OpenVr: fix for conflict between openvr and oculus display plugins

* Call vr::VR_Shutdown() when ref-count goes to zero.  The ref-count
  is ncessary because the vr::IVRSystem poitner is shared between the
  the openvr input and display plugins.
* OpenVR plugins options will display in the menu if vr::VR_IsHmdPresent() is true.
  This is faster then initializing all of openvr and less likely to conflict with the
  oculus display plugin.

plugins/oculus/src/OculusBaseDisplayPlugin.cpp

@@ -39,6 +39,7 @@ glm::mat4 OculusBaseDisplayPlugin::getHeadPose(uint32_t frameIndex) const {
 
 bool OculusBaseDisplayPlugin::isSupported() const {
     if (!OVR_SUCCESS(ovr_Initialize(nullptr))) {
+        qDebug() << "OculusBaseDisplayPlugin : ovr_Initialize() failed";
         return false;
     }
 
@@ -48,6 +49,7 @@ bool OculusBaseDisplayPlugin::isSupported() const {
     if (!OVR_SUCCESS(result)) {
         ovrErrorInfo error;
         ovr_GetLastErrorInfo(&error);
+        qDebug() << "OculusBaseDisplayPlugin : ovr_Create() failed" << result << error.Result << error.ErrorString;
         ovr_Shutdown();
         return false;
     }

plugins/openvr/src/OpenVrDisplayPlugin.cpp

@@ -72,10 +72,7 @@ mat4 toGlm(const vr::HmdMatrix34_t& m) {
 }
 
 bool OpenVrDisplayPlugin::isSupported() const {
-    auto hmd = acquireOpenVrSystem();
+    return vr::VR_IsHmdPresent();
-    bool success = nullptr != hmd;
-    releaseOpenVrSystem();
-    return success;
 }
 
 void OpenVrDisplayPlugin::activate() {

plugins/openvr/src/OpenVrHelpers.cpp

@@ -23,11 +23,11 @@ using Lock = std::unique_lock<Mutex>;
 static int refCount { 0 };
 static Mutex mutex;
 static vr::IVRSystem* activeHmd { nullptr };
-static bool hmdPresent = vr::VR_IsHmdPresent();
 
 static const uint32_t RELEASE_OPENVR_HMD_DELAY_MS = 5000;
 
 vr::IVRSystem* acquireOpenVrSystem() {
+    bool hmdPresent = vr::VR_IsHmdPresent();
     if (hmdPresent) {
         Lock lock(mutex);
         if (!activeHmd) {
@@ -53,24 +53,7 @@ void releaseOpenVrSystem() {
         --refCount;
         if (0 == refCount) {
             qCDebug(displayplugins) << "openvr: zero refcount, deallocate VR system";
-            // Avoid spamming the VR system with activate/deactivate calls at system startup by
+            vr::VR_Shutdown();
-            // putting in a delay before we destory the shutdown the VR subsystem
-
-            // FIXME releasing the VR system at all seems to trigger an exception deep inside the Oculus DLL.  
-            // disabling for now.
-            //QTimer* releaseTimer = new QTimer();
-            //releaseTimer->singleShot(RELEASE_OPENVR_HMD_DELAY_MS, [releaseTimer] {
-            //    Lock lock(mutex);
-            //    qDebug() << "Delayed openvr destroy activated";
-            //    if (0 == refCount && nullptr != activeHmd) {
-            //        qDebug() << "Delayed openvr destroy: releasing resources";
-            //        activeHmd = nullptr;
-            //        vr::VR_Shutdown();
-            //    } else {
-            //        qDebug() << "Delayed openvr destroy: HMD still in use";
-            //    }
-            //    releaseTimer->deleteLater();
-            //});
         }
     }
 }

plugins/openvr/src/ViveControllerManager.cpp

@@ -48,10 +48,7 @@ static const QString RENDER_CONTROLLERS = "Render Hand Controllers";
 const QString ViveControllerManager::NAME = "OpenVR";
 
 bool ViveControllerManager::isSupported() const {
-    auto hmd = acquireOpenVrSystem();
+    return vr::VR_IsHmdPresent();
-    bool success = hmd != nullptr;
-    releaseOpenVrSystem();
-    return success;
 }
 
 void ViveControllerManager::activate() {