From 1b78384da3d6c164d0c70582a20b3c1bda568a7e Mon Sep 17 00:00:00 2001
From: Geoffrey McRae <geoff@hostfission.com>
Date: Thu, 6 Aug 2026 17:11:03 +1000
Subject: [PATCH] [client] wayland: publish stable presentation cadence

---
 client/displayservers/Wayland/output.c       | 14 +++++++++++++-
 client/displayservers/Wayland/presentation.c | 11 ++++++++---
 client/displayservers/Wayland/wayland.h      |  4 +++-
 client/displayservers/Wayland/window.c       |  2 ++
 4 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/client/displayservers/Wayland/output.c b/client/displayservers/Wayland/output.c
index 43e4eb71..499ba017 100644
--- a/client/displayservers/Wayland/output.c
+++ b/client/displayservers/Wayland/output.c
@@ -325,6 +325,7 @@ static void outputDoneHandler(void * opaque, struct wl_output * output)
 {
   struct WaylandOutput * node = opaque;
   outputUpdateScale(node);
+  waylandOutputUpdateFramePeriod();
 }
 
 static void outputScaleHandler(void * opaque, struct wl_output * output, int32_t scale)
@@ -401,6 +402,7 @@ void waylandOutputFree(void)
     wl_list_remove(&node->link);
     free(node);
   }
+  atomic_store_explicit(&wlWm.nominalPeriod, 0, memory_order_release);
 }
 
 void waylandOutputBind(uint32_t name, uint32_t version)
@@ -470,6 +472,7 @@ void waylandOutputTryUnbind(uint32_t name)
       free(node);
       waylandWindowUpdateScale();
       waylandOutputUpdateHDRWhiteLevel();
+      waylandOutputUpdateFramePeriod();
       break;
     }
   }
@@ -485,7 +488,7 @@ struct WaylandScale waylandOutputGetScale(struct wl_output * output)
   return waylandScaleFromInt(0);
 }
 
-bool waylandOutputGetFramePeriod(uint64_t * period)
+void waylandOutputUpdateFramePeriod(void)
 {
   uint64_t fastest = 0;
   struct SurfaceOutput * surfaceOutput;
@@ -502,6 +505,15 @@ bool waylandOutputGetFramePeriod(uint64_t * period)
       fastest = candidate;
   }
 
+  atomic_store_explicit(
+      &wlWm.nominalPeriod, fastest, memory_order_release);
+}
+
+bool waylandOutputGetFramePeriod(uint64_t * period)
+{
+  const uint64_t fastest = atomic_load_explicit(
+      &wlWm.nominalPeriod, memory_order_acquire);
+
   if (!fastest)
     return false;
 
diff --git a/client/displayservers/Wayland/presentation.c b/client/displayservers/Wayland/presentation.c
index be5fa98d..c850c875 100644
--- a/client/displayservers/Wayland/presentation.c
+++ b/client/displayservers/Wayland/presentation.c
@@ -39,6 +39,8 @@ static void presentationClockId(void * data,
     struct wp_presentation * presentation, uint32_t clkId)
 {
   wlWm.clkId = clkId;
+  atomic_store_explicit(
+      &wlWm.presentationClockValid, true, memory_order_release);
 }
 
 static const struct wp_presentation_listener presentationListener = {
@@ -56,8 +58,6 @@ static void presentationFeedbackPresented(void * opaque,
     uint32_t tvNsec, uint32_t refresh, uint32_t seqHi, uint32_t seqLo, uint32_t flags)
 {
   struct FrameData * data = opaque;
-  if (refresh)
-    atomic_store(&wlWm.presentationPeriod, refresh);
   struct timespec present = {
     .tv_sec = (uint64_t) tvSecHi << 32 | tvSecLo,
     .tv_nsec = tvNsec,
@@ -96,6 +96,8 @@ bool waylandPresentationInit(void)
 {
   if (wlWm.presentation)
   {
+    atomic_store_explicit(
+        &wlWm.presentationClockValid, false, memory_order_release);
     wlWm.photonTimings = ringbuffer_new(256, sizeof(float));
     wlWm.photonGraph   = app_registerGraph("PHOTON", wlWm.photonTimings,
         0.0f, 30.0f, NULL);
@@ -110,6 +112,8 @@ void waylandPresentationFree(void)
   if (!wlWm.presentation)
     return;
 
+  atomic_store_explicit(
+      &wlWm.presentationClockValid, false, memory_order_release);
   wp_presentation_destroy(wlWm.presentation);
   app_unregisterGraph(wlWm.photonGraph);
   ringbuffer_free(&wlWm.photonTimings);
@@ -117,7 +121,8 @@ void waylandPresentationFree(void)
 
 void waylandPresentationFrame(void)
 {
-  if (!wlWm.presentation)
+  if (!wlWm.presentation || !atomic_load_explicit(
+        &wlWm.presentationClockValid, memory_order_acquire))
     return;
 
   struct FrameData * data = malloc(sizeof(*data));
diff --git a/client/displayservers/Wayland/wayland.h b/client/displayservers/Wayland/wayland.h
index 44fd8bb2..fb64ca02 100644
--- a/client/displayservers/Wayland/wayland.h
+++ b/client/displayservers/Wayland/wayland.h
@@ -161,7 +161,8 @@ struct WaylandDSState
 
   struct wp_presentation * presentation;
   clockid_t clkId;
-  _Atomic(uint64_t) presentationPeriod;
+  _Atomic(bool) presentationClockValid;
+  _Atomic(uint64_t) nominalPeriod;
   RingBuffer photonTimings;
   GraphHandle photonGraph;
 
@@ -397,6 +398,7 @@ void waylandOutputBind(uint32_t name, uint32_t version);
 void waylandOutputTryUnbind(uint32_t name);
 struct WaylandScale waylandOutputGetScale(struct wl_output * output);
 bool waylandOutputGetFramePeriod(uint64_t * period);
+void waylandOutputUpdateFramePeriod(void);
 void waylandOutputColorMgmtInit(struct WaylandOutput * output);
 void waylandOutputColorMgmtInitAll(void);
 void waylandOutputUpdateHDRWhiteLevel(void);
diff --git a/client/displayservers/Wayland/window.c b/client/displayservers/Wayland/window.c
index 2bd367c2..d5c80cb9 100644
--- a/client/displayservers/Wayland/window.c
+++ b/client/displayservers/Wayland/window.c
@@ -92,6 +92,7 @@ static void wlSurfaceEnterHandler(void * data, struct wl_surface * surface, stru
   wl_list_insert(&wlWm.surfaceOutputs, &node->link);
   waylandWindowUpdateScale();
   waylandOutputUpdateHDRWhiteLevel();
+  waylandOutputUpdateFramePeriod();
 }
 
 static void wlSurfaceLeaveHandler(void * data, struct wl_surface * surface, struct wl_output * output)
@@ -106,6 +107,7 @@ static void wlSurfaceLeaveHandler(void * data, struct wl_surface * surface, stru
     }
   waylandWindowUpdateScale();
   waylandOutputUpdateHDRWhiteLevel();
+  waylandOutputUpdateFramePeriod();
 }
 
 static const struct wl_surface_listener wlSurfaceListener = {