Re: [PyOpenGL-Users] Having a problem with glBufferData

[René D. <re...@gm...>]

Hi,

remember that you can use the OpenGL.raw.GL calls... which are more
direct wrappers.  Sometimes easier to use if you have a bug/can't
figure out how to use the normal python wrappers.  Of course then you
need to know ctypes... but that's not too hard.

cheers,


On Sun, Aug 30, 2009 at 9:18 PM, Gijs<in...@bs...> wrote:
> Hey List,
>
> I'm trying to use PBOs for the first time so I'm not completely aware of
> what I'm doing with the code I found on this site. One thing I do know is
> that the code I can execute in C, I cannot execute in Python. This has to do
> with a piece of code that makes use of glBufferData and its 4th argument,
> namely "size".
>
> The C code:
> glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, thebuffer);
> glBufferData(GL_PIXEL_PACK_BUFFER_ARB,4*sizeof(float), NULL,
> GL_STREAM_READ);
> glReadPixels (0, 0, 1, 1, GL_RGBA, GL_FLOAT, 0);
> void* mem = glMapBuffer(GL_PIXEL_PACK_BUFFER_ARB, GL_READ_ONLY);
> assert(mem);
> glUnmapBuffer(GL_PIXEL_PACK_BUFFER_ARB);
> glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, 0);
>
> Python Code:
> glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, thebuffer)
> glBufferData(GL_PIXEL_PACK_BUFFER_ARB,None, GL_STREAM_READ)
> glReadPixels (0, 0, 1, 1, GL_RGBA, GL_FLOAT, 0)
> mem = glMapBuffer(GL_PIXEL_PACK_BUFFER_ARB, GL_READ_ONLY)
> glUnmapBuffer(GL_PIXEL_PACK_BUFFER_ARB)
> glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, 0)
>
> Since I cannot specify 4 arguments for glBufferData, as I can do in C, the
> code I execute in Python is doing something different than the C version.
> This results in an OpenGL error 1282 (invalid operation) when I call
> glReadPixels. I guess when the interface for this function was written, it
> was never expected to be called like this. A normal call would supply a
> variable, and PyOpenGL would be able to determine the size, so the size
> argument wouldn't be needed. Too bad in a case like this, it is needed, as
> far as I can see. Or is there some other way of accessing this function?
>
> Regards, Gijs
>
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