libcamera: base: signal: Support connecting signals to functors

It can be useful to connect a signal to a functor, and in particular a
lambda function, while still operating in the context of a receiver
object (to support both object-based disconnection and queued
connections to Object instances).

Add a BoundMethodFunctor class to bind a functor, and a corresponding
Signal::connect() function. There is no corresponding disconnect()
function, as a lambda passed to connect() can't be later passed to
disconnect(). Disconnection typically uses disconnect(T *object), which
will cover the vast majority of use cases.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>

2 files changed, 50 insertions, 0 deletions

diff --git a/include/libcamera/base/bound_method.h b/include/libcamera/base/bound_method.h
index 76ce8017..ebd297ab 100644
--- a/include/libcamera/base/bound_method.h
+++ b/include/libcamera/base/bound_method.h
@@ -128,6 +128,37 @@ public:
 	virtual R invoke(Args... args) = 0;
 };
 
+template<typename T, typename R, typename Func, typename... Args>
+class BoundMethodFunctor : public BoundMethodArgs<R, Args...>
+{
+public:
+	using PackType = typename BoundMethodArgs<R, Args...>::PackType;
+
+	BoundMethodFunctor(T *obj, Object *object, Func func,
+			   ConnectionType type = ConnectionTypeAuto)
+		: BoundMethodArgs<R, Args...>(obj, object, type), func_(func)
+	{
+	}
+
+	R activate(Args... args, bool deleteMethod = false) override
+	{
+		if (!this->object_)
+			return func_(args...);
+
+		auto pack = std::make_shared<PackType>(args...);
+		bool sync = BoundMethodBase::activatePack(pack, deleteMethod);
+		return sync ? pack->returnValue() : R();
+	}
+
+	R invoke(Args... args) override
+	{
+		return func_(args...);
+	}
+
+private:
+	Func func_;
+};
+
 template<typename T, typename R, typename... Args>
 class BoundMethodMember : public BoundMethodArgs<R, Args...>
 {
diff --git a/include/libcamera/base/signal.h b/include/libcamera/base/signal.h
index c2521769..8d9f82f6 100644
--- a/include/libcamera/base/signal.h
+++ b/include/libcamera/base/signal.h
@@ -61,6 +61,25 @@ public:
 		SignalBase::connect(new BoundMethodMember<T, R, Args...>(obj, nullptr, func));
 	}
 
+#ifndef __DOXYGEN__
+	template<typename T, typename Func,
+		 typename std::enable_if_t<std::is_base_of<Object, T>::value> * = nullptr>
+	void connect(T *obj, Func func, ConnectionType type = ConnectionTypeAuto)
+	{
+		Object *object = static_cast<Object *>(obj);
+		SignalBase::connect(new BoundMethodFunctor<T, void, Func, Args...>(obj, object, func, type));
+	}
+
+	template<typename T, typename Func,
+		 typename std::enable_if_t<!std::is_base_of<Object, T>::value> * = nullptr>
+#else
+	template<typename T, typename Func>
+#endif
+	void connect(T *obj, Func func)
+	{
+		SignalBase::connect(new BoundMethodFunctor<T, void, Func, Args...>(obj, nullptr, func));
+	}
+
 	template<typename R>
 	void connect(R (*func)(Args...))
 	{