From b03c941b8b0ab51227aa52d10616dbd47f75e5d9 Mon Sep 17 00:00:00 2001
From: 3gg <3gg@shellblade.net>
Date: Sat, 2 May 2026 14:58:00 -0700
Subject: Handle large time spikes

---
 simloop/src/simloop.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

(limited to 'simloop/src')

diff --git a/simloop/src/simloop.c b/simloop/src/simloop.c
index d231ab3..4fa5f62 100644
--- a/simloop/src/simloop.c
+++ b/simloop/src/simloop.c
@@ -31,15 +31,23 @@ void simloop_update(Simloop* sim, simloop_time_t dt, SimloopOut* out) {
   sim->clock += dt;
 
   // Simulation update.
-  // If the update falls behind the clock, we advance by a single ddt increment
-  // per loop iteration here and give it a chance to catch up over subsequent
-  // iterations.
+  // If the simulation falls behind the clock, we advance by a single ddt
+  // increment per loop iteration here and give it a chance to catch up over
+  // subsequent iterations.
   // This has the implication that percent_frame can fall out of range (>1) if
-  // we are not careful with how it is defined. See the general update function
-  // below.
-  const simloop_time_t delta            = sim->clock - sim->update.time;
-  const bool           update_this_tick = delta >= sim->update.ddt;
-  sim->update.time += update_this_tick ? sim->update.ddt : 0;
+  // we are not careful with how it is defined. See the logic below.
+  // If the delta is too large, then we simply warp the simulation to the wall
+  // clock. This avoids the appearance of the simulation playing in fast-forward
+  // as it tries to catch up. Large time spikes can typically occur at the start
+  // of the simulation when the application loads assets, compiles shaders, etc.
+  static const uint64_t max_catchup_frames = 10;
+  const simloop_time_t  delta              = sim->clock - sim->update.time;
+  const uint64_t        delta_frames       = delta / sim->update.ddt;
+  const bool            update_this_tick   = delta >= sim->update.ddt;
+  const bool            warp               = delta_frames > max_catchup_frames;
+  sim->update.time =
+      warp ? sim->clock
+           : (sim->update.time + (update_this_tick ? sim->update.ddt : 0));
 
   // Loop-state update.
   sim->frame += (update_this_tick ? 1 : 0);
-- 
cgit v1.2.3