Cursor rule

1---
2description: FFI (Foreign Function Interface) guidelines for skia-rs-ffi
3globs: ["crates/skia-rs-ffi/**"]
4alwaysApply: false
5---
6 
7# FFI Guidelines
8 
9## C API Design
10 
11- All FFI functions in `skia-rs-ffi`
12- Use opaque pointers for complex types
13- Follow Skia's C API naming: `sk_{type}_{method}`
14- Always check for null pointers
15 
16```rust
17// skia-rs-ffi/src/lib.rs
18 
19/// Create a new paint object.
20///
21/// # Safety
22/// Returns a valid pointer that must be freed with `sk_paint_delete`.
23#[no_mangle]
24pub unsafe extern "C" fn sk_paint_new() -> *mut Paint {
25    Box::into_raw(Box::new(Paint::new()))
26}
27 
28/// Delete a paint object.
29///
30/// # Safety
31/// `paint` must be a valid pointer returned by `sk_paint_new`.
32#[no_mangle]
33pub unsafe extern "C" fn sk_paint_delete(paint: *mut Paint) {
34    if !paint.is_null() {
35        drop(Box::from_raw(paint));
36    }
37}
38 
39/// Set the paint color.
40///
41/// # Safety
42/// `paint` must be a valid pointer.
43#[no_mangle]
44pub unsafe extern "C" fn sk_paint_set_color(paint: *mut Paint, color: u32) {
45    if let Some(p) = paint.as_mut() {
46        p.set_color32(Color(color));
47    }
48}
49```
50 
51## Type Mappings
52 
53| Skia C++ | Rust | C FFI |
54|----------|------|-------|
55| `SkScalar` | `Scalar` (f32) | `float` |
56| `SkPoint` | `Point` | `sk_point_t` |
57| `SkRect` | `Rect` | `sk_rect_t` |
58| `SkColor` | `Color` | `uint32_t` |
59| `SkMatrix` | `Matrix` | `sk_matrix_t` |
60| `SkPath*` | `*mut Path` | `sk_path_t*` |
61| `SkPaint*` | `*mut Paint` | `sk_paint_t*` |
62| `SkCanvas*` | `*mut Canvas` | `sk_canvas_t*` |
63 
64## Safety Requirements
65 
66- All FFI functions must be marked `unsafe`
67- Document safety requirements in doc comments
68- Check for null pointers before dereferencing
69- Use `#[repr(C)]` for all FFI-visible structs
70