Merge pull request mozilla#258 from ChunMinChang/avif-alpha-capi

Add an API exposing alpha_item and premultiplied_alpha

Author: baumanj

mp4parse_capi/fuzz/fuzz_targets/avif.rs

@@ -29,8 +29,8 @@ fuzz_target!(|data: &[u8]| {
             return;
         }
 
-        let mut primary_item = Default::default();
-        mp4parse_avif_get_primary_item(context, &mut primary_item);
+        let mut avif_image = Default::default();
+        mp4parse_avif_get_image(context, &mut avif_image);
 
         mp4parse_avif_free(context);
     }

mp4parse_capi/src/lib.rs

@@ -436,6 +436,14 @@ pub struct Mp4parseParser {
     video_track_sample_descriptions: TryHashMap<u32, TryVec<Mp4parseTrackVideoSampleInfo>>,
 }
 
+#[repr(C)]
+#[derive(Default)]
+pub struct AvifImage {
+    pub primary_item: Mp4parseByteData,
+    pub alpha_item: Mp4parseByteData,
+    pub premultiplied_alpha: bool,
+}
+
 /// A unified interface for the parsers which have different contexts, but
 /// share the same pattern of construction. This allows unification of
 /// argument validation from C and minimizes the surface of unsafe code.
@@ -1177,26 +1185,31 @@ fn mp4parse_get_track_video_info_safe(
 /// # Safety
 ///
 /// This function is unsafe because it dereferences both the parser and
-/// primary_item raw pointers passed into it. Callers should ensure the parser
-/// pointer points to a valid `Mp4parseAvifParser`, and that the primary_item
-/// pointer points to a valid `Mp4parseByteData`. If there was not a previous
+/// avif_image raw pointers passed into it. Callers should ensure the parser
+/// pointer points to a valid `Mp4parseAvifParser`, and that the avif_image
+/// pointer points to a valid `AvifImage`. If there was not a previous
 /// successful call to `mp4parse_avif_read()`, no guarantees are made as to
-/// the state of `primary_item`.
+/// the state of `avif_image`. If `avif_image.alpha_item` is set to a
+/// positive `length` and non-null `data`, then the `avif_image` contains an
+/// valid alpha channel data. Otherwise, the image is opaque.
 #[no_mangle]
-pub unsafe extern "C" fn mp4parse_avif_get_primary_item(
+pub unsafe extern "C" fn mp4parse_avif_get_image(
     parser: *mut Mp4parseAvifParser,
-    primary_item: *mut Mp4parseByteData,
+    avif_image: *mut AvifImage,
 ) -> Mp4parseStatus {
-    if parser.is_null() {
+    if parser.is_null() || avif_image.is_null() {
         return Mp4parseStatus::BadArg;
     }
 
     // Initialize fields to default values to ensure all fields are always valid.
-    *primary_item = Default::default();
-
+    *avif_image = Default::default();
     let context = (*parser).context();
 
-    (*primary_item).set_data(context.primary_item());
+    (*avif_image).primary_item.set_data(context.primary_item());
+    if let Some(context_alpha_item) = context.alpha_item() {
+        (*avif_image).alpha_item.set_data(context_alpha_item);
+        (*avif_image).premultiplied_alpha = context.premultiplied_alpha;
+    }
 
     Mp4parseStatus::Ok
 }