Re: Custom foreign types

On 6/16/24 7:13 PM, Ryan Raymond wrote:
> Hello, all.
> I know we can create pointers to structs with make-c-struct, but I would
> like to pass structs directly as arguments to foreign functions. I can do
> that by using bytevector-uint-ref, and setting the size to that of the
> struct, but when it is time to specify the type in pointer->procedure, I am
> out of luck if the sizes don't match.
>
> Here is how I am binding Raylib using FFI currently.
>
> (use-modules
>    (rnrs bytevectors)
>    (system foreign))
> (define rl (dynamic-link "libraylib"))
> (define pp pointer->procedure)
> (define df dynamic-func)
>
> (define BeginDrawing (pp void (df "BeginDrawing" rl) '()))
> (define ClearBackground_c (pp void (df "ClearBackground" rl) (list uint32)))
> (define (ClearBackground color)
>    (ClearBackground_c (make-c-struct (list uint8 uint8 uint8 uint8) color)))
> (define CloseWindow (pp void (df "CloseWindow" rl) '()))
> (define DrawGrid (pp void (df "DrawPlane" rl) (list int float)))
> (define EndDrawing (pp void (df "EndDrawing" rl) '()))
> (define GetFrameTime (pp float (df "GetFrameTime" rl) '()))
> (define InitWindow_c (pp void (df "InitWindow" rl) (list int int '*)))
> (define (InitWindow width height title) (InitWindow_c width height
> (string->pointer title)))
> (define SetTargetFPS (pp void (df "SetTargetFPS" rl) (list int)))
> (define WindowShouldClose_c (pp int8 (df "WindowShouldClose" rl) '()))
> (define (WindowShouldClose) (= 1 (WindowShouldClose_c)))
>
> (define width 600)
> (define height 400)
> (define title "This is a Guile-bound thinga")
>
> (define (make-Color r g b a)
>    (bytevector-uint-ref
>      (u8-list->bytevector (list r g b a)) 0 (native-endianness) 4))
>
> (define (make-Vector3 x y z)
>    (bytevector-uint-ref
>      (f32vector x y z) 0 (native-endianness) 4))
>
>
> Is there a cleaner way to do this?
> Ryan

Since Color is a struct of four chars you need to declare ClearBackground as
  (pp void (df "ClearBackground" rl)  (list (list char char char char)))

Matt