PyOpenGL - A tutorial about shaders that doesn't work

Question

This is an example from: http://pyopengl.sourceforge.net/context/tutorials/shader_1.xhtml

It is creating a vbo, binging it, and running it with a shader, but somewhere along the way, it is not working properly. I searched a lot on the internet and didn't find any precise answers for my problem (the best pick I had was on this topic on StackOverflow : Why is this tutorial example of a shader not displaying any geometry as it is supposed to? but even if the author was working on the same tutorial, he didn't have the same problem and solved it by himself...)

from OpenGLContext import testingcontext
BaseContext = testingcontext.getInteractive()

from OpenGL.GL import *

from OpenGL.arrays import vbo

from OpenGLContext.arrays import *

from OpenGL.GL import shaders

class TestContext( BaseContext ):

    def OnInit( self ):
        VERTEX_SHADER = shaders.compileShader("""#version 330
        void main() {
                     gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
                     }""", GL_VERTEX_SHADER)

        FRAGMENT_SHADER = shaders.compileShader("""#version 330
        void main() {
                 gl_FragColor = vec4( 0, 3, 6, 1 );
                 }""", GL_FRAGMENT_SHADER)

        self.shader = shaders.compileProgram(VERTEX_SHADER,FRAGMENT_SHADER)

        self.vbo = vbo.VBO(
                        array( [
                            [  0, 1, 0 ],
                            [ -1,-1, 0 ],
                            [  1,-1, 0 ],
                            [  2,-1, 0 ],
                            [  4,-1, 0 ],
                            [  4, 1, 0 ],
                            [  2,-1, 0 ],
                            [  4, 1, 0 ],
                            [  2, 1, 0 ],
                        ],'f')
                      )

        def Render( self, mode):
            shaders.glUseProgram(self.shader)
        try:
            self.vbo.bind()

            try:
                glEnableClientState(GL_VERTEX_ARRAY);
                glVertexPointerf(self.vbo)
                glDrawArrays(GL_TRIANGLES, 0, 9)
            finally:
                self.vbo.unbind()
                glDisableClientState(GL_VERTEX_ARRAY);
        finally:
                shaders.glUseProgram(0)

if __name__ == "__main__":
    TestContext.ContextMainLoop()

Running this program from the windows command-line give me that error:

Traceback(most recent call last):
    File "openGL-test.py', line 70, in <module>
        TestContext.ContextMainLoop()
    File "C:\Python27\lib\site-package\openglcontext-2.2.0a2-py2.7.egg\OpenGLContext\glutcontext.py", line 159, in ContextMainLoop
        render = cls( *args, **named)
    File "C:\Python27\lib\site-package\openglcontext-2.2.0a2-py2.7.egg\OpenGLContext\glutcontext.py", line 35, in __init__
        glutInitDisplayMode( self.DISPLAYMODE )
    File "C:\Python27\lib\site-package\OpenGL\platform\baseplatform.py", line 384, in __call__
        self.__name__, self.__name__,
OpenGL.error.NullFunctionError: Attempt to call an undefined function glutInitDisplayMode, check for bool(glutInitDisplayMode) before calling

Any idea of what that means ? I have to precise, I began to learn Python two months ago, so I'm pretty newbie, even if I had to work it a lot for my internship period. (ho, and that's my first question on StackOverflow :)

Answer 1

It is failing because you don't have GLUT installed.

GLUT is the GL Utility Toolkit, a very widely used simple framework for creating OpenGL programs that runs on MS Windows, Macs, Linux, SGI, ... All the functions and constants have a glut or GLUT_ prefix, and glutInitDisplayMode is the usually the first function that gets called.

[ REMOVE INSTALLATION NOTES ]

OK, you've done the install and it still doesn't work. That means that while you have GLUT installed, the Python program can't load the GLUT DLL. Dynamic linking, oh joy.

Find where glut32.dll got installed.

A quick and dirty solution for a single program is to copy the glut DLL into the same directory as the program itself.

GLUT is 32 bit (AFAIK, unless you built it yourself) and this can be tricky if you have a 64 bit version of Windows 7. The advice online is that on 64 bit Windows a 32 bit DLL should be in C:\Windows\SysWoW64\ and a 64 bit DLL in C:\Windows\System32\

(Seriously. I have not swapped the two directory names by mistake.)

If that doesn't work, I'm out of ideas.

Answer 2

Some news ! Sorry for the delay, had to work on a huge piece of mathematical theory for school this week.

So, as Hugh Fisher asked me, I checked where glut32.dll was installed. And what a surprise when I found out it wasn't installed... anywhere ! So I downloaded glut32.dll and put it into c:\Windows\System32\ at first but, as it didn't work, I put it into Windows\SysWOW64\ instead. And... it works ! So the solution seems to be:

• find where glut32.dll (beware, there is a glu32.dll in the System32 file, not the same!)
• if no such file exists, download it
• put the downloaded glut32.dll in c:\Windows\System32\ if you have a 32 bit Windows
• put it in c:\Windows\SysWOW64\ if 64 bit Windows

Thanks to Hugh Fisher for the solution.