From 12f6485e528f8d1dba3d89f6de502be2e6cd3722 Mon Sep 17 00:00:00 2001
From: Geoffrey McRae <geoff@hostfission.com>
Date: Wed, 5 Aug 2026 11:52:44 +1000
Subject: [PATCH] [client/obs] scheduler: correct phase feedback

Only report the client queue lead when JIT rendering provides a valid
measurement. Clamp linear phase errors instead of wrapping them into the
opposite direction at half of a refresh period.

Timestamp OBS frames after the shared framebuffer becomes ready.
---
 client/src/frame_scheduler.c | 10 +++++-----
 client/src/main.c            | 13 ++++---------
 obs/frame_scheduler.c        | 10 +++++-----
 obs/lg.c                     | 17 +++++++++++------
 4 files changed, 25 insertions(+), 25 deletions(-)

diff --git a/client/src/frame_scheduler.c b/client/src/frame_scheduler.c
index b6a0f8dc..2e1c3748 100644
--- a/client/src/frame_scheduler.c
+++ b/client/src/frame_scheduler.c
@@ -262,11 +262,11 @@ void frameScheduler_feedback(uint64_t frameSerial, uint32_t generation,
   int64_t error = measuredPhase > FRAME_SCHEDULER_TARGET_SLACK_NS ?
     (int64_t)(measuredPhase - FRAME_SCHEDULER_TARGET_SLACK_NS) :
     -(int64_t)(FRAME_SCHEDULER_TARGET_SLACK_NS - measuredPhase);
-  error %= period;
-  if (error > period / 2)
-    error -= period;
-  else if (error < -period / 2)
-    error += period;
+  const int64_t limit = period / 2;
+  if (error > limit)
+    error = limit;
+  else if (error < -limit)
+    error = -limit;
 
   if (!l_frameScheduler.feedbackSamples)
     l_frameScheduler.phaseError = error;
diff --git a/client/src/main.c b/client/src/main.c
index 1e2cf021..716f6da5 100644
--- a/client/src/main.c
+++ b/client/src/main.c
@@ -434,17 +434,12 @@ static void frameTimingFinishRender(const LG_RendererFrameTiming * timing,
   }
   LG_UNLOCK(l_frameTiming.lock);
 
-  if (feedbackFrameSerial && feedbackGeneration)
+  if (g_state.jitRender && feedbackFrameSerial && feedbackGeneration &&
+      feedbackQueueStart && prepareStart >= feedbackQueueStart)
   {
-    uint64_t measuredPhase = timing->swapTime;
-    if (g_state.jitRender)
-    {
-      if (!feedbackQueueStart || prepareStart < feedbackQueueStart)
-        return;
-      measuredPhase = prepareStart - feedbackQueueStart;
-    }
     frameScheduler_feedback(
-        feedbackFrameSerial, feedbackGeneration, measuredPhase);
+        feedbackFrameSerial, feedbackGeneration,
+        prepareStart - feedbackQueueStart);
   }
 }
 
diff --git a/obs/frame_scheduler.c b/obs/frame_scheduler.c
index 0cd57426..4627d641 100644
--- a/obs/frame_scheduler.c
+++ b/obs/frame_scheduler.c
@@ -98,11 +98,11 @@ void lgFrameSchedulerFeedback(LGFrameScheduler * scheduler,
     (int64_t)(measuredPhase - FRAME_SCHEDULER_TARGET_SLACK_NS) :
     -(int64_t)(FRAME_SCHEDULER_TARGET_SLACK_NS - measuredPhase);
   const int64_t period = (int64_t)scheduler->period;
-  error %= period;
-  if (error > period / 2)
-    error -= period;
-  else if (error < -period / 2)
-    error += period;
+  const int64_t limit = period / 2;
+  if (error > limit)
+    error = limit;
+  else if (error < -limit)
+    error = -limit;
 
   if (!scheduler->feedbackSamples)
     scheduler->phaseError = error;
diff --git a/obs/lg.c b/obs/lg.c
index 496f79cf..45c2110f 100644
--- a/obs/lg.c
+++ b/obs/lg.c
@@ -505,15 +505,22 @@ static void * frameThread(void * data)
       }
     }
 
-    const uint64_t now = os_gettime_ns();
+    uint64_t now = os_gettime_ns();
     if (status == LGMP_OK)
     {
       LGMPMessage msg;
       if (lgmpClientProcess(this->frameQueue, &msg) == LGMP_OK)
       {
-        const KVMFRFrame * frame = (const KVMFRFrame *)msg.mem;
-        lgFrameSchedulerObserveFrame(&this->frameScheduler,
-          frame->frameSerial, msg.udata, now);
+        const KVMFRFrame  * frame = (const KVMFRFrame *)msg.mem;
+        const FrameBuffer * fb =
+          (const FrameBuffer *)((const uint8_t *)frame + frame->offset);
+        if (framebuffer_wait(
+              fb, (size_t)frame->dataHeight * frame->pitch))
+        {
+          now = os_gettime_ns();
+          lgFrameSchedulerObserveFrame(&this->frameScheduler,
+            frame->frameSerial, msg.udata, now);
+        }
       }
     }
 
@@ -1287,8 +1294,6 @@ static void lgVideoTick(void * data, float seconds)
   }
 
   const KVMFRFrame * frame = (KVMFRFrame *)msg.mem;
-  lgFrameSchedulerObserveFrame(&this->frameScheduler,
-    frame->frameSerial, msg.udata, tickTime);
   lgFrameSchedulerFeedback(&this->frameScheduler,
     frame->frameSerial, msg.udata, tickTime);