Re: [PyOpenGL-Users] Pointer functions copying memory.

[Mike C. F. <mcf...@ro...>]

The biggest problem I see is that the buffer API is loosely considered 
deprecated.  BTW I could've sworn that we were already using the 
PyArray_ functions to get contiguous array pointers...

See the NUMERIC_PyObject_As macro in interface_util.c, as far as I'm 
aware, this should be getting used everywhere.  However, if I understand 
the mechanism behind the 
(PyArrayObject*)PyArray_ContiguousFromObject(source, TYPECODE | 
SAVESPACEBIT, 0, 0); function, it's going to do a copy of the source 
array is not contiguous, which would give us the copying overhead we're 
seeing.

What I would prefer to see (instead of using a pseudo-deprecated API, or 
using functions to access the non-contiguous array (which likely won't 
work for OpenGL, as I believe it requires a true contiguous array)) is a 
function that, given a Numeric array, returns a contiguous version of 
that array to Python (or raises a memory error if it's not possible). 
 That should, if I understand correctly, make further 
PyArray_ContiguousFromObject calls on the _resulting_ array null 
operations.  The "problem" being that the current code doesn't modify 
the Python pointer to the array to point to the new, contiguous array 
(and obviously it shouldn't do so in the middle of an OpenGL call), so 
the effort isn't saved between rendering passes.

Just my thoughts,
Mike


Rene Dudfield wrote:

>Hi,
>
>I had a look at the pointer functions and it appears
>they copy memory before passing it to the gl function,
>making them quite slow.
>
>I was thinking of using the buffer api instead.
>
>http://python.org/doc/current/api/bufferObjects.html
>
>Not sure if numeric supports it.  If it doesn't I'll
>use the PyArray_ContiguousFromObject functions.
>
>
>Any thoughts on this?  Any compatibility problems with
>the buffer api?
>
>  
>
...

_______________________________________
  Mike C. Fletcher
  Designer, VR Plumber, Coder
  http://members.rogers.com/mcfletch/