From 896a6ef5959043db5463637d84ed524ae7bade1e Mon Sep 17 00:00:00 2001
From: 3gg <3gg@shellblade.net>
Date: Sat, 11 Apr 2026 16:35:25 -0700
Subject: Render only if there was an update

---
 simloop/src/simloop.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

(limited to 'simloop/src')

diff --git a/simloop/src/simloop.c b/simloop/src/simloop.c
index aa2b6b7..606f5ed 100644
--- a/simloop/src/simloop.c
+++ b/simloop/src/simloop.c
@@ -19,6 +19,7 @@ Simloop simloop_make(const SimloopArgs* args) {
                                       .last_step = args->timer->start_time},
       .timer      = args->timer,
       .first_iter = true,
+      .updates_since_last_render = false,
   };
 }
 
@@ -57,11 +58,19 @@ void simloop_update(Simloop* sim, SimloopOut* out) {
   assert(sim);
   assert(out);
 
-  out->should_update = step_update(sim, &sim->update);
-  out->should_render =
-      step_render(sim, &sim->render) ||
+  // Simulation update.
+  const bool updated             = step_update(sim, &sim->update);
+  out->should_update             = updated;
+  sim->updates_since_last_render = sim->updates_since_last_render || updated;
+  // Simulation render.
+  const bool rendered =
+      (sim->updates_since_last_render && step_render(sim, &sim->render)) ||
       (sim->first_iter); // Trigger an initial render on the first frame.
-  sim->frame += (out->should_update ? 1 : 0);
+  out->should_render = rendered;
+  sim->updates_since_last_render =
+      sim->updates_since_last_render && !out->should_render;
+  // Loop state update.
+  sim->frame += (updated ? 1 : 0);
   sim->first_iter     = false;
   out->frame          = sim->frame;
   out->render_elapsed = time_elapsed(sim, sim->render.last_step);
-- 
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