Re: Problems with simple pyopengl program

On 12-02-22 10:31 PM, James Gao wrote:
> 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?
Yeah, though I'm tempted to just disallow that functionality (int/float 
as an array) when the data-type is a GLvoidp (which should cover 
essentially all of the pointer-as-offset types, IIRC)... or maybe just 
disable it globally, as it really isn't all *that* useful most of the time.

Have fun,
Mike
>
>
> On Wed, Feb 22, 2012 at 6:58 PM, Mike C. Fletcher 
> <[email protected] <mailto:[email protected]>> 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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>


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


------------------------------------------------------------------------------
Virtualization & Cloud Management Using Capacity Planning
Cloud computing makes use of virtualization - but cloud computing 
also focuses on allowing computing to be delivered as a service.
http://www.accelacomm.com/jaw/sfnl/114/51521223/
_______________________________________________
PyOpenGL Homepage
http://pyopengl.sourceforge.net