Re: [PyOpenGL-Users] Problems with simple pyopengl program

[James G. <ja...@ja...>]

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 <mcf...@vr...>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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