBufferData(GL.GL_ARRAY_BUFFER, 48, self.vertices, GL.GL_STATIC_DRAW)

        # Unbind buffers once done
        GL.glBindVertexArray( 0 )
        GL.glDisableVertexAttribArray(self.position)
        GL.glBindBuffer(GL.GL_ARRAY_BUFFER, 0)

        return True

    def on_draw(self, widget, *args):
        print('render event')
        print(widget.get_error())

        # clear screen and select shader for drawing
        GL.glClear(GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT)
        GL.glUseProgram(self.shader)

        # bind and draw vertices
        GL.glBindVertexArray(self.vertex_array_object)
        GL.glDrawArrays(GL.GL_TRIANGLES, 0, 3)
        GL.glBindVertexArray(0)

        GL.glUseProgram(0)
        GL.glFlush()
        return True

application = application_gui()
Gtk.main()