On 07 Apr 2016, at 14:15, Damien Pollet <damien.pollet+pharo@gmail.com> wrote:

I think in that case you need to pass an instance of FFIExternalValueHolder.

yes.

you can take the test FFIExternalValueHolderTests>>testCall as an example.

But since it uses anonymous classes it might require a better explanation, there is the class comment, but basically, you do this:

1) Declare a class variable

MyClass class>>initialize

INT_PTR := FFIExternalValueHolder ofType: ��int��.

2) Replace "int *�� in your function calls with your new type:

glGetAttribute: attr into: value

^ self ffiCall: #( int SDL_GL_GetAttribute(SDL_GLattr attr, INT_PTR value) )

3) pass an instance of INT_PTR to get the value:

| ptr value |

ptr := INT_PTR new.

self glGetAttribute: anAttributeIDontKnow into: ptr.

value := ptr value.

Esteban

On 7 April 2016 at 17:42, Thibault Raffaillac <thibault.raffaillac@inria.fr> wrote:
Hi again,

Does anyone know what is the state of return by reference in FFI?
Example:
glGetAttribute: attr into: value
<primitive: #primitiveNativeCall module: #NativeBoostPlugin error: errorCode>
^ self nbCall: #( int SDL_GL_GetAttribute(SDL_GLattr attr, int *value) )

On my image (50666) it does nothing on value yet (if nil, remains nil, if SmallInteger 0, remains 0).
(SDL2 glGetAttribute: 6 into: value) should return 16.
I've seen NBOpenGL put "out" before value in method header, should it matter? (does not make it work though)
Last but not least, should we attach '*' to the type or variable for FFI to understand it is a pointer?

Cheers,
Thibault Raffaillac