Is it possible to create a wasm file for an application that uses the C FFI?

[davidbruce]

@brendanfh Perhaps I missed it somewhere in the documentation, but is there a way to build a wasi file that has access to the C FFI?
I have the following Raylib bunnymark application:

#load "./lib/packages"

use core {*}
use raylib

MAX_BUNNIES := 50000

Bunny :: struct {
    position: raylib.Vector2; 
    speed: raylib.Vector2;
    color: raylib.Color
}

main :: () {
    raylib.InitWindow(800, 450, "Simple RAYLIB Window!");

    raylib.SetTargetFPS(144);

    texBunny: raylib.Texture2D;
    raylib.LoadTexture("resources/wabbit_alpha.png", &texBunny);
    texWidth := cast(f32) texBunny.width 
    texHeight := cast(f32) texBunny.height
    
    bunnies: [MAX_BUNNIES] Bunny;
    bunniesCount: i32 = 0;

    while (!raylib.WindowShouldClose()) {
        //if raylib.IsKeyPressed(.Q) {
        //     break;
        //}

        if raylib.IsMouseButtonDown(raylib.MouseButton.LEFT) {
            for i in 0 .. 100 {
                if bunniesCount < MAX_BUNNIES {
                    position: raylib.Vector2;
                    raylib.GetMousePosition(&position);
                    bunnies[bunniesCount] = Bunny.{
                        position = position,
                        speed = raylib.Vector2.{ 
                            x = random.float(-250.0, 250.0)/60,
                            y = random.float(-250.0, 250.0)/60 
                        },
                        color = raylib.Color.{
                            r = cast(u8) random.between(50, 240)
                            g = cast(u8) random.between(80, 240)
                            b = cast(u8) random.between(100, 240)
                            a = 255
                        }
                    }
                    bunniesCount = bunniesCount + 1
                }
            }
        }
        for i in 0 .. bunniesCount {
            bunnies[i].position.x = bunnies[i].position.x + bunnies[i].speed.x 
            bunnies[i].position.y = bunnies[i].position.y + bunnies[i].speed.y 
            if (bunnies[i].position.x + texWidth/2 > 800 || bunnies[i].position.x + texWidth/2 < 0) {
                bunnies[i].speed.x *= -1
            }
            if (bunnies[i].position.y + texWidth/2 > 450 || bunnies[i].position.y + texWidth/2 < 0) {
                bunnies[i].speed.y *= -1
            }
            
        }
        // pos := raylib.GetMousePosition();
        bunnyCountText := tprintf("{}\0", bunniesCount);
        
        raylib.BeginDrawing();
        raylib.ClearBackground(raylib.RAYWHITE);
        for i in 0 .. bunniesCount {
            raylib.DrawTexture(
                texBunny,
                cast(i32) bunnies[i].position.x,
                cast(i32) bunnies[i].position.y,
                bunnies[i].color
            );
        }
        raylib.DrawRectangleRec(raylib.Rectangle.{0, 0, cast(f32) raylib.GetScreenWidth(), 40}, raylib.BLACK);
        raylib.DrawText(bunnyCountText.data, 120, 10, 20, raylib.GREEN);
        raylib.DrawFPS(10, 10);
        raylib.EndDrawing();
    }

    raylib.CloseWindow();
}

I can compile without errors doing the following:

onyx build -r wasi -o bunnymark.wasm bunnymark.onyx ~/.onyx/core/runtime/default_link_options.onyx ~/.onyx/core/onyx/cbindgen.onyx ~/.onyx/core/onyx/compiler_extension.onyx ~/.onyx/core/onyx/cptr.onyx ~/.onyx/core/onyx/fault_handling.onyx

However, when I attempt to run with wasmer:

error: Instantiation failed
╰─▶ 1: Error while importing "onyx_raylib"."GetMonitorPosition": unknown import. Expected Function(FunctionType { params: [I32, I32], results: [] })

I assume this isn't really possible since onyx embeds wasmer and is doing some kind of magic to make it link properly to a dynamic lib?

[brendanfh]

Yes, you are correct. When you run a program with onyx run ... it has extra logic to resolve the native C-FFI functions. This is a rather non-standard feature in the WASM world and it violates some of the isolation/security principles that WASM generally has, so I wouldn't expect any other runtimes to support anything like this. It only exists for Onyx to allow for support of more "useful" native things like Raylib/OpenGL/etc.

If you're curious about the implementation you can see some of the important functions here.
wasm_runtime.c#150
wasm_runtime.c#447

[davidbruce]

Thank you for the info and the links to the code!

It's a pretty clever feature and the overhead of calling C doesn't seem that high. With raylib bunnymark I was able to hit around 100fps. Changing to a SoA data structure didn't seem to change the outcome leading me to believe the performance loss is the draw calls. I figured using LLVM as the wasmer compiler would yield higher performance, but I couldn't get a build working without it segfaulting. I didn't spend too much time trying, I just slapped wasm_config_set_compiler into wasm_runtime.c after the feature flags are set.

Regardless that's not bad at all, considering a debug build of Nim is hitting 85-90fps and 120-130 with a release build.

I'm not sure if I'll truly use Onyx, but this FFI feature has me very intrigued about the possibilities of WASM on desktop. Also, coming from F# I certainly love the pipe operator!