Added "Lean back angle" option

runtime/include/runtime_config.h

@@ -63,6 +63,7 @@ struct RuntimeUserConfig {
     std::optional<bool> vrFirstPersonHideDriver;
     std::optional<int32_t> vrFirstPersonHiddenModel;
     std::optional<std::string> vrRecenterKey;
+    std::optional<float> vrLeanBackDegrees;
     std::optional<float> audioVolume;
     std::optional<float> audioMusicVolume;
     std::optional<float> audioSoundEffectsVolume;
@@ -150,6 +151,10 @@ inline constexpr float kVrFirstPersonHeadOffsetLimit = 10.0f;
 // SDL scancode name, spelled the way SDL_GetScancodeName produces it. An
 // empty string leaves the recenter hotkey unbound, menu button only.
 inline constexpr std::string_view kVrRecenterKeyDefault = "F9";
+// Fixed pitch of the game camera for a player sitting reclined, in degrees.
+// Positive leans the camera back with you; 0 disables it entirely.
+inline constexpr float kVrLeanBackDegreesDefault = 0.0f;
+inline constexpr float kVrLeanBackDegreesLimit = 45.0f;
 
 inline std::string Trim(std::string_view text) {
     size_t begin = 0;
@@ -387,7 +392,12 @@ inline void EnsureConfigFile() {
               "# the game. Applies during an immersive race; the menu screen is\n"
               "# head-locked already. Rebindable from the F10 menu under VR. Leave\n"
               "# empty to unbind.\n"
-              "recenter_key = \"F9\"\n\n"
+              "recenter_key = \"F9\"\n"
+              "# Fixed pitch of the game camera, in degrees, for a player sitting\n"
+              "# reclined. Positive tilts the camera back with you, so 20 here cancels\n"
+              "# reclining about 20 degrees and puts the track back in front of you.\n"
+              "# 0 disables it. Changeable live from the F10 menu under VR.\n"
+              "lean_back_degrees = 0.0\n\n"
               "[audio]\n"
               "volume = 1.0\n"
               "music_volume = 1.0\n"
@@ -573,6 +583,10 @@ inline RuntimeUserConfig ParseConfigDocument(const toml::value& document) {
     if (auto value = FindConfigValue<std::string>(document, "vr", "recenter_key")) {
         config.vrRecenterKey = *value;
     }
+    if (auto value = FindConfigFloat(document, "vr", "lean_back_degrees");
+        value && *value >= -kVrLeanBackDegreesLimit && *value <= kVrLeanBackDegreesLimit) {
+        config.vrLeanBackDegrees = static_cast<float>(*value);
+    }
     if (auto value = FindConfigInt(document, "vr", "first_person_hidden_model");
         value && *value >= -1 && *value <= 31) {
         config.vrFirstPersonHiddenModel = static_cast<int32_t>(*value);
@@ -853,6 +867,14 @@ inline bool SetVrRecenterKey(std::string value) {
     return WriteSetting("vr", "recenter_key", FormatString(value));
 }
 
+inline bool SetVrLeanBackDegrees(float value) {
+    value = std::clamp(value, -kVrLeanBackDegreesLimit, kVrLeanBackDegreesLimit);
+    Mutable().vrLeanBackDegrees = value;
+    std::ostringstream formatted;
+    formatted << value;
+    return WriteSetting("vr", "lean_back_degrees", formatted.str());
+}
+
 inline bool SetVrFirstPersonHideDriver(bool value) {
     Mutable().vrFirstPersonHideDriver = value;
     return WriteSetting("vr", "first_person_hide_driver", value ? "true" : "false");
@@ -1149,6 +1171,11 @@ inline std::string VrRecenterKey(std::string fallback = std::string(kVrRecenterK
     return Get().vrRecenterKey.value_or(std::move(fallback));
 }
 
+inline float VrLeanBackDegrees(float fallback = kVrLeanBackDegreesDefault) {
+    return std::clamp(Get().vrLeanBackDegrees.value_or(fallback),
+                      -kVrLeanBackDegreesLimit, kVrLeanBackDegreesLimit);
+}
+
 inline bool VrFirstPersonHideDriver(bool fallback = kVrFirstPersonHideDriverDefault) {
     return Get().vrFirstPersonHideDriver.value_or(fallback);
 }

runtime/include/vr/openxr_integration.h

@@ -44,4 +44,12 @@ std::string OpenXRLastError();
 // immersive race, where the head-locked menu screen has no origin to recenter.
 void OpenXRRequestRecenter() noexcept;
 
+// Sets a fixed pitch of the game camera for a player sitting reclined, in
+// degrees, clamped to RuntimeConfigFile::kVrLeanBackDegreesLimit. Positive
+// tilts the camera back with the player, so an angle matching how far they are
+// reclined puts the track back in front of them. 0 applies no pitch at all.
+// Applies to the immersive race view only; callable from any thread and read
+// once per published frame.
+void OpenXRSetLeanBackDegrees(float degrees) noexcept;
+
 } // namespace mkw::vr

runtime/src/settings_overlay.cpp

@@ -121,6 +121,7 @@ SDL_Scancode g_vrRecenterScancode = [] {
                         : SDL_GetScancodeFromName(name.c_str());
 }();
 bool g_vrRecenterRebinding = false;
+float g_vrLeanBackDegrees = RuntimeConfigFile::VrLeanBackDegrees();
 uint32_t g_disabledPostProcessingPaths = RuntimeConfigFile::DisabledPostProcessingPaths(0);
 std::array<int32_t, PAD_MAX_CONTROLLERS> g_configuredControllerIndices = [] {
     std::array<int32_t, PAD_MAX_CONTROLLERS> indices{};
@@ -909,6 +910,20 @@ void DrawVrSettings() {
             ImGui::SetTooltip("Click to rebind. Esc cancels, Backspace unbinds.");
         }
     }
+    if (ImGui::SliderFloat("Lean back angle (deg)", &g_vrLeanBackDegrees,
+                           -RuntimeConfigFile::kVrLeanBackDegreesLimit,
+                           RuntimeConfigFile::kVrLeanBackDegreesLimit, "%.1f")) {
+        mkw::vr::OpenXRSetLeanBackDegrees(g_vrLeanBackDegrees);
+        RuntimeConfigFile::SetVrLeanBackDegrees(g_vrLeanBackDegrees);
+    }
+    if (ImGui::IsItemHovered()) {
+        ImGui::SetTooltip(
+            "Tilts the game camera back with you when you play reclined, so set it to "
+            "roughly how far back your seat is and the track comes back in front of you "
+            "instead of above. 0 applies no tilt. Unlike recentering, this deliberately "
+            "does pitch the view, and looking sideways while it is set will roll the "
+            "horizon the way a real recline would.");
+    }
     ImGui::Separator();
     ImGui::Text("VR camera");
     if (ImGui::Checkbox("First-person camera", &g_vrFirstPerson)) {

runtime/src/vr/openxr_integration.cpp

@@ -37,6 +37,8 @@
 namespace mkw::vr {
 namespace {
 
+inline constexpr float kDegreesToRadians = 0.01745329252f;
+
 void ConfigurePolicy(bool enabled) noexcept {
     MkwVRPolicyReset();
     MkwVRPolicyConfig config{};
@@ -78,6 +80,15 @@ Quaternion Conjugate(Quaternion value) noexcept {
     return {-value.x, -value.y, -value.z, value.w};
 }
 
+Quaternion Multiply(const Quaternion& left, const Quaternion& right) noexcept {
+    return Normalize({
+        left.w * right.x + left.x * right.w + left.y * right.z - left.z * right.y,
+        left.w * right.y - left.x * right.z + left.y * right.w + left.z * right.x,
+        left.w * right.z + left.x * right.y - left.y * right.x + left.z * right.w,
+        left.w * right.w - left.x * right.x - left.y * right.y - left.z * right.z,
+    });
+}
+
 std::array<float, 3> Rotate(const Quaternion& q, const std::array<float, 3>& value) noexcept {
     // Expanded q * [v,0] * conjugate(q), avoiding two temporary normalizations.
     const float tx = 2.0f * (q.y * value[2] - q.z * value[1]);
@@ -155,13 +166,26 @@ void ProjectionFromFov(const XrFovf& fov, float output[16]) noexcept {
 // leaves the game's horizon level and its forward fixed to the reference space.
 // Composing a latched head orientation in here instead would bake that instant's
 // pitch and roll into the neutral and tilt the horizon for the rest of the session.
+//
+// lean_back_radians is the one deliberate exception: a fixed pitch of the game
+// camera about the reference space's right axis, for a player sitting reclined.
+// It multiplies in on the right, so it turns the world before the head rotation
+// rather than after it, which is what makes it cancel a reclined head exactly
+// and, when you then look sideways, roll the view the way a real recline would.
 void ViewFromBase(const XrPosef& eye_pose, const std::array<float, 3>& base_position,
-                  bool position_valid, float units_per_meter, float output[12]) noexcept {
+                  bool position_valid, float units_per_meter, float lean_back_radians,
+                  float output[12]) noexcept {
     const Quaternion eye = Normalize({eye_pose.orientation.x, eye_pose.orientation.y,
                                       eye_pose.orientation.z, eye_pose.orientation.w});
     const Quaternion inverse_eye = Conjugate(eye);
     float rotation[9];
-    RotationMatrix(inverse_eye, rotation);
+    if (lean_back_radians == 0.0f) {
+        RotationMatrix(inverse_eye, rotation);
+    } else {
+        const float half_angle = 0.5f * lean_back_radians;
+        const Quaternion lean{std::sin(half_angle), 0.0f, 0.0f, std::cos(half_angle)};
+        RotationMatrix(Multiply(inverse_eye, lean), rotation);
+    }
 
     std::array<float, 3> translation{};
     if (position_valid) {
@@ -326,6 +350,13 @@ public:
         recenter_requested_.store(true, std::memory_order_release);
     }
 
+    void SetLeanBackDegrees(float degrees) noexcept {
+        lean_back_degrees_.store(
+            std::clamp(degrees, -RuntimeConfigFile::kVrLeanBackDegreesLimit,
+                       RuntimeConfigFile::kVrLeanBackDegreesLimit),
+            std::memory_order_relaxed);
+    }
+
     void ServiceProducerFrameBoundary() noexcept {
         if (teardown_requested_.load(std::memory_order_acquire)) {
             Shutdown();
@@ -596,12 +627,16 @@ private:
             base_position_valid_ = true;
         }
         last_immersive_ = true;
+        // Read once so both eyes are built from the same angle even if the
+        // settings slider moves between them.
+        const float lean_back_radians =
+            lean_back_degrees_.load(std::memory_order_relaxed) * kDegreesToRadians;
         for (uint32_t eye = 0; eye < kOpenXREyeCount; ++eye) {
             ProjectionFromFov(source.xr_frame.views[eye].fov,
                               destination.eyes[eye].projection);
             ViewFromBase(source.xr_frame.views[eye].pose, base_position_,
-                         position_valid && base_position_valid_,
+                         position_valid && base_position_valid_, units_per_meter,
-                         units_per_meter, destination.eyes[eye].viewFromCenter);
+                         lean_back_radians, destination.eyes[eye].viewFromCenter);
         }
     }
 
@@ -644,6 +679,7 @@ private:
     std::atomic_bool running_{false};
     std::atomic_bool teardown_requested_{false};
     std::atomic_bool recenter_requested_{false};
+    std::atomic<float> lean_back_degrees_{RuntimeConfigFile::VrLeanBackDegrees()};
     std::atomic<PublishedFrame*> published_{nullptr};
     PublishedFrame published_frame_{};
     std::mutex published_mutex_;
@@ -722,6 +758,14 @@ void OpenXRRequestRecenter() noexcept {
 #endif
 }
 
+void OpenXRSetLeanBackDegrees(float degrees) noexcept {
+#if defined(MKW_ENABLE_OPENXR) && defined(_WIN32)
+    OpenXRIntegration::Get().SetLeanBackDegrees(degrees);
+#else
+    (void)degrees;
+#endif
+}
+
 std::string OpenXRLastError() {
 #if !defined(MKW_ENABLE_OPENXR)
     return "this build was compiled without OpenXR support";