feat: Add mouse wheel support for game input passthrough

- Implement mouse wheel event handling in SDL2 backend (emu_window_sdl2)
- Add wheel event routing from GRenderWindow to input subsystem
- Add debugging logs to trace mouse wheel events through input chain
- Support mouse wheel input for mods like Ultracam when games are running (WIP)

Signed-off-by: Zephyron <zephyron@citron-emu.org>

src/citron/bootmanager.cpp

@@ -1,4 +1,5 @@
 // SPDX-FileCopyrightText: 2014 Citra Emulator Project
+// SPDX-FileCopyrightText: 2025 citron Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 #include <algorithm>
@@ -732,6 +733,7 @@ void GRenderWindow::ConstrainMouse() {
 void GRenderWindow::wheelEvent(QWheelEvent* event) {
     const int x = event->angleDelta().x();
     const int y = event->angleDelta().y();
+    LOG_DEBUG(Frontend, "GRenderWindow wheel event: x={}, y={}", x, y);
     input_subsystem->GetMouse()->MouseWheelChange(x, y);
 }
 

src/citron_cmd/emu_window/emu_window_sdl2.cpp

@@ -1,4 +1,5 @@
 // SPDX-FileCopyrightText: 2016 Citra Emulator Project
+// SPDX-FileCopyrightText: 2025 citron Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 #include <SDL.h>
@@ -77,6 +78,11 @@ void EmuWindow_SDL2::OnMouseMotion(s32 x, s32 y) {
     input_subsystem->GetMouse()->TouchMove(touch_x, touch_y);
 }
 
+void EmuWindow_SDL2::OnMouseWheel(s32 x, s32 y) {
+    input_subsystem->GetMouse()->MouseWheelChange(x, y);
+    LOG_DEBUG(Frontend, "SDL2 Mouse wheel event: x={}, y={}", x, y);
+}
+
 void EmuWindow_SDL2::OnFingerDown(float x, float y, std::size_t id) {
     input_subsystem->GetTouchScreen()->TouchPressed(x, y, id);
 }
@@ -202,6 +208,9 @@ void EmuWindow_SDL2::WaitEvent() {
             OnMouseButton(event.button.button, event.button.state, event.button.x, event.button.y);
         }
         break;
+    case SDL_MOUSEWHEEL:
+        OnMouseWheel(event.wheel.x, event.wheel.y);
+        break;
     case SDL_FINGERDOWN:
         OnFingerDown(event.tfinger.x, event.tfinger.y,
                      static_cast<std::size_t>(event.tfinger.touchId));

src/citron_cmd/emu_window/emu_window_sdl2.h

@@ -1,4 +1,5 @@
 // SPDX-FileCopyrightText: 2016 Citra Emulator Project
+// SPDX-FileCopyrightText: 2025 citron Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 #pragma once
@@ -52,6 +53,9 @@ protected:
     /// Called by WaitEvent when the mouse moves.
     void OnMouseMotion(s32 x, s32 y);
 
+    /// Called by WaitEvent when the mouse wheel is scrolled
+    void OnMouseWheel(s32 x, s32 y);
+
     /// Called by WaitEvent when a finger starts touching the touchscreen
     void OnFingerDown(float x, float y, std::size_t id);
 

src/hid_core/frontend/emulated_devices.cpp

@@ -1,4 +1,5 @@
 // SPDX-FileCopyrightText: Copyright 2021 yuzu Emulator Project
+// SPDX-FileCopyrightText: Copyright 2025 citron Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 #include <algorithm>
@@ -374,6 +375,7 @@ void EmulatedDevices::SetMouseWheel(const Common::Input::CallbackStatus& callbac
     const auto analog_value = TransformToAnalog(callback);
 
     device_status.mouse_wheel_values[index] = analog_value;
+    LOG_DEBUG(Input, "EmulatedDevices::SetMouseWheel: index={}, value={}", index, analog_value.value);
 
     if (is_configuring) {
         device_status.mouse_wheel_state = {};
@@ -455,6 +457,11 @@ AnalogStickState EmulatedDevices::GetMouseWheel() const {
     return device_status.mouse_wheel_state;
 }
 
+void EmulatedDevices::ResetMouseWheel() {
+    std::scoped_lock lock{mutex};
+    device_status.mouse_wheel_state = {};
+}
+
 void EmulatedDevices::TriggerOnChange(DeviceTriggerType type) {
     std::scoped_lock lock{callback_mutex};
     for (const auto& poller_pair : callback_list) {

src/hid_core/frontend/emulated_devices.h

@@ -135,6 +135,9 @@ public:
     /// Returns the latest mouse wheel change
     AnalogStickState GetMouseWheel() const;
 
+    /// Resets the mouse wheel state (should be called each frame)
+    void ResetMouseWheel();
+
     /**
      * Adds a callback to the list of events
      * @param update_callback InterfaceUpdateCallback that will be triggered

src/hid_core/resources/mouse/debug_mouse.cpp

@@ -1,4 +1,5 @@
 // SPDX-FileCopyrightText: Copyright 2018 yuzu Emulator Project
+// SPDX-FileCopyrightText: Copyright 2025 citron Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 #include "core/core_timing.h"
@@ -55,6 +56,9 @@ void DebugMouse::OnUpdate(const Core::Timing::CoreTiming& core_timing) {
         next_state.delta_wheel_y = mouse_wheel_state.y - last_mouse_wheel_state.y;
 
         last_mouse_wheel_state = mouse_wheel_state;
+
+        // Reset mouse wheel state after reading to ensure delta values work correctly
+        emulated_devices->ResetMouseWheel();
         next_state.button = mouse_button_state;
     }
 

src/hid_core/resources/mouse/mouse.cpp

@@ -55,6 +55,9 @@ void Mouse::OnUpdate(const Core::Timing::CoreTiming& core_timing) {
         next_state.delta_wheel_y = mouse_wheel_state.y - last_mouse_wheel_state.y;
 
         last_mouse_wheel_state = mouse_wheel_state;
+
+        // Reset mouse wheel state after reading to ensure delta values work correctly
+        emulated_devices->ResetMouseWheel();
         next_state.button = mouse_button_state;
     }
 

src/input_common/drivers/mouse.cpp

@@ -1,4 +1,5 @@
 // SPDX-FileCopyrightText: Copyright 2021 yuzu Emulator Project
+// SPDX-FileCopyrightText: Copyright 2025 citron Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 #include <thread>
@@ -235,6 +236,7 @@ void Mouse::MouseWheelChange(int x, int y) {
     wheel_position.x += x;
     wheel_position.y += y;
     last_motion_change.z += static_cast<f32>(y);
+    LOG_DEBUG(Input, "Mouse wheel change: x={}, y={}, wheel_pos=({}, {})", x, y, wheel_position.x, wheel_position.y);
     SetAxis(identifier, wheel_axis_x, static_cast<f32>(wheel_position.x));
     SetAxis(identifier, wheel_axis_y, static_cast<f32>(wheel_position.y));
 }