gstreamer: Add bindings to MiniObject together with casting functionality

This is only possible with 1.20 because gst_mini_object_get_type() was
added then. Previous versions only provide bindings for the specific
types, like Caps, Event, etc.

Fixes https://gitlab.freedesktop.org/gstreamer/gstreamer-rs/-/issues/353

gstreamer/src/lib.rs

@@ -45,6 +45,7 @@ pub use crate::error::*;
 
 #[macro_use]
 pub mod miniobject;
+pub use miniobject::{MiniObject, MiniObjectRef};
 pub mod message;
 pub use crate::message::{Message, MessageErrorDomain, MessageRef, MessageView};
 
@@ -310,6 +311,8 @@ pub mod prelude {
     pub use crate::typefind::TypeFindImpl;
     pub use crate::value::GstValueExt;
 
+    pub use crate::miniobject::IsMiniObject;
+
     pub use crate::tags::{CustomTag, Tag};
 
     pub use muldiv::MulDiv;

gstreamer/src/miniobject.rs

@@ -1,5 +1,14 @@
 // Take a look at the license at the top of the repository in the LICENSE file.
 
+use glib::translate::*;
+
+pub trait IsMiniObject:
+    AsRef<Self::RefType> + FromGlibPtrFull<*mut Self::FfiType> + Send + Sync + 'static
+{
+    type RefType;
+    type FfiType;
+}
+
 #[macro_export]
 macro_rules! mini_object_wrapper (
     ($name:ident, $ref_name:ident, $ffi_name:path) => {
@@ -10,6 +19,11 @@ macro_rules! mini_object_wrapper (
         #[repr(transparent)]
         pub struct $ref_name($ffi_name);
 
+        impl $crate::miniobject::IsMiniObject for $name {
+            type RefType = $ref_name;
+            type FfiType = $ffi_name;
+        }
+
         impl $name {
             pub unsafe fn from_glib_none(ptr: *const $ffi_name) -> Self {
                 skip_assert_initialized!();
@@ -78,6 +92,12 @@ macro_rules! mini_object_wrapper (
                 }
             }
 
+            pub fn upcast(self) -> $crate::miniobject::MiniObject {
+                unsafe {
+                    from_glib_full(self.into_ptr() as *mut $crate::ffi::GstMiniObject)
+                }
+            }
+
             pub unsafe fn into_ptr(self) -> *mut $ffi_name {
                 let s = std::mem::ManuallyDrop::new(self);
                 s.as_mut_ptr()
@@ -392,6 +412,18 @@ macro_rules! mini_object_wrapper (
                     ) as *const $ffi_name)
                 }
             }
+
+            pub fn upcast_ref(&self) -> &$crate::miniobject::MiniObjectRef {
+                unsafe {
+                    &*(self.as_ptr() as *const $crate::miniobject::MiniObjectRef)
+                }
+            }
+
+            pub fn upcast_mut(&mut self) -> &mut $crate::miniobject::MiniObjectRef {
+                unsafe {
+                    &mut *(self.as_mut_ptr() as *mut $crate::miniobject::MiniObjectRef)
+                }
+            }
         }
 
         impl $crate::glib::translate::GlibPtrDefault for $ref_name {
@@ -485,3 +517,43 @@ macro_rules! mini_object_wrapper (
         // immutable references from a mutable reference without borrowing via the value
     };
 );
+
+#[cfg(not(any(feature = "v1_20", feature = "dox")))]
+mini_object_wrapper!(MiniObject, MiniObjectRef, ffi::GstMiniObject);
+
+#[cfg(any(feature = "v1_20", feature = "dox"))]
+mini_object_wrapper!(MiniObject, MiniObjectRef, ffi::GstMiniObject, || {
+    ffi::gst_mini_object_get_type()
+});
+
+impl MiniObject {
+    pub fn downcast<T: IsMiniObject + glib::StaticType>(self) -> Result<T, Self> {
+        if self.type_().is_a(T::static_type()) {
+            unsafe { Ok(from_glib_full(self.into_ptr() as *mut T::FfiType)) }
+        } else {
+            Err(self)
+        }
+    }
+}
+
+impl MiniObjectRef {
+    pub fn type_(&self) -> glib::Type {
+        unsafe { from_glib((*self.as_ptr()).type_) }
+    }
+
+    pub fn downcast_ref<T: IsMiniObject + glib::StaticType>(&self) -> Option<&T> {
+        if self.type_().is_a(T::static_type()) {
+            unsafe { Some(&*(self as *const Self as *const T)) }
+        } else {
+            None
+        }
+    }
+
+    pub fn downcast_mut<T: IsMiniObject + glib::StaticType>(&mut self) -> Option<&mut T> {
+        if self.type_().is_a(T::static_type()) {
+            unsafe { Some(&mut *(self as *mut Self as *mut T)) }
+        } else {
+            None
+        }
+    }
+}

gstreamer/src/subclass/tracer.rs

@@ -2,8 +2,8 @@
 
 use crate::ffi;
 use crate::{
-    Bin, Buffer, BufferList, Element, Event, FlowReturn, Message, Object, Pad, PadLinkReturn,
-    Query, StateChange, StateChangeReturn, Tracer,
+    Bin, Buffer, BufferList, Element, Event, FlowReturn, Message, MiniObject, Object, Pad,
+    PadLinkReturn, Query, StateChange, StateChangeReturn, Tracer,
 };
 use glib::{prelude::*, subclass::prelude::*, translate::*};
 
@@ -29,6 +29,14 @@ pub trait TracerImpl: TracerImplExt + ObjectImpl + Send + Sync {
     fn element_query_post(&self, ts: u64, element: &Element, query: &Query, success: bool) {}
     fn element_query_pre(&self, ts: u64, element: &Element, query: &Query) {}
     fn element_remove_pad(&self, ts: u64, element: &Element, pad: &Pad) {}
+    // rustdoc-stripper-ignore-next
+    /// Hook to be called before the GstMiniObject has been fully initialized.
+    fn mini_object_created(&self, ts: u64, object: std::ptr::NonNull<ffi::GstMiniObject>) {}
+    // rustdoc-stripper-ignore-next
+    /// Hook to be called after the GstMiniObject has been finalized.
+    fn mini_object_destroyed(&self, ts: u64, object: std::ptr::NonNull<ffi::GstMiniObject>) {}
+    fn mini_object_reffed(&self, ts: u64, object: &MiniObject, new_refcount: i32) {}
+    fn mini_object_unreffed(&self, ts: u64, object: &MiniObject, new_refcount: i32) {}
     fn object_created(&self, ts: u64, object: &Object) {}
     // rustdoc-stripper-ignore-next
     /// Hook to be called after the GstObject has been finalized.
@@ -169,11 +177,22 @@ define_tracer_hooks! {
         let p = Pad::from_glib_borrow(p);
         this.element_remove_pad(ts, &e, &p)
     };
-    // TODO(#353): Missing bindings to `GstMiniObject`.
-    // MiniObjectCreated,
-    // MiniObjectDestroyed,
-    // MiniObjectReffed,
-    // MiniObjectUnreffed,
+    // TODO: unclear what to do here as the `GstMiniObject` here is not fully initialized yet…
+    MiniObjectCreated("mini-object-created") = |this, ts, o: *mut ffi::GstMiniObject| {
+        this.mini_object_created(ts, std::ptr::NonNull::new_unchecked(o))
+    };
+    // TODO: unclear what to do here as the `GstMiniObject` here is no longer valid…
+    MiniObjectDestroyed("mini-object-destroyed") = |this, ts, o: *mut ffi::GstMiniObject| {
+        this.mini_object_destroyed(ts, std::ptr::NonNull::new_unchecked(o))
+    };
+    MiniObjectReffed("mini-object-reffed") = |this, ts, o: *mut ffi::GstMiniObject, rc: libc::c_int| {
+        let o = MiniObject::from_glib_borrow(o);
+        this.mini_object_reffed(ts, &o, rc as i32)
+    };
+    MiniObjectUnreffed("mini-object-unreffed") = |this, ts, o: *mut ffi::GstMiniObject, rc: libc::c_int| {
+        let o = MiniObject::from_glib_borrow(o);
+        this.mini_object_unreffed(ts, &o, rc as i32)
+    };
     ObjectCreated("object-created") = |this, ts, o: *mut ffi::GstObject| {
         let o = Object::from_glib_borrow(o);
         this.object_created(ts, &o)

gstreamer/sys/Gir.toml

@@ -169,6 +169,13 @@ status = "generate"
     name = "steal"
     version = "1.18.3"
 
+[[object]]
+name = "Gst.MiniObject"
+status = "generate"
+    [[object.function]]
+    name = "get_type"
+    version = "1.20"
+
 [[object]]
 name = "Gst.Memory"
 status = "generate"

gstreamer/sys/src/lib.rs

@@ -5728,6 +5728,8 @@ extern "C" {
     //=========================================================================
     // GstMiniObject
     //=========================================================================
+    #[cfg(any(feature = "v1_20", feature = "dox"))]
+    #[cfg_attr(feature = "dox", doc(cfg(feature = "v1_20")))]
     pub fn gst_mini_object_get_type() -> GType;
     #[cfg(any(feature = "v1_16", feature = "dox"))]
     #[cfg_attr(feature = "dox", doc(cfg(feature = "v1_16")))]