From 338d94197c36b30af09377ba4da7fc5dfc181461 Mon Sep 17 00:00:00 2001
From: Matt Van Horn <mvanhorn@users.noreply.github.com>
Date: Sat, 3 Oct 2026 11:51:30 -0700
Subject: [PATCH] Settle frame pacing after an inconsistent vsync gate (#2197)

---
 .../angelica/rendering/PacerCore.java         |  5 +-
 .../angelica/rendering/PacerCoreTest.java     | 57 +++++++++++++++++++
 2 files changed, 61 insertions(+), 1 deletion(-)

diff --git a/src/main/java/com/gtnewhorizons/angelica/rendering/PacerCore.java b/src/main/java/com/gtnewhorizons/angelica/rendering/PacerCore.java
index d616847fc..e8556eac8 100644
--- a/src/main/java/com/gtnewhorizons/angelica/rendering/PacerCore.java
+++ b/src/main/java/com/gtnewhorizons/angelica/rendering/PacerCore.java
@@ -63,6 +63,7 @@ final class PacerCore {
     private boolean locked;
     private boolean probing;
     private boolean probeExhausted;
+    private boolean gateAbandoned;
     private long probeLeadNanos;
     private boolean haveCandidate;
     private long candidateEndNanos;
@@ -336,7 +337,7 @@ final class PacerCore {
             if (locked && framesSinceCandidate >= LOCK_FRAMES) dropLock();
             return;
         }
-        if (haveCandidate && framesSinceCandidate <= LOCK_WINDOW) {
+        if (!gateAbandoned && haveCandidate && framesSinceCandidate <= LOCK_WINDOW) {
             final long delta = sampleEnd - candidateEndNanos;
             final long k = (delta + refreshPeriodNanos / 2) / refreshPeriodNanos;
             if (k >= 1L && Math.abs(delta - k * refreshPeriodNanos) <= refreshPeriodNanos / LOCK_TOL_DIVISOR) {
@@ -347,6 +348,7 @@ final class PacerCore {
                 if (++inconsistentPairs >= LOCK_WINDOW) {
                     dropLock();
                     probeExhausted = true;
+                    gateAbandoned = true;
                 }
             }
         }
@@ -358,6 +360,7 @@ final class PacerCore {
     private void armProbe() {
         probeLeadNanos = 0L;
         probeExhausted = false;
+        gateAbandoned = false;
     }
 
     private void dropLock() {
diff --git a/src/test/java/com/gtnewhorizons/angelica/rendering/PacerCoreTest.java b/src/test/java/com/gtnewhorizons/angelica/rendering/PacerCoreTest.java
index 5935a9ab9..68b51ce21 100644
--- a/src/test/java/com/gtnewhorizons/angelica/rendering/PacerCoreTest.java
+++ b/src/test/java/com/gtnewhorizons/angelica/rendering/PacerCoreTest.java
@@ -172,6 +172,51 @@ class PacerCoreTest {
         assertFalse(rig.core.probing(), "a gate proven off the grid must not be probed again");
     }
 
+    @Test
+    void anAbandonedGateStaysRetiredThroughAnotherOnGridRun() {
+        final Rig rig = new Rig(P60, true, 120);
+        rig.feedRun(PacerCore.LOCK_PAIRS + 1, 20 * MS, 5 * MS, P60);
+        assertTrue(rig.core.locked());
+        assertEquals(60, rig.core.effectiveCapHz());
+
+        long end = 20 * MS + (PacerCore.LOCK_PAIRS + 1) * P60;
+        for (int i = 0; i < PacerCore.LOCK_WINDOW + 1; i++) {
+            end += P60 / 2;
+            rig.feed(end, 5 * MS, end);
+        }
+        assertFalse(rig.core.locked());
+        assertFalse(rig.core.probing());
+
+        for (int i = 0; i < PacerCore.LOCK_PAIRS + 1; i++) {
+            end += P60;
+            rig.feed(end, 5 * MS, end);
+        }
+        assertFalse(rig.core.locked(), "a retired inconsistent gate must not lock again");
+        assertFalse(rig.core.probing());
+    }
+
+    @Test
+    void invalidateClearsAnAbandonedGate() {
+        final Rig rig = new Rig(P60, true, 120);
+        rig.feedRun(PacerCore.LOCK_PAIRS + 1, 20 * MS, 5 * MS, P60);
+
+        long end = 20 * MS + (PacerCore.LOCK_PAIRS + 1) * P60;
+        for (int i = 0; i < PacerCore.LOCK_WINDOW + 1; i++) {
+            end += P60 / 2;
+            rig.feed(end, 5 * MS, end);
+        }
+        assertFalse(rig.core.locked());
+        assertFalse(rig.core.probing());
+
+        rig.core.invalidate();
+        for (int i = 0; i < PacerCore.LOCK_PAIRS + 1; i++) {
+            end += P60;
+            rig.feed(end, 5 * MS, end);
+        }
+        assertTrue(rig.core.locked());
+        assertFalse(rig.core.probing());
+    }
+
     @Test
     void samplesFurtherApartThanTheLockWindowNeverPairUp() {
         final Rig rig = new Rig(P60, true, 0);
@@ -372,6 +417,18 @@ class PacerCoreTest {
         assertEquals(P60, rig.presents.get(300) - rig.presents.get(299), "an expired probe must fall back to the exact cadence");
     }
 
+    @Test
+    void anExpiredProbeLeadStillLocksWhenTheGateArrives() {
+        final Rig rig = new Rig(P60, true, 0);
+        for (int i = 0; i < 20; i++) rig.frame(4 * MS);
+        assertFalse(rig.core.locked());
+        assertFalse(rig.core.probing());
+
+        rig.feedRun(PacerCore.LOCK_PAIRS + 1, 20 * MS, 5 * MS, P60);
+        assertTrue(rig.core.locked());
+        assertFalse(rig.core.probing());
+    }
+
     @Test
     void mailboxIsNeverProbedAndNeverLocks() {
         final Rig rig = new Rig(P60, true, false, 0);