Move input polling to its own thread; fixed-width fast-changing UI numbers

Input thread: controller polling, pad publishing, and rumble forwarding were
driven by the render loop, so a low/synced frame rate throttled how often guest
input reached the game. New InputWorker owns the InputSource and runs poll +
IPC publish + rumble on a dedicated ~1 kHz thread, independent of rendering. The
UI thread reads a copy-safe InputSnapshot for the Controllers panel and relays the
Steam-Input request/active/failed state to/from the worker (Steam init/shutdown now
happen on the worker thread). IpcServer gained a mutex so the worker's publish() /
hook_status() can't race the UI thread starting/stopping the shared-memory channel
(use-after-unmap); InjectionPanel::test_input_ is now atomic. ControllersPanel::draw
takes an InputSnapshot instead of the live InputSource.

Fixed-width numbers: fast-changing readouts (menu-bar FPS/ms, Video pipeline rates +
latency + graph legend, controller poll rates + round-trip sticks, audio buffered ms
+ frames/s) printed with %.0f etc., so they shifted/blurred as values crossed digit
thresholds (99 -> 100) each frame. Padded them to fixed field widths so they stay put.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

host/CMakeLists.txt

@@ -9,6 +9,7 @@ add_executable(coop_host WIN32
 	src/log_panel.cpp
 	src/ui/app_chrome.cpp
 	src/input/xinput_source.cpp
+	src/input/input_worker.cpp
 	src/inject/process_list.cpp
 	src/inject/window_list.cpp
 	src/inject/injector.cpp

host/src/audio_panel.cpp

@@ -77,7 +77,7 @@ void AudioPanel::draw_ui(const HookStatusView& status, bool debug_details)
 		ImGui::SameLine();
 		ImGui::TextColored(hooked ? ImVec4(0.4f, 1.0f, 0.4f, 1.0f) : ImVec4(1.0f, 0.8f, 0.3f, 1.0f), "%s",
 		                   mirror_.source_name());
-		ImGui::Text("Buffered: %u ms", mirror_.buffered_ms());
+		ImGui::Text("Buffered: %4u ms", mirror_.buffered_ms());
 	}
 	const std::string mirror_status = mirror_.status();
 	if (!mirror_status.empty())
@@ -176,7 +176,7 @@ void AudioPanel::draw_ui(const HookStatusView& status, bool debug_details)
 			{
 				ImGui::TextColored(ImVec4(0.4f, 1.0f, 0.4f, 1.0f), "live");
 				ImGui::SameLine();
-				ImGui::TextDisabled("%.0f/s", frames_per_s_[i]);
+				ImGui::TextDisabled("%6.0f/s", frames_per_s_[i]);
 			}
 			else
 			{

host/src/capture_panel.cpp

@@ -188,13 +188,15 @@ void CapturePanel::draw_pipeline_metrics(const FrameStats& stats)
 	}
 	const double now = ImGui::GetTime();
 	ImGui::SeparatorText("Pipeline rates");
-	ImGui::Text("Tool render:  %.0f FPS  (%.2f ms)", stats.fps(), stats.avg_ms());
+	// Fixed field widths so fast-changing numbers don't jitter as they cross digit
+	// thresholds (e.g. 99 -> 100) frame to frame.
+	ImGui::Text("Tool render:  %4.0f FPS  (%6.2f ms)", stats.fps(), stats.avg_ms());
 
 	if (source_ == Source_Hooked)
 	{
 		const VideoShareView v = injection_ != nullptr ? injection_->video_share() : VideoShareView{};
-		ImGui::Text("Game present: %.0f /s", present_rate_.sample(v.present_calls, now));
+		ImGui::Text("Game present: %5.0f /s", present_rate_.sample(v.present_calls, now));
-		ImGui::Text("Hook publish: %.0f /s", capture_rate_.sample(v.generation, now));
+		ImGui::Text("Hook publish: %5.0f /s", capture_rate_.sample(v.generation, now));
 
 		// On each newly published frame, measure now - present_qpc (system-wide clock).
 		if (v.generation != last_video_gen_ && v.present_qpc != 0 && qpc_freq_ > 0)
@@ -234,7 +236,7 @@ void CapturePanel::draw_pipeline_metrics(const FrameStats& stats)
 		}
 		if (lat_avg_ > 0.0f)
 		{
-			ImGui::Text("Capture->display: avg %.1f  min %.1f  max %.1f ms", lat_avg_, lat_min_, lat_max_);
+			ImGui::Text("Capture->display: avg %6.1f  min %6.1f  max %6.1f ms", lat_avg_, lat_min_, lat_max_);
 		}
 		else
 		{
@@ -244,7 +246,7 @@ void CapturePanel::draw_pipeline_metrics(const FrameStats& stats)
 	else
 	{
 		ImGui::TextDisabled("Game present: n/a (WGC has no game frame timing)");
-		ImGui::Text("WGC capture:  %.0f /s", capture_rate_.sample(capture_.frames_arrived(), now));
+		ImGui::Text("WGC capture:  %5.0f /s", capture_rate_.sample(capture_.frames_arrived(), now));
 		ImGui::TextDisabled("Latency: n/a (WGC frames aren't game-timestamped)");
 	}
 }
@@ -319,7 +321,7 @@ void CapturePanel::draw_perf_graphs(const FrameStats& /*stats*/)
 	// Legend: a colored label + the latest value of each line, so colors map to series.
 	for (int i = 0; i < n; ++i)
 	{
-		ImGui::TextColored(cols[i], "%s %.0f", names[i], counts[i] > 0 ? fps[i][counts[i] - 1] : 0.0f);
+		ImGui::TextColored(cols[i], "%-4s %4.0f", names[i], counts[i] > 0 ? fps[i][counts[i] - 1] : 0.0f);
 		if (i + 1 < n)
 		{
 			ImGui::SameLine();

host/src/controllers_panel.cpp

@@ -67,12 +67,12 @@ void draw_pad(int index, const PadInfo& pad, bool debug_details)
 
 } // namespace
 
-void ControllersPanel::draw(const InputSource& input, const HookStatusView& status, bool debug_details)
+void ControllersPanel::draw(const InputSnapshot& input, const HookStatusView& status, bool debug_details)
 {
 	apply_panel_layout(Panel::Controllers);
 	ImGui::Begin("Controllers");
 
-	ImGui::Text("Input backend: %s", input.name());
+	ImGui::Text("Input backend: %s", input.backend);
 	ImGui::TextDisabled("This window is what Remote Play Together captures.");
 	ImGui::TextDisabled("F1: hide overlay (clean mirror)   Esc: quit");
 
@@ -108,7 +108,7 @@ void ControllersPanel::draw(const InputSource& input, const HookStatusView& stat
 
 	// --- Guest pads the host receives from RPT -----------------------------
 	ImGui::SeparatorText("Incoming (host receives)");
-	const auto& pads = input.pads();
+	const auto& pads = input.pads;
 	for (int i = 0; i < static_cast<int>(pads.size()); ++i)
 	{
 		draw_pad(i, pads[i], debug_details);
@@ -145,7 +145,7 @@ void ControllersPanel::draw(const InputSource& input, const HookStatusView& stat
 	}
 	if (total_rate > 0.0)
 	{
-		ImGui::TextColored(kGreen, "Game reading controller: %.0f polls/s", total_rate);
+		ImGui::TextColored(kGreen, "Game reading controller: %5.0f polls/s", total_rate);
 	}
 	else
 	{
@@ -168,7 +168,7 @@ void ControllersPanel::draw(const InputSource& input, const HookStatusView& stat
 			ImGui::TableNextColumn();
 			if (state_rate_[i] > 0.0)
 			{
-				ImGui::TextColored(kGreen, "%.0f", state_rate_[i]);
+				ImGui::TextColored(kGreen, "%5.0f", state_rate_[i]);
 			}
 			else
 			{
@@ -194,7 +194,7 @@ void ControllersPanel::draw(const InputSource& input, const HookStatusView& stat
 			ImGui::TableSetupColumn("Forwarded  btn / LX,LY");
 			ImGui::TableSetupColumn("Game read  btn / LX,LY");
 			ImGui::TableHeadersRow();
-			const auto& fwd = input.pads();
+			const auto& fwd = input.pads;
 			for (int i = 0; i < static_cast<int>(kMaxPads); ++i)
 			{
 				const CoopPadState& f = fwd[i].state;
@@ -203,10 +203,10 @@ void ControllersPanel::draw(const InputSource& input, const HookStatusView& stat
 				ImGui::TableNextColumn();
 				ImGui::Text("%d", i);
 				ImGui::TableNextColumn();
-				ImGui::Text("0x%04X  %d,%d", f.buttons, f.thumb_lx, f.thumb_ly);
+				ImGui::Text("0x%04X  %6d,%6d", f.buttons, f.thumb_lx, f.thumb_ly);
 				ImGui::TableNextColumn();
 				const bool match = f.buttons == r.buttons && f.thumb_lx == r.thumb_lx && f.thumb_ly == r.thumb_ly;
-				ImGui::TextColored(match ? kGreen : kGrey, "0x%04X  %d,%d", r.buttons, r.thumb_lx, r.thumb_ly);
+				ImGui::TextColored(match ? kGreen : kGrey, "0x%04X  %6d,%6d", r.buttons, r.thumb_lx, r.thumb_ly);
 			}
 			ImGui::EndTable();
 		}

host/src/controllers_panel.hpp

@@ -17,10 +17,11 @@ namespace coop
 class ControllersPanel
 {
 public:
+	// `input` is the input worker's latest snapshot (guest pads + active backend);
 	// `status` is the hook's back-channel (per-slot poll counters); `debug_details`
 	// reveals the raw axis values, the per-slot poll-rate table, and the synthetic
 	// test-input toggle.
-	void draw(const InputSource& input, const HookStatusView& status, bool debug_details);
+	void draw(const InputSnapshot& input, const HookStatusView& status, bool debug_details);
 
 	// Whether the operator enabled "Forward synthetic test input" (a controller debug
 	// aid). The host feeds this to InjectionPanel, which substitutes a synthetic pad.

host/src/injection_panel.cpp

@@ -256,7 +256,7 @@ void InjectionPanel::reattach()
 
 void InjectionPanel::publish(const std::array<PadInfo, kMaxPads>& pads)
 {
-	if (!test_input_)
+	if (!test_input_.load(std::memory_order_relaxed))
 	{
 		server_.publish(pads);
 		return;

host/src/injection_panel.hpp

@@ -3,6 +3,7 @@
 #pragma once
 
 #include <array>
+#include <atomic>
 #include <string>
 #include <vector>
 
@@ -52,7 +53,7 @@ public:
 	// panel (a controller-debug aid); the host feeds its state here each frame.
 	void set_test_input(bool on)
 	{
-		test_input_ = on;
+		test_input_.store(on, std::memory_order_relaxed);
 	}
 
 	// The injected game's main window, as reported by the hook (null if none). A
@@ -165,7 +166,9 @@ private:
 	std::string status_;
 	ImVec4 status_color_;
 
-	bool test_input_ = false;
+	// Written by the UI thread (set_test_input), read by the input worker thread
+	// (publish) -- atomic so that cross-thread read is well-defined.
+	std::atomic<bool> test_input_{false};
 
 	// Host-requested per-subsystem install state (default on). Written to the hook
 	// over the control channel; the hook reconciles each tick.

host/src/input/input_source.hpp

@@ -21,6 +21,16 @@ struct PadInfo
 	std::string source; // human-readable label for the debug overlay
 };
 
+// A copy-safe snapshot of the input backend's state, published by the input worker
+// thread for the UI to display. This decouples the Controllers panel (UI thread) from
+// the worker's live polling, so the worker can own its InputSource exclusively.
+struct InputSnapshot
+{
+	std::array<PadInfo, kMaxPads> pads{};
+	const char* backend = "XInput"; // backend name (static string literal; thread-safe to share)
+	bool steam_active = false;
+};
+
 class InputSource
 {
 public:

host/src/input/input_worker.cpp

@@ -0,0 +1,144 @@
+#include "input/input_worker.hpp"
+
+#include <chrono>
+#include <cstdint>
+#include <memory>
+
+#include "injection_panel.hpp"
+#include "input/xinput_source.hpp"
+
+#ifdef COOP_WITH_STEAM
+#include "input/steam_input_source.hpp"
+#endif
+
+namespace coop
+{
+
+InputWorker::~InputWorker()
+{
+	stop();
+}
+
+void InputWorker::start(InjectionPanel* injection, std::string steam_manifest)
+{
+	if (running_.load(std::memory_order_acquire))
+	{
+		return;
+	}
+	injection_ = injection;
+	steam_manifest_ = std::move(steam_manifest);
+	running_.store(true, std::memory_order_release);
+	thread_ = std::thread([this] { run(); });
+}
+
+void InputWorker::stop()
+{
+	running_.store(false, std::memory_order_release);
+	if (thread_.joinable())
+	{
+		thread_.join();
+	}
+}
+
+InputSnapshot InputWorker::snapshot() const
+{
+	std::scoped_lock lock(snapshot_mutex_);
+	return snapshot_;
+}
+
+void InputWorker::publish_snapshot(const InputSource& src, bool steam_active)
+{
+	std::scoped_lock lock(snapshot_mutex_);
+	snapshot_.pads = src.pads();
+	snapshot_.backend = src.name();
+	snapshot_.steam_active = steam_active;
+}
+
+void InputWorker::run()
+{
+	// The worker owns its input backend(s) exclusively, so no locking is needed around
+	// polling -- only the published snapshot and the IPC are shared with the UI thread.
+	XInputSource xinput;
+#ifdef COOP_WITH_STEAM
+	std::unique_ptr<SteamInputSource> steam;
+#endif
+	InputSource* active = &xinput;
+
+	// Last rumble forwarded per slot, so we only re-send on change.
+	std::uint16_t last_rumble_l[kMaxPads] = {};
+	std::uint16_t last_rumble_r[kMaxPads] = {};
+
+	while (running_.load(std::memory_order_relaxed))
+	{
+		const bool want_steam = want_steam_.load(std::memory_order_relaxed);
+#ifdef COOP_WITH_STEAM
+		// Reconcile the backend with the UI's request. Initializing Steam Input hijacks
+		// XInput, so it's strictly opt-in; a failed init falls back to plain XInput and
+		// flags steam_failed_ so the UI can reset its toggle (and a later retry is
+		// possible once the request is cleared).
+		if (want_steam && steam == nullptr && !steam_failed_.load(std::memory_order_relaxed))
+		{
+			steam = std::make_unique<SteamInputSource>();
+			if (steam->init(steam_manifest_))
+			{
+				active = steam.get();
+			}
+			else
+			{
+				steam.reset();
+				active = &xinput;
+				steam_failed_.store(true, std::memory_order_relaxed);
+			}
+		}
+		else if (!want_steam && steam != nullptr)
+		{
+			steam->shutdown();
+			steam.reset();
+			active = &xinput;
+		}
+		if (!want_steam)
+		{
+			steam_failed_.store(false, std::memory_order_relaxed); // allow a future retry
+		}
+		const bool steam_active = steam != nullptr;
+#else
+		(void)want_steam;
+		const bool steam_active = false;
+#endif
+
+		active->poll();
+
+		if (injection_ != nullptr)
+		{
+			// Push the latest pads to the game (publish() substitutes synthetic test input
+			// itself when that mode is on), then forward any newly requested rumble.
+			injection_->publish(active->pads());
+
+			const HookStatusView hs = injection_->hook_status();
+			for (int i = 0; i < static_cast<int>(kMaxPads); ++i)
+			{
+				if (hs.rumble_left[i] != last_rumble_l[i] || hs.rumble_right[i] != last_rumble_r[i])
+				{
+					active->set_rumble(i, hs.rumble_left[i], hs.rumble_right[i]);
+					last_rumble_l[i] = hs.rumble_left[i];
+					last_rumble_r[i] = hs.rumble_right[i];
+				}
+			}
+		}
+
+		publish_snapshot(*active, steam_active);
+
+		// ~1 ms cadence (timeBeginPeriod(1) in wWinMain keeps Sleep granular), so input
+		// is polled/forwarded at ~1 kHz regardless of the render frame rate.
+		std::this_thread::sleep_for(std::chrono::milliseconds(1));
+	}
+
+#ifdef COOP_WITH_STEAM
+	if (steam != nullptr)
+	{
+		steam->shutdown();
+	}
+#endif
+}
+
+} // namespace coop

host/src/input/input_worker.hpp

@@ -0,0 +1,68 @@
+// Runs controller polling + forwarding on its own thread, decoupled from the render
+// loop. The render frame rate (which can drop, especially with frame-sync) must not
+// throttle how often guest input is polled and pushed to the game, so this worker
+// owns the InputSource, polls it at a fixed high cadence, publishes pads to the
+// injected hook over IPC, and forwards game-requested rumble back to the guest pad.
+// The UI thread reads a copy-safe snapshot() for the Controllers panel.
+#pragma once
+
+#include <atomic>
+#include <mutex>
+#include <string>
+#include <thread>
+
+#include "input/input_source.hpp"
+
+namespace coop
+{
+
+class InjectionPanel;
+
+class InputWorker
+{
+public:
+	InputWorker() = default;
+	~InputWorker();
+
+	InputWorker(const InputWorker&) = delete;
+	InputWorker& operator=(const InputWorker&) = delete;
+
+	// Start the input thread. `injection` receives published pads and supplies the
+	// game's rumble requests; it must outlive this worker. `steam_manifest` is the
+	// Steam Input action-manifest path, used only if/when Steam Input is enabled
+	// (ignored in non-Steam builds). No-op if already running.
+	void start(InjectionPanel* injection, std::string steam_manifest);
+	void stop();
+
+	// UI -> worker: request the Steam Input backend (true) or plain XInput (false).
+	void set_want_steam(bool on)
+	{
+		want_steam_.store(on, std::memory_order_relaxed);
+	}
+
+	// worker -> UI: latest snapshot for the Controllers panel (thread-safe copy).
+	[[nodiscard]] InputSnapshot snapshot() const;
+
+	// worker -> UI: Steam Input was requested but failed to start (so the panel can
+	// reset its toggle and fall back to XInput). Cleared once Steam is not requested.
+	[[nodiscard]] bool steam_failed() const
+	{
+		return steam_failed_.load(std::memory_order_relaxed);
+	}
+
+private:
+	void run();
+	void publish_snapshot(const InputSource& src, bool steam_active);
+
+	std::thread thread_;
+	std::atomic<bool> running_{false};
+	std::atomic<bool> want_steam_{false};
+	std::atomic<bool> steam_failed_{false};
+	InjectionPanel* injection_ = nullptr;
+	std::string steam_manifest_;
+
+	mutable std::mutex snapshot_mutex_;
+	InputSnapshot snapshot_;
+};
+
+} // namespace coop

host/src/ipc/ipc_server.cpp

@@ -5,7 +5,8 @@ namespace coop
 
 bool IpcServer::start(unsigned long target_pid)
 {
-	stop();
+	std::scoped_lock lock(mutex_);
+	stop_locked();
 
 	if (!shm_.create(shared_memory_name(target_pid), sizeof(SharedBlock)))
 	{
@@ -36,6 +37,7 @@ bool IpcServer::start(unsigned long target_pid)
 
 void IpcServer::publish(const std::array<PadInfo, kMaxPads>& pads)
 {
+	std::scoped_lock lock(mutex_);
 	if (block_ == nullptr)
 	{
 		return;
@@ -51,6 +53,7 @@ void IpcServer::publish(const std::array<PadInfo, kMaxPads>& pads)
 
 HookStatusView IpcServer::hook_status() const
 {
+	std::scoped_lock lock(mutex_);
 	HookStatusView view;
 	if (block_ == nullptr)
 	{
@@ -96,6 +99,7 @@ HookStatusView IpcServer::hook_status() const
 
 VideoShareView IpcServer::video_share() const
 {
+	std::scoped_lock lock(mutex_);
 	VideoShareView v;
 	if (block_ == nullptr)
 	{
@@ -113,6 +117,7 @@ VideoShareView IpcServer::video_share() const
 
 void IpcServer::set_subsystem_enabled(std::uint32_t subsystem, bool enabled)
 {
+	std::scoped_lock lock(mutex_);
 	if (block_ != nullptr && subsystem < HookSubsys_Count)
 	{
 		// 0 = install, 1 = remove.
@@ -121,6 +126,12 @@ void IpcServer::set_subsystem_enabled(std::uint32_t subsystem, bool enabled)
 }
 
 void IpcServer::stop()
+{
+	std::scoped_lock lock(mutex_);
+	stop_locked();
+}
+
+void IpcServer::stop_locked()
 {
 	if (block_ != nullptr)
 	{

host/src/ipc/ipc_server.hpp

@@ -4,6 +4,7 @@
 
 #include <array>
 #include <cstdint>
+#include <mutex>
 
 #include "coop/log_ring.hpp"
 #include "coop/protocol.hpp"
@@ -82,6 +83,7 @@ public:
 	// silently if not started or the ring is full.
 	void push_mkb(const MkbEvent& ev)
 	{
+		std::scoped_lock lock(mutex_);
 		if (block_ != nullptr)
 		{
 			push_mkb_event(block_->mkb, ev);
@@ -92,6 +94,7 @@ public:
 	// (false, the default). No-op if not started.
 	void set_cursor_clip_allowed(bool allowed)
 	{
+		std::scoped_lock lock(mutex_);
 		if (block_ != nullptr)
 		{
 			block_->control.allow_cursor_clip.store(allowed ? 1u : 0u, std::memory_order_release);
@@ -119,6 +122,14 @@ public:
 	}
 
 private:
+	void stop_locked(); // tear-down body shared by start()/stop(); caller holds mutex_
+
+	// Guards the mapping pointer (block_) and its accesses. The input worker thread
+	// calls publish()/hook_status() while the UI thread may start()/stop() the channel
+	// (swapping/unmapping block_), so those must be mutually exclusive to avoid a
+	// use-after-unmap. Critical sections are tiny (a struct copy / memcpy).
+	mutable std::mutex mutex_;
+
 	SharedMemory shm_;
 	SharedBlock* block_ = nullptr;
 	unsigned long target_pid_ = 0;

host/src/main.cpp

@@ -6,7 +6,6 @@
 // this window via Windows Graphics Capture (Video mirror panel).
 
 #include <cstdint>
-#include <memory>
 
 #include <windows.h>
 
@@ -23,14 +22,12 @@
 #include "imgui_layer.hpp"
 #include "inject/mkb_forward.hpp"
 #include "injection_panel.hpp"
-#include "input/xinput_source.hpp"
+#include "input/input_worker.hpp"
 #include "log_panel.hpp"
 #include "ui/app_chrome.hpp"
 
 #ifdef COOP_WITH_STEAM
 #include <string>
-
-#include "input/steam_input_source.hpp"
 #endif
 
 namespace
@@ -125,17 +122,6 @@ int run()
 		return 1;
 	}
 
-	// XInput is the default guest-input path: Remote Play Together delivers guest
-	// pads as XInput, and it Just Works. Steam Input is opt-in (Controllers panel) --
-	// merely initializing it activates Steam's in-process XInput interception, which
-	// hides controllers from XInput unless they're bound to our action set for this
-	// app, so making it the default can silently break input. We switch the active
-	// backend at runtime to match the toggle.
-	coop::XInputSource xinput;
-	coop::InputSource* input = &xinput;
-#ifdef COOP_WITH_STEAM
-	std::unique_ptr<coop::SteamInputSource> steam;
-#endif
 	coop::ControllersPanel controllers;
 	coop::InjectionPanel injection;
 	coop::AudioPanel audio;
@@ -148,6 +134,19 @@ int run()
 	}
 	capture.set_injection(&injection); // for the Present-hook (Hooked) video source
 
+	// Controller polling + forwarding runs on its own thread so the render frame rate
+	// (which can drop, especially with frame-sync) never throttles input. XInput is the
+	// default guest path (RPT delivers guest pads as XInput and it Just Works); Steam
+	// Input is opt-in (Controllers panel) -- merely initializing it hijacks XInput and
+	// hides controllers unless they're bound to our action set, so it can silently break
+	// input. The worker reconciles the active backend with the toggle.
+	coop::InputWorker input_worker;
+#ifdef COOP_WITH_STEAM
+	input_worker.start(&injection, steam_manifest_path());
+#else
+	input_worker.start(&injection, std::string());
+#endif
+
 	// The overlay can be hidden (F1) so the window is a clean mirror for Remote
 	// Play Together; the pipelines keep running underneath either way.
 	bool show_overlay = true;
@@ -155,10 +154,6 @@ int run()
 	coop::UiState ui;
 	coop::FrameStats stats;
 
-	// Last rumble forwarded per slot, so we only re-send on change.
-	std::uint16_t last_rumble_l[coop::kMaxPads] = {};
-	std::uint16_t last_rumble_r[coop::kMaxPads] = {};
-
 	// Frame-sync: the hook generation we last presented (so we wait for the next one).
 	std::uint32_t last_synced_gen = 0;
 
@@ -174,51 +169,24 @@ int run()
 				break;
 			}
 		}
+
+		// Input polling, pad publishing, and rumble all run on the input worker thread;
+		// here we only relay UI requests to it and read back its snapshot for display.
+		const coop::InputSnapshot input_snapshot = input_worker.snapshot();
 #ifdef COOP_WITH_STEAM
-		// Switch the active input backend to match the Controllers-panel toggle.
+		input_worker.set_want_steam(controllers.steam_input_requested());
-		const bool want_steam = controllers.steam_input_requested();
+		if (input_worker.steam_failed())
-		if (want_steam && steam == nullptr)
 		{
-			steam = std::make_unique<coop::SteamInputSource>();
+			controllers.on_steam_init_failed(); // resets the toggle; worker falls back to XInput
-			if (steam->init(steam_manifest_path()))
-			{
-				input = steam.get();
-				controllers.set_steam_active(true);
-			}
-			else
-			{
-				steam.reset();
-				controllers.on_steam_init_failed();
-			}
 		}
-		else if (!want_steam && steam != nullptr)
+		else
 		{
-			steam->shutdown();
+			controllers.set_steam_active(input_snapshot.steam_active);
-			steam.reset();
-			input = &xinput;
-			controllers.set_steam_active(false);
 		}
 #endif
-		input->poll();
 		injection.set_test_input(controllers.test_input()); // toggle lives in the Controllers panel
-		injection.publish(input->pads());
 		injection.tick(); // refresh target liveness before the mirror panels read game_hwnd()
 
-		// Forward the rumble the game requested back to the guest's controller (only
-		// when it changes, to avoid spamming XInputSetState / TriggerVibration).
-		{
-			const coop::HookStatusView hs = injection.hook_status();
-			for (int i = 0; i < static_cast<int>(coop::kMaxPads); ++i)
-			{
-				if (hs.rumble_left[i] != last_rumble_l[i] || hs.rumble_right[i] != last_rumble_r[i])
-				{
-					input->set_rumble(i, hs.rumble_left[i], hs.rumble_right[i]);
-					last_rumble_l[i] = hs.rumble_left[i];
-					last_rumble_r[i] = hs.rumble_right[i];
-				}
-			}
-		}
-
 		const HWND game = injection.game_hwnd();
 		capture.set_target(game);
 		audio.set_target(game);
@@ -245,7 +213,7 @@ int run()
 			coop::draw_main_menu_bar(ui, stats);
 			if (ui.show_controllers)
 			{
-				controllers.draw(*input, injection.hook_status(), ui.debug_details);
+				controllers.draw(input_snapshot, injection.hook_status(), ui.debug_details);
 			}
 			if (ui.show_injection)
 			{

host/src/ui/app_chrome.cpp

@@ -145,7 +145,9 @@ float draw_main_menu_bar(UiState& ui, const FrameStats& stats)
 	// Right-aligned performance readout: stable FPS with the frame-time spread
 	// (min/max over the last second) so stutter is visible at a glance.
 	char perf[96];
-	std::snprintf(perf, sizeof(perf), "%.0f FPS  %.2f ms (%.2f-%.2f)", stats.fps(), stats.avg_ms(),
+	// Fixed field widths so the readout doesn't jitter/blur as values cross digit
+	// thresholds (e.g. 99 -> 100) each frame.
+	std::snprintf(perf, sizeof(perf), "%4.0f FPS  %6.2f ms (%6.2f-%6.2f)", stats.fps(), stats.avg_ms(),
 	              stats.min_ms(), stats.max_ms());
 	const float text_w = ImGui::CalcTextSize(perf).x;
 	ImGui::SameLine(ImGui::GetWindowWidth() - text_w - ImGui::GetStyle().FramePadding.x * 2.0f);