From e21e0b80154afe4a62480efca61a07d4c2f2b0ef Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Mon, 3 Oct 2016 17:00:11 +0300
Subject: [PATCH] Add a system creation function with automatic backend
 detection

---
 source/openvr/openvrsystem.cpp |  5 +++++
 source/openvr/openvrsystem.h   |  2 ++
 source/system.cpp              | 26 ++++++++++++++++++++++++++
 source/system.h                |  1 +
 4 files changed, 34 insertions(+)

diff --git a/source/openvr/openvrsystem.cpp b/source/openvr/openvrsystem.cpp
index e71ba33..c137400 100644
--- a/source/openvr/openvrsystem.cpp
+++ b/source/openvr/openvrsystem.cpp
@@ -47,6 +47,11 @@ OpenVRSystem::~OpenVRSystem()
 		vr::VR_Shutdown();
 }
 
+bool OpenVRSystem::is_maybe_available()
+{
+	return vr::VR_IsHmdPresent();
+}
+
 void OpenVRSystem::configure_view(StereoView &view) const
 {
 	vr::IVRSystem *vr_sys = vr::VRSystem();
diff --git a/source/openvr/openvrsystem.h b/source/openvr/openvrsystem.h
index 3e401ed..4988659 100644
--- a/source/openvr/openvrsystem.h
+++ b/source/openvr/openvrsystem.h
@@ -20,6 +20,8 @@ public:
 	OpenVRSystem();
 	~OpenVRSystem();
 
+	static bool is_maybe_available();
+
 	virtual void configure_window(Graphics::Window &) const { }
 	virtual void configure_view(StereoView &) const;
 	virtual void set_absolute_tracking(bool);
diff --git a/source/system.cpp b/source/system.cpp
index 99a6d48..c835456 100644
--- a/source/system.cpp
+++ b/source/system.cpp
@@ -25,5 +25,31 @@ System *System::create(const string &type)
 	throw invalid_argument(format("system '%s' not supported", type));
 }
 
+System *System::create_autodetect()
+{
+#ifdef WITH_OPENVR
+	if(OpenVRSystem::is_maybe_available())
+	{
+		try
+		{
+			return new OpenVRSystem;
+		}
+		catch(const runtime_error &)
+		{ }
+	}
+#endif
+
+#ifdef WITH_LIBOVR
+	try
+	{
+		return new LibOVRSystem;
+	}
+	catch(const runtime_error &)
+	{ }
+#endif
+
+	return 0;
+}
+
 } // namespace VR
 } // namespace Msp
diff --git a/source/system.h b/source/system.h
index 46c65d9..f7e28b5 100644
--- a/source/system.h
+++ b/source/system.h
@@ -20,6 +20,7 @@ public:
 	virtual ~System() { }
 
 	static System *create(const std::string &);
+	static System *create_autodetect();
 
 	virtual void configure_window(Graphics::Window &) const = 0;
 	virtual void configure_view(StereoView &) const = 0;
-- 
2.45.2