description: FFI (Foreign Function Interface) guidelines for skia-rs-ffi globs: ["crates/skia-rs-ffi/**"] alwaysApply: false

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

| Skia C++ | Rust | C FFI | |----------|------|-------| | SkScalar | Scalar (f32) | float | | SkPoint | Point | sk_point_t | | SkRect | Rect | sk_rect_t | | SkColor | Color | uint32_t | | SkMatrix | Matrix | sk_matrix_t | | SkPath* | *mut Path | sk_path_t* | | SkPaint* | *mut Paint | sk_paint_t* | | SkCanvas* | *mut Canvas | sk_canvas_t* |

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