On 08 Apr 2016, at 11:34, Esteban Lorenzano <estebanlm@gmail.com> wrote:

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

as a larger explanation, this will create an anonymous subclass to keep “int” values, than later you can use as a type in your function call. Some people would call this obscure, but is a good way of solving this problem (I adopted it from old NB). If you want to have a named class instead an anonymous class, you can just subclass FFIExternalValueHolder: FFIExternalValueHolder subclass: #MyIntPtr and then implement typeDecl class method MyIntPtr class>>typeDecl ^ ‘int' and this will work as the anonymous class

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

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On 7 April 2016 at 17:42, Thibault Raffaillac <thibault.raffaillac@inria.fr <mailto: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