Added Yaw only / Yaw + Pitch / Full rotation options to first-person

runtime/include/runtime_config.h

@@ -62,6 +62,7 @@ struct RuntimeUserConfig {
     std::optional<float> vrFirstPersonHeadRightMeters;
     std::optional<bool> vrFirstPersonHideDriver;
     std::optional<int32_t> vrFirstPersonHiddenModel;
+    std::optional<std::string> vrFirstPersonRotation;
     std::optional<std::string> vrRecenterKey;
     std::optional<float> vrLeanBackDegrees;
     std::optional<float> audioVolume;
@@ -148,6 +149,12 @@ inline constexpr float kVrFirstPersonHeadRightDefault = 0.0f;
 inline constexpr bool kVrFirstPersonHideDriverDefault = true;
 inline constexpr int32_t kVrFirstPersonHiddenModelDefault = 0;
 inline constexpr float kVrFirstPersonHeadOffsetLimit = 10.0f;
+// "yaw", "yaw_pitch" or "full", matching FirstPersonRotation.
+inline constexpr const char* kVrFirstPersonRotationDefault = "yaw";
+
+inline bool IsSupportedVrFirstPersonRotation(std::string_view value) {
+    return value == "yaw" || value == "yaw_pitch" || value == "full";
+}
 // 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";
@@ -385,6 +392,10 @@ inline void EnsureConfigFile() {
               "# 0 is the driver, which is the usual choice. -1 hides every\n"
               "# model of your kart, the vehicle included.\n"
               "first_person_hidden_model = 0\n"
+              "# Where the view's orientation comes from: \"yaw\" levels the\n"
+              "# horizon, \"yaw_pitch\" adds the kart's climb but no roll, and\n"
+              "# \"full\" takes the kart's whole orientation so the view banks.\n"
+              "first_person_rotation = \"yaw\"\n\n"
               "# Keyboard shortcut that recenters the VR view, naming the key the\n"
               "# way SDL does (F9, Home, Keypad 5, ...). It moves the race view to\n"
               "# where you are sitting now and brings the menu screen back upright in\n"
@@ -587,6 +598,10 @@ inline RuntimeUserConfig ParseConfigDocument(const toml::value& document) {
         value && *value >= -kVrLeanBackDegreesLimit && *value <= kVrLeanBackDegreesLimit) {
         config.vrLeanBackDegrees = static_cast<float>(*value);
     }
+    if (auto value = FindConfigValue<std::string>(document, "vr", "first_person_rotation");
+        value && IsSupportedVrFirstPersonRotation(*value)) {
+        config.vrFirstPersonRotation = *value;
+    }
     if (auto value = FindConfigInt(document, "vr", "first_person_hidden_model");
         value && *value >= -1 && *value <= 31) {
         config.vrFirstPersonHiddenModel = static_cast<int32_t>(*value);
@@ -880,6 +895,14 @@ inline bool SetVrFirstPersonHideDriver(bool value) {
     return WriteSetting("vr", "first_person_hide_driver", value ? "true" : "false");
 }
 
+inline bool SetVrFirstPersonRotation(std::string value) {
+    if (!IsSupportedVrFirstPersonRotation(value)) {
+        return false;
+    }
+    Mutable().vrFirstPersonRotation = value;
+    return WriteSetting("vr", "first_person_rotation", FormatString(value));
+}
+
 inline bool SetVrFirstPersonHiddenModel(int32_t value) {
     value = std::clamp(value, -1, 31);
     Mutable().vrFirstPersonHiddenModel = value;
@@ -1180,6 +1203,11 @@ inline bool VrFirstPersonHideDriver(bool fallback = kVrFirstPersonHideDriverDefa
     return Get().vrFirstPersonHideDriver.value_or(fallback);
 }
 
+inline std::string VrFirstPersonRotation(std::string fallback = kVrFirstPersonRotationDefault) {
+    const auto& value = Get().vrFirstPersonRotation;
+    return value && IsSupportedVrFirstPersonRotation(*value) ? *value : std::move(fallback);
+}
+
 inline int32_t VrFirstPersonHiddenModel(int32_t fallback = kVrFirstPersonHiddenModelDefault) {
     return std::clamp(Get().vrFirstPersonHiddenModel.value_or(fallback), -1, 31);
 }

runtime/include/vr/mkw_vr_first_person.h

@@ -27,6 +27,19 @@ struct FirstPersonHeadOffsets {
     float forward = 0.0f;
 };
 
+// Where the anchored camera's orientation comes from, mirroring DolphinXR's
+// camera-anchor modes. The headset always adds free look on top of whichever
+// is chosen; this only decides the frame it looks around from.
+enum class FirstPersonRotation : uint8_t {
+    // The horizon is kept level and only a heading is taken. Comfort default.
+    YawOnly,
+    // The kart's heading and its climb, with roll dropped: slopes and wheelies
+    // tip the view, but a banked corner never rolls the horizon.
+    YawPitch,
+    // The kart's whole orientation, so the view banks and pitches with it.
+    Full,
+};
+
 // The camera relocation published to Aurora for one guest frame: a transform
 // from the game's recorded view space into the space the headset renders from.
 struct FirstPersonAnchor {
@@ -87,6 +100,32 @@ inline bool Normalize(Vec3& value) noexcept {
     return true;
 }
 
+// out = matrix's 3x3 * (x, y, z). Directions ignore the translation column.
+inline Vec3 TransformDirection(const Mtx34& matrix, const Vec3& v) noexcept {
+    return {
+        matrix[0] * v.x + matrix[1] * v.y + matrix[2] * v.z,
+        matrix[4] * v.x + matrix[5] * v.y + matrix[6] * v.z,
+        matrix[8] * v.x + matrix[9] * v.y + matrix[10] * v.z,
+    };
+}
+
+// Fills the three basis rows from a forward and an up that need not be exactly
+// perpendicular, in the -Z-forward convention view space uses.
+inline bool BasisFromForwardUp(const Vec3& forward_in, const Vec3& up_in, Vec3 rows[3]) noexcept {
+    Vec3 forward = forward_in;
+    if (!Normalize(forward)) {
+        return false;
+    }
+    Vec3 right = Cross(forward, up_in);
+    if (!Normalize(right)) {
+        return false;
+    }
+    rows[0] = right;
+    rows[1] = Cross(right, forward);
+    rows[2] = {-forward.x, -forward.y, -forward.z};
+    return true;
+}
+
 // out = matrix * (x, y, z, 1)
 inline Vec3 TransformPoint(const Mtx34& matrix, float x, float y, float z) noexcept {
     return {
@@ -102,14 +141,12 @@ inline Vec3 TransformPoint(const Mtx34& matrix, float x, float y, float z) noexc
 // the kart's pose (kart-local -> world), and head offsets already converted to
 // world units.
 //
-// The translation moves the camera onto the head. With level_horizon the
-// rotation keeps the recorded camera's heading but drops its pitch and roll, so
-// the headset owns pitch and roll outright; without it the recorded camera's
-// orientation is kept whole and only the eye moves. Returns false and leaves
-// `out` untouched when the inputs cannot produce an orthonormal frame.
+// The translation always moves the camera onto the head; `rotation` decides the
+// frame it looks around from. Returns false and leaves `out` untouched when the
+// inputs cannot produce an orthonormal frame.
 inline bool ComputeFirstPersonAnchor(const Mtx34& view_from_world, const Mtx34& kart_from_local,
                                      float head_right_units, float head_up_units,
-                                     float head_forward_units, bool level_horizon,
+                                     float head_forward_units, FirstPersonRotation rotation,
                                      Mtx34& out) noexcept {
     using namespace detail;
     if (!IsFiniteMtx34(view_from_world) || !IsFiniteMtx34(kart_from_local)) {
@@ -124,39 +161,55 @@ inline bool ComputeFirstPersonAnchor(const Mtx34& view_from_world, const Mtx34&
 
     // Rows of the anchor's rotation. Identity keeps the recorded camera's own
     // orientation and moves the eye only.
+    // Every mode is the same construction from a forward and an up; they differ
+    // only in which pair they take. Pairing a forward with world up is what
+    // removes roll, since the resulting right axis is then always horizontal.
     Vec3 rows[3]{{1.0f, 0.0f, 0.0f}, {0.0f, 1.0f, 0.0f}, {0.0f, 0.0f, 1.0f}};
-    if (level_horizon) {
-        // World +Y in view coordinates: the column of the view rotation that
-        // the world up axis selects.
-        Vec3 up{view_from_world[1], view_from_world[5], view_from_world[9]};
-        if (!Normalize(up)) {
+    // World +Y in view coordinates: the column of the view rotation that the
+    // world up axis selects.
+    Vec3 world_up{view_from_world[1], view_from_world[5], view_from_world[9]};
+    const bool world_up_valid = Normalize(world_up);
+    // Columns 2 and 1 of the kart pose are its forward and up. The pose may
+    // carry scale, so the pair is re-orthonormalized rather than trusted.
+    const Vec3 kart_forward = TransformDirection(
+        view_from_world, {kart_from_local[2], kart_from_local[6], kart_from_local[10]});
+    const Vec3 kart_up = TransformDirection(
+        view_from_world, {kart_from_local[1], kart_from_local[5], kart_from_local[9]});
+
+    if (rotation == FirstPersonRotation::YawOnly) {
+        if (!world_up_valid) {
             return false;
         }
         // Level the recorded camera's forward (-Z in its own space) onto the
         // horizon plane. Looking near-straight up or down leaves nothing to
         // project, so recover the heading from the camera's up axis instead.
         const Vec3 camera_forward{0.0f, 0.0f, -1.0f};
-        float along = Dot(camera_forward, up);
-        Vec3 forward{camera_forward.x - up.x * along, camera_forward.y - up.y * along,
-                     camera_forward.z - up.z * along};
+        float along = Dot(camera_forward, world_up);
+        Vec3 forward{camera_forward.x - world_up.x * along, camera_forward.y - world_up.y * along,
+                     camera_forward.z - world_up.z * along};
         if (!Normalize(forward)) {
             const Vec3 camera_up{0.0f, 1.0f, 0.0f};
-            along = Dot(camera_up, up);
-            forward = {camera_up.x - up.x * along, camera_up.y - up.y * along,
-                       camera_up.z - up.z * along};
+            along = Dot(camera_up, world_up);
+            forward = {camera_up.x - world_up.x * along, camera_up.y - world_up.y * along,
+                       camera_up.z - world_up.z * along};
             if (!Normalize(forward)) {
                 return false;
             }
         }
-        Vec3 right = Cross(forward, up);
-        if (!Normalize(right)) {
+        if (!BasisFromForwardUp(forward, world_up, rows)) {
             return false;
         }
-        // Re-derive up from the orthonormalized pair so a slightly non-rigid
-        // view matrix cannot leave a skewed frame behind.
-        rows[0] = right;
-        rows[1] = Cross(right, forward);
-        rows[2] = {-forward.x, -forward.y, -forward.z};
+    } else if (rotation == FirstPersonRotation::YawPitch) {
+        // The kart's heading and climb, levelled against world up so no roll
+        // survives. Pointing straight up or down leaves nothing to level
+        // against, so that frame falls back to the kart's own up.
+        if (!world_up_valid || !BasisFromForwardUp(kart_forward, world_up, rows)) {
+            if (!BasisFromForwardUp(kart_forward, kart_up, rows)) {
+                return false;
+            }
+        }
+    } else if (!BasisFromForwardUp(kart_forward, kart_up, rows)) {
+        return false;
     }
 
     Mtx34 anchor{};
@@ -181,7 +234,7 @@ inline bool ComputeFirstPersonAnchor(const Mtx34& view_from_world, const Mtx34&
 // Enables anchor computation and sets the head offsets and world scale used to
 // convert them. Called whenever the configuration or the F10 toggle changes.
 void MkwVRFirstPersonConfigure(bool enabled, const FirstPersonHeadOffsets& offsets,
-                               float units_per_meter) noexcept;
+                               float units_per_meter, FirstPersonRotation rotation) noexcept;
 
 // While the anchor is driving the view the player's own models can be removed,
 // since the driver otherwise sits exactly where the eyes are. This uses the

runtime/src/settings_overlay.cpp

@@ -113,6 +113,16 @@ float g_vrFirstPersonHeadForward = RuntimeConfigFile::VrFirstPersonHeadForwardMe
 float g_vrFirstPersonHeadRight = RuntimeConfigFile::VrFirstPersonHeadRightMeters();
 bool g_vrFirstPersonHideDriver = RuntimeConfigFile::VrFirstPersonHideDriver();
 int g_vrFirstPersonHiddenModel = RuntimeConfigFile::VrFirstPersonHiddenModel();
+constexpr std::array<const char*, 3> kVrFirstPersonRotationNames{"yaw", "yaw_pitch", "full"};
+int g_vrFirstPersonRotation = [] {
+    const std::string mode = RuntimeConfigFile::VrFirstPersonRotation();
+    for (size_t i = 0; i < kVrFirstPersonRotationNames.size(); ++i) {
+        if (mode == kVrFirstPersonRotationNames[i]) {
+            return static_cast<int>(i);
+        }
+    }
+    return 0;
+}();
 // SDL_SCANCODE_UNKNOWN means unbound, which is also what an unrecognised
 // name in the config file resolves to rather than silently picking a key.
 SDL_Scancode g_vrRecenterScancode = [] {
@@ -967,6 +977,21 @@ void DrawVrSettings() {
     ImGui::PushTextWrapPos(ImGui::GetCursorPosX() + 380.0f);
     ImGui::TextDisabled("Where the head sits in the kart's own frame.");
     ImGui::PopTextWrapPos();
+    constexpr std::array<const char*, 3> kRotationLabels{"Yaw only", "Yaw + Pitch", "Full rotation"};
+    if (ImGui::Combo("View rotation", &g_vrFirstPersonRotation, kRotationLabels.data(),
+                     static_cast<int>(kRotationLabels.size()))) {
+        RuntimeConfigFile::SetVrFirstPersonRotation(
+            kVrFirstPersonRotationNames[static_cast<size_t>(g_vrFirstPersonRotation)]);
+        mkw::vr::MkwVRFirstPersonApplyConfiguredSettings();
+    }
+    if (ImGui::IsItemHovered()) {
+        ImGui::SetTooltip(
+            "Where the view's orientation comes from. Yaw only keeps the horizon level "
+            "and is the comfortable choice. Yaw + Pitch adds the kart's climb, so slopes "
+            "and wheelies tip the view without ever rolling it. Full rotation takes the "
+            "kart's whole orientation, banking included. The headset always adds free look "
+            "on top.");
+    }
     // Two presentations of one setting: which models go, or none at all.
     // Ticking either replaces the other, and unticking both shows everything.
     const auto applyHiding = [](bool enabled, int model) {
@@ -1002,6 +1027,9 @@ void DrawVrSettings() {
         g_vrFirstPersonHeadRight = RuntimeConfigFile::kVrFirstPersonHeadRightDefault;
         g_vrFirstPersonHideDriver = RuntimeConfigFile::kVrFirstPersonHideDriverDefault;
         g_vrFirstPersonHiddenModel = RuntimeConfigFile::kVrFirstPersonHiddenModelDefault;
+        g_vrFirstPersonRotation = 0;
+        RuntimeConfigFile::SetVrFirstPersonRotation(
+            RuntimeConfigFile::kVrFirstPersonRotationDefault);
         RuntimeConfigFile::SetVrFirstPersonUnitsPerMeter(g_vrFirstPersonUnitsPerMeter);
         RuntimeConfigFile::SetVrFirstPersonHeadUpMeters(g_vrFirstPersonHeadUp);
         RuntimeConfigFile::SetVrFirstPersonHeadForwardMeters(g_vrFirstPersonHeadForward);

runtime/src/vr/mkw_vr_first_person.cpp

@@ -8,6 +8,7 @@
 #include "vr/mkw_vr_policy.h"
 
 #include <mutex>
+#include <string>
 
 extern "C" void func_805A6C58(CpuContext* context);
 extern "C" void func_8056A470(CpuContext* context);
@@ -236,6 +237,7 @@ struct FirstPersonState {
     bool enabled = false;
     FirstPersonHeadOffsets offsets{};
     float units_per_meter = RuntimeConfigFile::kVrFirstPersonUnitsPerMeterDefault;
+    FirstPersonRotation rotation = FirstPersonRotation::YawOnly;
 
     uint32_t camera_address = 0;
     // Armed by the draw boundary, consumed by the frame seal.
@@ -494,10 +496,11 @@ void LogAnchorLocked(uint64_t frame, const Mtx34& anchor, const Mtx34& view_from
 } // namespace
 
 void MkwVRFirstPersonConfigure(bool enabled, const FirstPersonHeadOffsets& offsets,
-                               float units_per_meter) noexcept {
+                               float units_per_meter, FirstPersonRotation rotation) noexcept {
     std::lock_guard lock(g_mutex);
     g_state.enabled = enabled;
     g_state.offsets = offsets;
+    g_state.rotation = rotation;
     if (detail::IsFiniteFloat(&units_per_meter) && units_per_meter > 0.0f) {
         g_state.units_per_meter = units_per_meter;
     }
@@ -514,7 +517,12 @@ void MkwVRFirstPersonApplyConfiguredSettings() noexcept {
         RuntimeConfigFile::VrFirstPersonHeadUpMeters(),
         RuntimeConfigFile::VrFirstPersonHeadForwardMeters(),
     };
-    MkwVRFirstPersonConfigure(RuntimeConfigFile::VrFirstPerson(false), offsets, units_per_meter);
+    const std::string mode = RuntimeConfigFile::VrFirstPersonRotation();
+    const FirstPersonRotation rotation = mode == "full" ? FirstPersonRotation::Full
+                                         : mode == "yaw_pitch" ? FirstPersonRotation::YawPitch
+                                                               : FirstPersonRotation::YawOnly;
+    MkwVRFirstPersonConfigure(RuntimeConfigFile::VrFirstPerson(false), offsets, units_per_meter,
+                              rotation);
     MkwVRPolicySetFirstPersonUnitsPerMeter(units_per_meter);
     {
         // Same lock the guest thread applies these under.
@@ -589,7 +597,7 @@ void MkwVRFirstPersonCommit() noexcept {
                                          g_state.offsets.right * g_state.units_per_meter,
                                          g_state.offsets.up * g_state.units_per_meter,
                                          g_state.offsets.forward * g_state.units_per_meter,
-                                         /*level_horizon=*/true, anchor)) {
+                                         g_state.rotation, anchor)) {
         failed_step = "anchor math (degenerate camera or kart frame)";
     }
 

runtime/tests/vr_first_person_tests.cpp

@@ -15,6 +15,7 @@ namespace {
 
 using mkw::vr::ComputeFirstPersonAnchor;
 using mkw::vr::kIdentityMtx34;
+using mkw::vr::FirstPersonRotation;
 using mkw::vr::Mtx34;
 
 int g_failures = 0;
@@ -77,20 +78,23 @@ Mtx34 KartAt(float x, float y, float z) {
 void TestNeutralInputsProduceIdentity() {
     Mtx34 anchor{};
     Check(ComputeFirstPersonAnchor(kIdentityMtx34, kIdentityMtx34, 0.0f, 0.0f, 0.0f,
-                                   /*level_horizon=*/true, anchor),
+                                   FirstPersonRotation::YawOnly, anchor),
           "a camera already at the head must produce an anchor");
     for (size_t i = 0; i < anchor.size(); ++i) {
         CheckNear(anchor[i], kIdentityMtx34[i], "neutral inputs must produce the identity anchor");
     }
 }
 
-void TestUnlevelledAnchorIsPureTranslation() {
+void TestLevelCameraGivesPureTranslation() {
     // Camera 5 m behind and 2 m above the origin, kart at the origin, head 1 m up.
+    // A camera that is already level needs no rotation, so the anchor reduces to
+    // the translation and the head-placement math is visible on its own.
     const Mtx34 view = LevelViewAt(0.0f, 2.0f, 5.0f);
     const Mtx34 kart = KartAt(0.0f, 0.0f, 0.0f);
     Mtx34 anchor{};
-    Check(ComputeFirstPersonAnchor(view, kart, 0.0f, 1.0f, 0.0f, /*level_horizon=*/false, anchor),
-          "an unlevelled anchor must be computable");
+    Check(ComputeFirstPersonAnchor(view, kart, 0.0f, 1.0f, 0.0f, FirstPersonRotation::YawOnly,
+                                   anchor),
+          "a level camera must produce an anchor");
 
     // The head sits at (0, -1, -5) in view space, so the anchor's translation
     // is its negation.
@@ -113,7 +117,7 @@ void TestLevellingRemovesCameraPitch() {
     const Mtx34 view = PitchedViewAt(0.0f, 2.0f, 5.0f, pitch);
     const Mtx34 kart = KartAt(0.0f, 0.0f, 0.0f);
     Mtx34 anchor{};
-    Check(ComputeFirstPersonAnchor(view, kart, 0.0f, 1.0f, 0.0f, /*level_horizon=*/true, anchor),
+    Check(ComputeFirstPersonAnchor(view, kart, 0.0f, 1.0f, 0.0f, FirstPersonRotation::YawOnly, anchor),
           "a pitched camera must still produce an anchor");
 
     // The anchored camera's axes, expressed in world space: rows of A_rot times
@@ -157,7 +161,7 @@ void TestAnchorRotationStaysOrthonormal() {
         const Mtx34 view = PitchedViewAt(3.0f, 12.0f, -7.0f, pitch);
         Mtx34 anchor{};
         Check(ComputeFirstPersonAnchor(view, KartAt(3.0f, 0.0f, -20.0f), 0.1f, 1.0f, 0.2f,
-                                       /*level_horizon=*/true, anchor),
+                                       FirstPersonRotation::YawOnly, anchor),
               "every camera pitch must produce an anchor");
         for (size_t row = 0; row < 3; ++row) {
             for (size_t other = row; other < 3; ++other) {
@@ -177,7 +181,7 @@ void TestNonFiniteInputIsRejected() {
     broken[3] = std::numeric_limits<float>::infinity();
     Mtx34 anchor = kIdentityMtx34;
     anchor[3] = 1234.0f;
-    Check(!ComputeFirstPersonAnchor(broken, kIdentityMtx34, 0.0f, 1.0f, 0.0f, true, anchor),
+    Check(!ComputeFirstPersonAnchor(broken, kIdentityMtx34, 0.0f, 1.0f, 0.0f, FirstPersonRotation::YawOnly, anchor),
           "a non-finite view matrix must be rejected");
     CheckNear(anchor[3], 1234.0f, "a rejected anchor must leave the output untouched");
 }
@@ -186,17 +190,130 @@ void TestDegenerateKartPoseIsRejected() {
     Mtx34 collapsed{};
     Mtx34 anchor{};
     // A zeroed view matrix has no world up to level against.
-    Check(!ComputeFirstPersonAnchor(collapsed, kIdentityMtx34, 0.0f, 1.0f, 0.0f, true, anchor),
+    Check(!ComputeFirstPersonAnchor(collapsed, kIdentityMtx34, 0.0f, 1.0f, 0.0f, FirstPersonRotation::YawOnly, anchor),
           "a collapsed view matrix must be rejected");
 }
 
+// A kart pitched up by `pitch` and rolled by `roll`, heading toward -Z so it
+// points away from a level camera. Only columns 1 and 2 are read by the anchor.
+Mtx34 KartPitchedAndRolled(float pitch, float roll) {
+    const float cp = std::cos(pitch), sp = std::sin(pitch);
+    const float cr = std::cos(roll), sr = std::sin(roll);
+    const float forward[3]{0.0f, sp, -cp};
+    const float upUnrolled[3]{0.0f, cp, sp};
+    const float rightUnrolled[3]{1.0f, 0.0f, 0.0f};
+    Mtx34 pose{};
+    for (size_t row = 0; row < 3; ++row) {
+        pose[row * 4 + 1] = -rightUnrolled[row] * sr + upUnrolled[row] * cr;
+        pose[row * 4 + 2] = forward[row];
+    }
+    return pose;
+}
+
+void TestYawPitchKeepsClimbAndDropsRoll() {
+    const float pitch = 0.4f, roll = 0.5f;
+    const Mtx34 view = LevelViewAt(0.0f, 2.0f, 5.0f);
+    Mtx34 anchor{};
+    Check(ComputeFirstPersonAnchor(view, KartPitchedAndRolled(pitch, roll), 0.0f, 0.0f, 0.0f,
+                                   FirstPersonRotation::YawPitch, anchor),
+          "yaw+pitch must be computable");
+
+    // The climb survives: the anchor's forward is the kart's forward.
+    CheckNear(-anchor[9], std::sin(pitch), "yaw+pitch keeps the kart's climb (y)");
+    CheckNear(-anchor[10], -std::cos(pitch), "yaw+pitch keeps the kart's heading (z)");
+    // The roll does not: the right axis stays horizontal.
+    CheckNear(anchor[1], 0.0f, "yaw+pitch leaves the right axis horizontal");
+
+    // Full rotation on the same kart does keep the roll, so the two differ.
+    Mtx34 full{};
+    Check(ComputeFirstPersonAnchor(view, KartPitchedAndRolled(pitch, roll), 0.0f, 0.0f, 0.0f,
+                                   FirstPersonRotation::Full, full),
+          "full rotation must be computable");
+    Check(std::fabs(full[1]) > 0.1f, "full rotation keeps the roll yaw+pitch drops");
+
+    for (size_t row = 0; row < 3; ++row) {
+        for (size_t other = row; other < 3; ++other) {
+            float dot = 0.0f;
+            for (size_t axis = 0; axis < 3; ++axis) {
+                dot += anchor[row * 4 + axis] * anchor[other * 4 + axis];
+            }
+            CheckNear(dot, row == other ? 1.0f : 0.0f, "yaw+pitch stays orthonormal");
+        }
+    }
+}
+
+// A kart yawed by `yaw` and rolled by `roll`, as a kart-local -> world pose.
+Mtx34 KartOriented(float yaw, float roll) {
+    const float cy = std::cos(yaw), sy = std::sin(yaw);
+    const float cr = std::cos(roll), sr = std::sin(roll);
+    // Columns are the kart's right, up and forward axes in world space.
+    const float right[3]{cy * cr, sr, -sy * cr};
+    const float up[3]{-cy * sr, cr, sy * sr};
+    const float forward[3]{sy, 0.0f, cy};
+    Mtx34 pose{};
+    for (size_t row = 0; row < 3; ++row) {
+        pose[row * 4 + 0] = right[row];
+        pose[row * 4 + 1] = up[row];
+        pose[row * 4 + 2] = forward[row];
+    }
+    return pose;
+}
+
+void TestFullRotationFollowsTheKart() {
+    // A level camera, and a kart yawed and rolled away from it. Full rotation
+    // must adopt the kart's frame, not the camera's.
+    const Mtx34 view = LevelViewAt(0.0f, 2.0f, 5.0f);
+    const float yaw = 0.6f, roll = 0.4f;
+    Mtx34 anchor{};
+    Check(ComputeFirstPersonAnchor(view, KartOriented(yaw, roll), 0.0f, 0.0f, 0.0f,
+                                   FirstPersonRotation::Full, anchor),
+          "full rotation must be computable");
+
+    // With an identity view rotation the anchor rows are the kart's axes
+    // directly, so the third row is the kart's backward axis.
+    CheckNear(anchor[8], -std::sin(yaw), "full rotation takes the kart's heading (x)");
+    CheckNear(anchor[10], -std::cos(yaw), "full rotation takes the kart's heading (z)");
+    // Roll survives: the anchor's up is the kart's up, not world up.
+    CheckNear(anchor[5], std::cos(roll), "full rotation keeps the kart's roll");
+
+    for (size_t row = 0; row < 3; ++row) {
+        for (size_t other = row; other < 3; ++other) {
+            float dot = 0.0f;
+            for (size_t axis = 0; axis < 3; ++axis) {
+                dot += anchor[row * 4 + axis] * anchor[other * 4 + axis];
+            }
+            CheckNear(dot, row == other ? 1.0f : 0.0f, "full rotation stays orthonormal");
+        }
+    }
+}
+
+void TestYawOnlyIgnoresKartRoll() {
+    // The same rolled kart, but yaw-only must leave the horizon level.
+    const Mtx34 view = LevelViewAt(0.0f, 2.0f, 5.0f);
+    Mtx34 rolled{};
+    Mtx34 upright{};
+    Check(ComputeFirstPersonAnchor(view, KartOriented(0.6f, 0.4f), 0.0f, 0.0f, 0.0f,
+                                   FirstPersonRotation::YawOnly, rolled),
+          "yaw-only must be computable for a rolled kart");
+    Check(ComputeFirstPersonAnchor(view, KartOriented(0.6f, 0.0f), 0.0f, 0.0f, 0.0f,
+                                   FirstPersonRotation::YawOnly, upright),
+          "yaw-only must be computable for an upright kart");
+    for (size_t i = 0; i < 3; ++i) {
+        CheckNear(rolled[4 + i], upright[4 + i], "yaw-only ignores the kart's roll");
+    }
+    CheckNear(rolled[5], 1.0f, "yaw-only keeps the horizon level");
+}
+
 } // namespace
 
 int main() {
     TestNeutralInputsProduceIdentity();
-    TestUnlevelledAnchorIsPureTranslation();
+    TestLevelCameraGivesPureTranslation();
     TestLevellingRemovesCameraPitch();
     TestAnchorRotationStaysOrthonormal();
+    TestFullRotationFollowsTheKart();
+    TestYawPitchKeepsClimbAndDropsRoll();
+    TestYawOnlyIgnoresKartRoll();
     TestNonFiniteInputIsRejected();
     TestDegenerateKartPoseIsRejected();
     if (g_failures != 0) {