Ahh, that did it, thank you so much! I had written a much larger program based on a shader tutorial. I spent the last day and a half slowly paring down the program until I got to that stub. I copied all of it to C, saw that it worked, and finally had to ask someone...

Perhaps a very large note in the documentation would be good? 

-James

On Wed, Feb 22, 2012 at 6:58 PM, Mike C. Fletcher <mcfletch@vrplumber.com> wrote:
On 12-02-22 07:47 PM, James Gao wrote:
> Hi everyone,
> I'm trying to get a very very simple pass-through shader to work in
> pyopengl. I compiled and tested a simple C program, available here:
> http://pastebin.com/FGVxUUXH
> This program works exactly as expected -- a red plane is drawn,
> completely covering the screen.
>
> I tried to make the *exact* duplicate of this C program here:
> http://pastebin.com/dYbbXTY1
> This apparently does not work. Only the gray glClear color is
> displayed, and the two triangles are never drawn.
>
> Any insight into why this isn't working?

You need to modify the calls which are using voidp offsets to explicitly
create GLvoidp instances, the integer 0 values are being interpreted as
single-value arrays and the result is a useless offset:

    glVertexAttribPointer( posidx, 2, GL_FLOAT, GL_FALSE, 4*2, GLvoidp(0))

    # Draw the two triangles
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebuf);
    glDrawElements(
        GL_TRIANGLES,           # mode
        6,           # count
        GL_UNSIGNED_SHORT,      # type
        GLvoidp(0)                       # element array buffer offset
    )

This is a mis-feature of the wrapping in PyOpenGL allowing you to pass
in an integer where an array is expected.

HTH,
Mike

--
________________________________________________
  Mike C. Fletcher
  Designer, VR Plumber, Coder
  http://www.vrplumber.com
  http://blog.vrplumber.com


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