Instruction file imported from quinnjr/skia-rs (.cursor/rules/ffi.mdc). Copyright stays with the author.

FFI Guidelines

C API Design

• All FFI functions in skia-rs-ffi
• Use opaque pointers for complex types
• Follow Skia's C API naming: sk_{type}_{method}
• Always check for null pointers

// skia-rs-ffi/src/lib.rs

/// Create a new paint object.
///
/// # Safety
/// Returns a valid pointer that must be freed with `sk_paint_delete`.
#[no_mangle]
pub unsafe extern "C" fn sk_paint_new() -> *mut Paint {
    Box::into_raw(Box::new(Paint::new()))
}

/// Delete a paint object.
///
/// # Safety
/// `paint` must be a valid pointer returned by `sk_paint_new`.
#[no_mangle]
pub unsafe extern "C" fn sk_paint_delete(paint: *mut Paint) {
    if !paint.is_null() {
        drop(Box::from_raw(paint));
    }
}

/// Set the paint color.
///
/// # Safety
/// `paint` must be a valid pointer.
#[no_mangle]
pub unsafe extern "C" fn sk_paint_set_color(paint: *mut Paint, color: u32) {
    if let Some(p) = paint.as_mut() {
        p.set_color32(Color(color));
    }
}

Type Mappings

Safety Requirements

• All FFI functions must be marked unsafe
• Document safety requirements in doc comments
• Check for null pointers before dereferencing
• Use #[repr(C)] for all FFI-visible structs