Question

My vertices are interleaved in a numpy array (dtype = float32) like this: … tu, tv, nx, ny, nz, vx, vy, vz, …

When rendering, I’m calling gl*Pointer() like this (I have enabled the arrays before):

stride = (2 + 3 + 3) * 4
glTexCoordPointer( 2, GL_FLOAT, stride, self.vertArray )
glNormalPointer( GL_FLOAT, stride, self.vertArray + 2 )
glVertexPointer( 3, GL_FLOAT, stride, self.vertArray + 5 )
glDrawElements( GL_TRIANGLES, len( self.indices ), GL_UNSIGNED_SHORT, self.indices )

The result is that nothing renders. However, if I organize my array so that the vertex position is the first element ( … vx, vy, vz, tu, tv, nx, ny, nz, … ) I get correct positions for vertices while rendering but texture coords and normals aren’t rendered correctly.

This leads me to believe that I’m not setting the pointer offset right. How should I set it? I’m using almost the exact same code in my other app in C++ and it works.

Answer 1

In python, you can’t do pointer arithmetic. What you’re trying to do only works for C/C++.

With normal Python list:

>>> array = [1, 2, 3, 4]
>>> array
[1, 2, 3, 4]
>>> array + 2
Traceback (most recent call last):
  File "<input>", line 1, in <module>
TypeError: can only concatenate list (not "int") to list

With numpy arrays:

>>> import numpy
>>> a = numpy.array([1, 2, 3])
>>> a + 2
array([3, 4, 5])

See how neither does what you want: starting the array at a certain position.

I think you have basically two options:

1. Don’t use interleaved arrays. This does have one advantage: when you only need to update the vertices (like in bone animations), you don’t need to update the texture coordinates.
2. Using slices might work for you.

Like this:

>>> a = numpy.array(range(10))
>>> a
array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
>>> a[3:]
array([3, 4, 5, 6, 7, 8, 9])

Combine this with a correct stride, you can probably get it to work.