From a67c5221e327950855a6cc70ade245d548bcba06 Mon Sep 17 00:00:00 2001
From: Zach Pomerantz <zach@highfidelity.io>
Date: Thu, 18 Aug 2016 18:40:53 -0700
Subject: [PATCH 1/2] flush openvr fence before looking for it

---
 plugins/openvr/src/OpenVrDisplayPlugin.cpp | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/plugins/openvr/src/OpenVrDisplayPlugin.cpp b/plugins/openvr/src/OpenVrDisplayPlugin.cpp
index e751427ce2..8818cce628 100644
--- a/plugins/openvr/src/OpenVrDisplayPlugin.cpp
+++ b/plugins/openvr/src/OpenVrDisplayPlugin.cpp
@@ -111,12 +111,17 @@ public:
         _plugin.withNonPresentThreadLock([&] {
             while (!_queue.empty()) {
                 auto& front = _queue.front();
+
                 auto result = glClientWaitSync(front.fence, 0, 0);
-                if (GL_TIMEOUT_EXPIRED == result && GL_WAIT_FAILED == result) {
+
+                if (GL_TIMEOUT_EXPIRED == result || GL_WAIT_FAILED == result) {
                     break;
+                } else if (GL_CONDITION_SATISFIED == result || GL_CONDITION_SATISFIED == result) {
+                    glDeleteSync(front.fence);
+                } else {
+                    assert(false);
                 }
 
-                glDeleteSync(front.fence);
                 front.fence = 0;
                 _current = front;
                 _queue.pop();
@@ -455,6 +460,16 @@ void OpenVrDisplayPlugin::compositeLayers() {
 
 #if OPENVR_THREADED_SUBMIT
     newComposite.fence = glFenceSync(GL_SYNC_GPU_COMMANDS_COMPLETE, 0);
+    // https://www.opengl.org/registry/specs/ARB/sync.txt:
+    // > The simple flushing behavior defined by
+    // > SYNC_FLUSH_COMMANDS_BIT will not help when waiting for a fence
+    // > command issued in another context's command stream to complete.
+    // > Applications which block on a fence sync object must take
+    // > additional steps to assure that the context from which the
+    // > corresponding fence command was issued has flushed that command
+    // > to the graphics pipeline.
+    glFlush();
+
     if (!newComposite.textureID) {
         newComposite.textureID = getGLBackend()->getTextureID(newComposite.texture, false);
     }

From dbb916e2d9f56b6ec158c528ce48221217798706 Mon Sep 17 00:00:00 2001
From: Zach Pomerantz <zach@highfidelity.io>
Date: Mon, 22 Aug 2016 13:59:18 -0700
Subject: [PATCH 2/2] fix redundant openvr fence condition

---
 plugins/openvr/src/OpenVrDisplayPlugin.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/plugins/openvr/src/OpenVrDisplayPlugin.cpp b/plugins/openvr/src/OpenVrDisplayPlugin.cpp
index 8818cce628..0cb95e5747 100644
--- a/plugins/openvr/src/OpenVrDisplayPlugin.cpp
+++ b/plugins/openvr/src/OpenVrDisplayPlugin.cpp
@@ -116,7 +116,7 @@ public:
 
                 if (GL_TIMEOUT_EXPIRED == result || GL_WAIT_FAILED == result) {
                     break;
-                } else if (GL_CONDITION_SATISFIED == result || GL_CONDITION_SATISFIED == result) {
+                } else if (GL_CONDITION_SATISFIED == result || GL_ALREADY_SIGNALED == result) {
                     glDeleteSync(front.fence);
                 } else {
                     assert(false);