From ee25d7be38f47d229129456332ed7e2aeae44511 Mon Sep 17 00:00:00 2001
From: Mads Buvik Sandvei <madssandvei@protonmail.com>
Date: Sun, 24 May 2020 18:20:57 +0200
Subject: [PATCH] Prediction fix

---
 apps/openmw/mwvr/vrsession.cpp | 5 ++++-
 apps/openmw/mwvr/vrsession.hpp | 3 +++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/apps/openmw/mwvr/vrsession.cpp b/apps/openmw/mwvr/vrsession.cpp
index 3706fde08..7d31af1cb 100644
--- a/apps/openmw/mwvr/vrsession.cpp
+++ b/apps/openmw/mwvr/vrsession.cpp
@@ -118,6 +118,9 @@ void VRSession::swapBuffers(osg::GraphicsContext* gc, VRViewer& viewer)
 
     xr->endFrame(mPostdrawFrame->mPredictedDisplayTime, 1, &layerStack);
     mLastRenderedFrame = mPostdrawFrame->mFrameNo;
+    auto now = std::chrono::steady_clock::now();
+    mLastFrameInterval = std::chrono::duration_cast<std::chrono::nanoseconds>(now - mLastRenderedFrameTimestamp);
+    mLastRenderedFrameTimestamp = now;
 }
 
 void VRSession::advanceFramePhase(void)
@@ -148,7 +151,7 @@ void VRSession::startFrame()
     }
     else if (mFrames > mLastRenderedFrame)
     {
-        predictedDisplayTime = frameState.predictedDisplayTime + frameState.predictedDisplayPeriod;
+        predictedDisplayTime = frameState.predictedDisplayTime + mLastFrameInterval.count() * (mFrames - mLastRenderedFrame);
     }
 
     if (mFrames == 0 || predictedDisplayTime == 0)
diff --git a/apps/openmw/mwvr/vrsession.hpp b/apps/openmw/mwvr/vrsession.hpp
index f235eec65..ceb769482 100644
--- a/apps/openmw/mwvr/vrsession.hpp
+++ b/apps/openmw/mwvr/vrsession.hpp
@@ -73,6 +73,9 @@ public:
     long long mFrames{ 0 };
     long long mLastRenderedFrame{ 0 };
 
+    std::chrono::nanoseconds mLastFrameInterval{};
+    std::chrono::steady_clock::time_point mLastRenderedFrameTimestamp{std::chrono::steady_clock::now()};
+
     float mPlayerScale{ 1.f };
 };