PyGLM types do not support PyBUF_SIMPLE

[einarf]

Example from mat_getbuffer

if ((flags & PyBUF_RECORDS_RO) != PyBUF_RECORDS_RO || (flags & PyBUF_F_CONTIGUOUS) == PyBUF_F_CONTIGUOUS || (flags & PyBUF_ANY_CONTIGUOUS) == PyBUF_ANY_CONTIGUOUS) {
	PyErr_SetString(PyExc_BufferError, "This type of buffer is not supported.");
	view->obj = NULL;
	return -1;
}

Most types (if not all) do pass the PyBuffer_IsContiguous() tests, so I assume all types have contiguous buffer data. Still, the various *_getbuffer methods do not accept this flag.

We discovered this issue when trying to set uniform or buffer data in moderngl.

program['uniform'].value = (1, 1, 1)    # working
program['uniform'].write(np.array([1,1,1]))    # working

v = glm.fvec3(1,1,1)
program['uniform'].write(memoryview(v))    # working
program['uniform'].write(bytes(v))    # working
program['uniform'].write(np.array(v))    # working

program['uniform'].write(v)    #  <--------- error

Error output:

BufferError: This type of buffer is not supported.

We obtain the buffer using:

PyObject_GetBuffer(value, &buffer_view, PyBUF_SIMPLE);

This is acceptable when you just want to write contiguous to an opengl buffer and have no plans to keep the buffer reference or modify it.

More details here:
moderngl/moderngl#379

[Zuzu-Typ]

I'm not sure I understand what you're getting at.

Most types (if not all) do pass the PyBuffer_IsContiguous() tests, so I assume all types have contiguous buffer data. Still, the various *_getbuffer methods do not accept this flag.

PyBUF_SIMPLE has nothing to do with contiguity. It's about the structure of the data (see here).

It doesn't make sense to me for PyGLM to provide buffers with less complexity than PyBUF_STRIDES.
The buffers it provides needs to provide information about the shape (e.g. (4, 4) for mat4x4) and stride (e.g. sizeof(double) for dmat4x4). Otherwise the buffer data would be useless (unless the calling function knew the shape anyway).

PyGLM accepts any buffer requests that have at least the PyBUF_RECORDS_RO flag and not fortan contiguity (because the data is layed out in C contiguity).

[Zuzu-Typ]

I guess I could add support for less complex buffer structures in case a program wants that.

[einarf]

Sorry, I was rambling a bit trying to figure things out while learning in the process 😄

Yes it would definitely be nice to have support for less complex buffer structures so they can be used just like memoryview, bytes and np arrays. Could of course just wrap them in a memoryview or something, but that does seem unnecessary.

[einarf]

Works now. Thank you.

[aforren1]

It looks like a6c0f1f introduced a strides check, so PyBUF_SIMPLE requests don't seem to work from v2.0.0a3 onward. Any chance that check can be removed so PyBUF_SIMPLE works again, or am I missing some other detail? Thanks!

[Zuzu-Typ]

It looks like a6c0f1f introduced a strides check, so PyBUF_SIMPLE requests don't seem to work from v2.0.0a3 onward. Any chance that check can be removed so PyBUF_SIMPLE works again, or am I missing some other detail? Thanks!

I don't know why exactly I added that check back in.
I'll fix it right away.
Thanks for letting me know (:

[aforren1]

Great, thanks for the fix!

[einarf]

Thanks! I just noticed this late last night when upgrading pyglm. Writing uniform data to shaders did not work any more in moderngl and arcade using the buffer protocol.