Re: [PyOpenGL-Users] best way to set up matrices and vertex arrays?

[Greg E. <gre...@ca...>]

Kolja Kaehler wrote:

> -          Row-major vs. column-major matrices. With the default 
> row-major layout used by numpy, I always have to pass in matrices as the 
> transpose of what I expect. I found out I can create numpy arrays with 
> ‘F’ order, but I still have to transpose matrices I get back from 
> PyOpenGL, it seems.

You might like to consider just working with the transposed
arrays as they are.

Thinking about this recently, I realised that the OpenGL
order may actually be more convenient for some things, such
as transforming an array of vertices. With a transposed
matrix, you can do A*M, where A is an n-by-4 array. With
a non-transposed matrix, you would have to do M*A and
transpose A into a 4-by-n array.

> -          What’s a good way to build a dynamically growing vertex 
> array? ... Currently, I am setting up an array with 
> shape(n,3) and concatenate another array of length 3 to it. ... I 
> believe it’s always making a copy.

Yes, that will be horribly inefficient.

I would build up a list of vertices first, and then convert
the whole list to an array in one go.

> To transform a 3D vector with a 4x4 matrix, I have to append an 
> extra 1.0 element, do the multiplication, and then slice off the 4^th 
> element again.

Another way is to work with 4-element vectors throughout.

-- 
Greg