From 7df82e4fee4204513615864b1a0c337959427589 Mon Sep 17 00:00:00 2001
From: catbot <catbot@bot.local>
Date: Thu, 18 Jun 2026 14:00:58 +0000
Subject: [PATCH] perf(window): block message loop while paused on Win32 (#134)
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When `updating` is false (paused / minimized / stopped), the FIFO
present no longer paces StartSync()'s message loop, so the bare
PeekMessage(PM_REMOVE) spin pinned a core at 100% while uselessly
re-running Gamepad::Tick() (mutex + per-pad COM reads) and
onBeforeUpdate every iteration.

Block on MsgWaitForMultipleObjectsEx with a short timeout while
!updating: the loop now wakes on input or every ~16ms, eliminating the
busy-spin while preserving gamepad polling / onBeforeUpdate at a sane
rate (e.g. to detect a controller button asking to resume). The
updating path is unchanged — present remains vsync-gated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
---
 implementations/Crafter.Graphics-Window.cpp | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/implementations/Crafter.Graphics-Window.cpp b/implementations/Crafter.Graphics-Window.cpp
index 19f1f55..3891db7 100644
--- a/implementations/Crafter.Graphics-Window.cpp
+++ b/implementations/Crafter.Graphics-Window.cpp
@@ -698,7 +698,20 @@ void Window::StartSync() {
 	}
     #endif
     #ifdef CRAFTER_GRAPHICS_WINDOW_WIN32
+    // While updating, the FIFO present inside Update() paces this loop to the
+    // vblank, so the PeekMessage poll is vsync-gated. While NOT updating
+    // (paused / minimized / stopped) nothing throttles the loop, and a bare
+    // PeekMessage(PM_REMOVE) spin pins a core at 100% while uselessly re-running
+    // Gamepad::Tick() (mutex + per-pad COM reads) and onBeforeUpdate every
+    // iteration. Block on the message queue instead, waking on input or after a
+    // short timeout so gamepad polling / onBeforeUpdate still tick at a sane
+    // rate (e.g. to detect a controller button asking to resume).
+    constexpr DWORD kPausedPollIntervalMs = 16;
     while(open) {
+        if (!updating) {
+            MsgWaitForMultipleObjectsEx(0, nullptr, kPausedPollIntervalMs,
+                                        QS_ALLINPUT, MWMO_INPUTAVAILABLE);
+        }
         MSG msg;
         while (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) {
             TranslateMessage(&msg);