libcamera: pipeline_handler: add PipelineHandler class

Provide a PipelineHandler which represents a handler for one or more
media devices and provides one or more cameras.

Signed-off-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

src/libcamera/include/pipeline_handler.h

@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2018, Google Inc.
+ *
+ * pipeline_handler.h - Pipeline handler infrastructure
+ */
+#ifndef __LIBCAMERA_PIPELINE_HANDLER_H__
+#define __LIBCAMERA_PIPELINE_HANDLER_H__
+
+#include <map>
+#include <string>
+#include <vector>
+
+#include <libcamera/camera.h>
+
+namespace libcamera {
+
+class DeviceEnumerator;
+class PipelineHandlerFactory;
+
+class PipelineHandler
+{
+public:
+	virtual ~PipelineHandler() { };
+
+	virtual bool match(DeviceEnumerator *enumerator) = 0;
+
+	virtual unsigned int count() = 0;
+	virtual Camera *camera(unsigned int id) = 0;
+};
+
+class PipelineHandlerFactory
+{
+public:
+	virtual ~PipelineHandlerFactory() { };
+
+	virtual PipelineHandler *create() = 0;
+
+	static void registerType(const std::string &name, PipelineHandlerFactory *factory);
+	static PipelineHandler *create(const std::string &name, DeviceEnumerator *enumerator);
+	static std::vector<std::string> handlers();
+
+private:
+	static std::map<std::string, PipelineHandlerFactory *> &registry();
+};
+
+#define REGISTER_PIPELINE_HANDLER(handler) \
+	class handler##Factory : public PipelineHandlerFactory { \
+	public: \
+		handler##Factory() \
+		{ \
+			PipelineHandlerFactory::registerType(#handler, this); \
+		} \
+		virtual PipelineHandler *create() { \
+			return new handler(); \
+		} \
+	}; \
+	static handler##Factory global_##handler##Factory;
+
+} /* namespace libcamera */
+
+#endif /* __LIBCAMERA_PIPELINE_HANDLER_H__ */

src/libcamera/meson.build

@@ -3,11 +3,13 @@ libcamera_sources = files([
     'device_enumerator.cpp',
     'log.cpp',
     'main.cpp',
+    'pipeline_handler.cpp',
 ])
 
 libcamera_headers = files([
     'include/device_enumerator.h',
     'include/log.h',
+    'include/pipeline_handler.h',
     'include/utils.h',
 ])
 

src/libcamera/pipeline_handler.cpp

@@ -0,0 +1,142 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2018, Google Inc.
+ *
+ * pipeline_handler.cpp - Pipeline handler infrastructure
+ */
+
+#include "device_enumerator.h"
+#include "log.h"
+#include "pipeline_handler.h"
+
+/**
+ * \file pipeline_handler.h
+ * \brief Create pipelines and cameras from one or more media devices
+ *
+ * Each pipeline supported by libcamera needs to be backed by a pipeline
+ * handler implementation which describes the one or many media devices
+ * needed for a pipeline to function properly.
+ *
+ * The pipeline handler is responsible for providing a description of the
+ * media devices it requires to operate. Once all media devices can be
+ * provided the pipeline handler can acquire them and create camera
+ * devices that utilize the acquired media devices.
+ *
+ * To make it a bit less bit complicated to write pipe line handlers a
+ * macro REGISTER_PIPELINE_HANDLER() is provided which allows a pipeline
+ * handler implementation to register itself with the library with ease.
+ */
+
+namespace libcamera {
+
+/**
+ * \class PipelineHandler
+ * \brief Find a set of media devices and provide cameras
+ *
+ * The responsibility of a PipelineHandler is to describe all media
+ * devices it would need in order to provide cameras to the system.
+ */
+
+/**
+ * \class PipelineHandlerFactory
+ * \brief Keep a registry and create instances of available pipeline handlers
+ *
+ * The responsibility of the PipelineHandlerFactory is to keep a list
+ * of all pipelines in the system. Each pipeline handler should register
+ * it self with the factory using the REGISTER_PIPELINE_HANDLER() macro.
+ */
+
+/**
+ * \brief Add a pipeline handler to the global list
+ *
+ * \param[in] name Name of the pipeline handler to add
+ * \param[in] factory Factory to use to construct the pipeline
+ *
+ * The caller is responsible to guarantee the uniqueness of the pipeline name.
+ */
+void PipelineHandlerFactory::registerType(const std::string &name,
+					  PipelineHandlerFactory *factory)
+{
+	std::map<std::string, PipelineHandlerFactory *> &factories = registry();
+
+	if (factories.count(name)) {
+		LOG(Error) <<  "Registering '" << name << "' pipeline twice";
+		return;
+	}
+
+	factories[name] = factory;
+}
+
+/**
+ * \brief Create a new pipeline handler and try to match the media devices it requires
+ *
+ * \param[in] name Name of the pipeline handler to try
+ * \param[in] enumerator Device enumerator to search for a match for the handler
+ *
+ * Try to match the media devices pipeline \a name requires against the ones
+ * registered in \a enumerator.
+ *
+ * \return Pipeline handler if a match was found, nullptr otherwise
+ */
+PipelineHandler *PipelineHandlerFactory::create(const std::string &name,
+						DeviceEnumerator *enumerator)
+{
+	std::map<std::string, PipelineHandlerFactory *> &factories = registry();
+
+	auto it = factories.find(name);
+	if (it == factories.end()) {
+		LOG(Error) << "Trying to create non-existing pipeline handler "
+			   << name;
+		return nullptr;
+	}
+
+	PipelineHandler *pipe = it->second->create();
+
+	if (pipe->match(enumerator))
+		return pipe;
+
+	delete pipe;
+	return nullptr;
+}
+
+/**
+ * \brief List all names of piepline handlers from the global list
+ *
+ * \return List of registerd pipeline handler names
+ */
+std::vector<std::string> PipelineHandlerFactory::handlers()
+{
+	std::map<std::string, PipelineHandlerFactory *> &factories = registry();
+	std::vector<std::string> handlers;
+
+	for (auto const &handler : factories)
+		handlers.push_back(handler.first);
+
+	return handlers;
+}
+
+/**
+ * \brief Static global list of pipeline handlers
+ *
+ * The static factories map is defined inside the function to ensures it gets
+ * initialized on first use, without any dependency on link order.
+ *
+ * \return Global list of pipeline handlers
+ */
+std::map<std::string, PipelineHandlerFactory *> &PipelineHandlerFactory::registry()
+{
+	static std::map<std::string, PipelineHandlerFactory *> factories;
+	return factories;
+}
+
+/**
+ * \def REGISTER_PIPELINE_HANDLER
+ * \brief Register a pipeline handler with the global list
+ *
+ * \param[in] handler Class name of PipelineHandler derived class to register
+ *
+ * Register a specific pipeline handler with the global list and make it
+ * available to try and match devices.
+ */
+
+} /* namespace libcamera */