red - How to use a struct passed by value in Red/System from a DLL

Question

I have some c code that looks like this:

extern "C" __declspec(dllexport) inline sfVector2f __cdecl sf_vector_create(
    float x, float y
) {
    std::cout << "x: " << x << " y: " << y << std::endl;
    sfVector2f vec = {x,y};  // just a struct of two floats
    return vec;
}

extern "C" __declspec(dllexport) inline void __cdecl test(
    sfSprite* sprite, sfVector2f wtf
) {
    std::cout << wtf.x << " " << wtf.y << std::endl;
    sfSprite_setPosition(sprite, wtf);
}

I invoke it from reds like this:

vec: sf-vector-create as float32! 100.0 as float32! 100.0 test mario-sprite vec

When I invoke this in reds, I get garbled results... why?

Answer 1

The C code is returning the vec struct on stack instead of returning a struct pointer. So in R/S, I guess you get back only the first entry of the struct. R/S does not yet support passing structs by value. But you can retrieve the rest of the values by some clever use of system/stack/* accessors to get a pointer on the beginning of the struct. Something like this should work:

sf-vector-create as float32! 100.0 as float32! 100.0
p: as byte-ptr! system/stack/top
vec: as vector! p - size? vector!

(Answer from @DocKimbel)