Re: [PyOpenGL-Users] mixing C++ and python w/ opengl

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

On 11-01-25 06:48 PM, Philip Winston wrote:
...
>
>     > Rather than pull it into Python and then push it
>     > back with pyopengl, it seems like we could just draw it from C,
>     if that
>     > is allowed.
>
>     well, I don't know that I'd do it for this reason -- if you pull/push
>     the data as numpy arrays, you can do all that without data copying, so
>     keeping it in Python may be fine.
>
>
> You might be right.
>
> How do you completely avoid the copy?  I do something really 
> simple/dumb when right now when I need to return an array from C to 
> Python.  I do use numpy, but I do the allocation in Python and then 
> hand the empty array to C to copy the values into.
By default, numpy arrays only copy if they need to have their 
data-format changed.  There's a flag in OpenGL.__init__ which, if set on 
import, will raise errors when that copying occurs.  You can do the same 
by registering an array data-format handler for your C-provided types, 
but Numpy is probably a better/easier option.  Under the covers, 
PyOpenGL is examining the type of the numpy array and, if it is 
compatible, just pulling out the data-pointer from the underlying memory 
area.  Your data-array class could do the same thing, but again, it is 
probably easier to just use Numpy for this kind of work.
>
> I saw some stuff about defining an allocator but it looked complicated.
>
> I wonder if my simplistic approach if the copy would hurt me.  I 
> wonder if I should be using a better no-copy approach instead.
Moving the drawing to C/C++ is certainly supported and easy if you 
already have the C/C++ rendering code.  Avoiding copying is *always* a 
good approach to speeding things up.
> Anyway probably I should start by keeping drawing in Python and 
> if/when I measure a real performance problem consider pushing it to C. 
>  This is how we operate with other stuff, resorting to C only to solve 
> a specific performance issue.
Sounds like a good plan.  Good luck,
Mike

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