Re: Function set-gl-vertex-array in Guile-opengl

[Catonano]

Hi Luis,

I hadn't guile-opengl installed, so I downloaded, built it and installed it
uust to see if I could reproduce this error you are running into

Il giorno ven 25 gen 2019 alle ore 15:58 Luis Souto Graña <
address@hidden> ha scritto:

> Hello, I'm trying to use the function set-gl-vertex-array in Guile-opengl .
> It needs a bytevector as an argument. I wrote this doing a copy-paste from
> here: https://github.com/marcomaggi/vicare/blob/master/attic/lab/gears.scm
>
> (use-modules (rnrs bytevectors))
> (use-modules (system foreign))
>
> (define (f32vector . lst)
>   (define-syntax f32set!
>     (syntax-rules ()
>       ((_ bv n value)
>        (bytevector-ieee-single-native-set! bv (* n 30) value))))
>   (let ((bv (make-bytevector (* (length lst) 30))))
>     (let loop ((i 0) (lst lst))
>       (cond ((null? lst) bv)
>         (else
>          (f32set! bv i (car lst))
>          (loop (+ i 1) (cdr lst)))))))
>


In my test I used the f32vector that comes with guile, I don't know how
it's different from the one you are defining here



>
> (define points (f32vector 30.0 30.0 0.0
>                       10.0 10.0 0.0
>                       70.0 30.0 0.0
>                       90.0 10.0 0.0
>                       70.0 70.0 0.0
>                       90.0 90.0 0.0
>                       30.0 70.0 0.0
>                       10.0 90.0 0.0
>                       30.0 30.0 0.0
>                       10.0 10.0 0.0))
>

Ok



> > points
> #vu8(0 0 240 65 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 240
>


in my case it's

scheme@(guile-user)> points
$1 = #f32(30.0 30.0 0.0 10.0 10.0 0.0 70.0 30.0 0.0 90.0 10.0 0.0 70.0 70.0
0.0 90.0 90.0 0.0 30.0 70.0 0.0 10.0 90.0 0.0 30.0 30.0 0.0 10.0 10.0 0.0)

I guess the difference is due to the fact that I used the one provided by
Guile

.....
>
> > (bytevector-length points)
> 900
>


In my case:

scheme@(guile-user)> (bytevector-length points)
$2 = 120



> > (bytevector->pointer points)
> #<pointer 0x56090d909aa0>
>


scheme@(guile-user)> (bytevector->pointer points)
$3 = #<pointer 0x5578953d25c0>


>
>
> So, it works well.
>
> Now, if I write:
>
> (use-modules (gl) (glut))
>
> > ,apropos set-gl-vertex-array
> (gl): set-gl-vertex-array    #<procedure set-gl-vertex-array (type
> bv-or-pointer #:optional size #:key stride offset)>
>
>
> > (set-gl-vertex-array (bytevector->pointer points) 3)
>
> ERROR: In procedure scm-error:
> unhandled array-pointer type 3
>



The first remark: the documentation you get with ,apropos reports:

(gl): set-gl-vertex-array    #<procedure set-gl-vertex-array (type
bv-or-pointer #:optional size #:key stride offset)>

The function requires the first argument to be a "type" and the second
argument to be a pointer to a bytevector

Now in your call to the function, the first argument you are passing is not
a type, it's a pointer to a bytevector

And the second argument is an integer number (3)

I don't now if the convention to express the types this function expects is
to use numbers (like in enumerations), it might be

But the way you're calling it seems incorrect

If you try to call it with a type first and then a pointer to a bytevector,
you might get a more interesting result

In my case what I found out is that the linking to opengl is broken

scheme@(guile-user)> (set-gl-vertex-array 3 (bytevector->pointer points) )
ERROR: In procedure dynamic-link:
In procedure dynamic-link: file: "libglut", message: "file not found"

Entering a new prompt.  Type `,bt' for a backtrace or `,q' to continue.
scheme@(guile-user) [1]>


So the libglut file can't be found

The libglut file should have been identified during the configuration phase
when I built guile-opengl

But it hasn't, it seems

I took a quick look at the guile-opengl configure.ac file and there's no
attempt at finding libglut

Also, the compiled files get installed in
$(libdir)/guile/$(GUILE_EFFECTIVE_VERSION)/ccache

all the other guile packages I have are installed in site-ccache, not in
ccache

So when I ,use the glut related namespaces in the REPL they get compiled
right there and then

I wondered if the unreachable ones in ccache are able to find libglut,
maybe because of some automagic mechanism I don't know about

I tried to fix the position for compiled files in the Automake.am file but
the problem persists

So this seems to be a lacking in the guile-opengl package

In fact, I see that the only contributor to guile-opengl is Andy Wingo

And putting the compiled files in ccache instead of site-ccache was a thing
in guile-fibers too

All other guile packages I have, put compiled files in site-ccache, I don't
know why Andy has this habit and other packages have a different habit
¯\_(ツ)_/¯

Often package authors can't deal with the Autotools, it seems to be too
hard not only for me. But I doubt Andy has this kind of difficutly, I
wonder why this is

That said, being on Ubuntu 18.04.1 what should I install in order to have
libglut on my system ?
I see a libgle3 that seems a good candidate. Is that the right one ?

If I had it I could try to sift through the internet myself and see if I
can improve the Autotools setup of guile-opengl

>From there on, you could explore the code more freely.

OR you could already have a better installation than I have, I don't know
¯\_(ツ)_/¯