main.rs

#![allow(non_snake_case)]
use windows::{core::*, Win32::Foundation::*};

#[interface("17f409a1-f79d-45f6-962d-9db106cb7727")]
unsafe trait ICompositor: IUnknown {
    unsafe fn CreateVisual(&self, value: u32, visual: *mut Option<IVisual>) -> HRESULT;
    unsafe fn RenderVisual(&self, visual: std::mem::ManuallyDrop<Option<IVisual>>) -> HRESULT;
}

#[interface("34e49797-1302-4ad6-8975-dd7c5b286e72")]
unsafe trait IVisual: IUnknown {
    unsafe fn GetValue(&self, value: *mut u32) -> HRESULT;
}

#[implement(ICompositor)]
struct Compositor;

impl ICompositor_Impl for Compositor {
    unsafe fn CreateVisual(&self, value: u32, result: *mut Option<IVisual>) -> HRESULT {
        *result = Some(Visual(value).into());
        S_OK
    }

    unsafe fn RenderVisual(&self, visual: std::mem::ManuallyDrop<Option<IVisual>>) -> HRESULT {
        if let Some(visual) = &*visual {
            let mut value = 0;
            _ = visual.GetValue(&mut value);
            println!("value: {}", value);
            S_OK
        } else {
            E_FAIL
        }
    }
}

#[implement(IVisual)]
struct Visual(u32);

impl IVisual_Impl for Visual {
    unsafe fn GetValue(&self, value: *mut u32) -> HRESULT {
        *value = self.0;
        S_OK
    }
}

fn main() -> Result<()> {
    unsafe {
        let compositor: ICompositor = Compositor.into();

        let mut visual = None;
        compositor.CreateVisual(123, &mut visual).ok()?;

        compositor
            .RenderVisual(std::mem::transmute_copy(&visual))
            .ok()?;

        Ok(())
    }
}