Merge pull request #159 from orange-cpp/feature/color_update

Feature/color update

include/omath/collision/gjk_algorithm.hpp

@@ -14,11 +14,15 @@ namespace omath::collision
         Simplex<VertexType> simplex; // valid only if hit == true and size==4
     };
 
+    struct GjkSettings final
+    {
+        float epsilon = 1e-6f;
+        std::size_t max_iterations = 64;
+    };
     template<class ColliderInterfaceType>
     class GjkAlgorithm final
     {
         using VectorType = ColliderInterfaceType::VectorType;
-
     public:
         [[nodiscard]]
         static VectorType find_support_vertex(const ColliderInterfaceType& collider_a,
@@ -36,7 +40,8 @@ namespace omath::collision
 
         [[nodiscard]]
         static GjkHitInfo<VectorType> is_collide_with_simplex_info(const ColliderInterfaceType& collider_a,
-                                                                   const ColliderInterfaceType& collider_b)
+                                                                   const ColliderInterfaceType& collider_b,
+                                                                   const GjkSettings& settings = {})
         {
             auto support = find_support_vertex(collider_a, collider_b, VectorType{1, 0, 0});
 
@@ -45,11 +50,11 @@ namespace omath::collision
 
             auto direction = -support;
 
-            while (true)
+            for (std::size_t iteration = 0; iteration < settings.max_iterations; ++iteration)
             {
                 support = find_support_vertex(collider_a, collider_b, direction);
 
-                if (support.dot(direction) <= 0.f)
+                if (support.dot(direction) <= settings.epsilon)
                     return {false, simplex};
 
                 simplex.push_front(support);
@@ -57,6 +62,7 @@ namespace omath::collision
                 if (simplex.handle(direction))
                     return {true, simplex};
             }
+            return {false, simplex};
         }
     };
 } // namespace omath::collision

include/omath/collision/mesh_collider.hpp

@@ -46,9 +46,26 @@ namespace omath::collision
         [[nodiscard]]
         const VertexType& find_furthest_vertex(const VectorType& direction) const
         {
-            return *std::ranges::max_element(
+            // The support query arrives in world space, but vertex positions are stored
-                    m_mesh.m_vertex_buffer, [&direction](const auto& first, const auto& second)
+            // in local space.  We need argmax_v { world(v) · d }.
-                    { return first.position.dot(direction) < second.position.dot(direction); });
+            //
+            // world(v) = M·v  (ignoring translation, which is constant across vertices)
+            // world(v) · d = v · Mᵀ·d
+            //
+            // So we transform the direction to local space once — O(1) — then compare
+            // raw local positions, which is far cheaper than calling
+            // vertex_position_to_world_space (full 4×4 multiply) for every vertex.
+            //
+            // d_local = upper-left 3×3 of M, transposed, times d_world:
+            //   d_local[j] = sum_i  M.at(i,j) * d[i]   (i.e. column j of M dotted with d)
+            const auto& m = m_mesh.get_to_world_matrix();
+            const VectorType d_local = {
+                    m[0, 0] * direction.x + m[1, 0] * direction.y + m[2, 0] * direction.z,
+                    m[0, 1] * direction.x + m[1, 1] * direction.y + m[2, 1] * direction.z,
+                    m[0, 2] * direction.x + m[1, 2] * direction.y + m[2, 2] * direction.z,
+            };
+            return *std::ranges::max_element(m_mesh.m_vertex_buffer, [&d_local](const auto& first, const auto& second)
+                                             { return first.position.dot(d_local) < second.position.dot(d_local); });
         }
         MeshType m_mesh;
     };

include/omath/linear_algebra/quaternion.hpp

@@ -0,0 +1,219 @@
+//
+// Created by vlad on 3/1/2026.
+//
+#pragma once
+
+#include "omath/linear_algebra/mat.hpp"
+#include "omath/linear_algebra/vector3.hpp"
+#include <array>
+#include <cmath>
+#include <format>
+
+namespace omath
+{
+    template<class Type>
+    requires std::is_arithmetic_v<Type>
+    class Quaternion
+    {
+    public:
+        using ContainedType = Type;
+
+        Type x = static_cast<Type>(0);
+        Type y = static_cast<Type>(0);
+        Type z = static_cast<Type>(0);
+        Type w = static_cast<Type>(1);  // identity quaternion
+
+        constexpr Quaternion() noexcept = default;
+
+        constexpr Quaternion(const Type& x, const Type& y, const Type& z, const Type& w) noexcept
+            : x(x), y(y), z(z), w(w)
+        {
+        }
+
+        // Factory: build from a normalized axis and an angle in radians
+        [[nodiscard]]
+        static Quaternion from_axis_angle(const Vector3<Type>& axis, const Type& angle_rad) noexcept
+        {
+            const Type half = angle_rad / static_cast<Type>(2);
+            const Type s = std::sin(half);
+            return {axis.x * s, axis.y * s, axis.z * s, std::cos(half)};
+        }
+
+        [[nodiscard]] constexpr bool operator==(const Quaternion& other) const noexcept
+        {
+            return x == other.x && y == other.y && z == other.z && w == other.w;
+        }
+
+        [[nodiscard]] constexpr bool operator!=(const Quaternion& other) const noexcept
+        {
+            return !(*this == other);
+        }
+
+        // Hamilton product: this * other
+        [[nodiscard]] constexpr Quaternion operator*(const Quaternion& other) const noexcept
+        {
+            return {
+                w * other.x + x * other.w + y * other.z - z * other.y,
+                w * other.y - x * other.z + y * other.w + z * other.x,
+                w * other.z + x * other.y - y * other.x + z * other.w,
+                w * other.w - x * other.x - y * other.y - z * other.z,
+            };
+        }
+
+        constexpr Quaternion& operator*=(const Quaternion& other) noexcept
+        {
+            return *this = *this * other;
+        }
+
+        [[nodiscard]] constexpr Quaternion operator*(const Type& scalar) const noexcept
+        {
+            return {x * scalar, y * scalar, z * scalar, w * scalar};
+        }
+
+        constexpr Quaternion& operator*=(const Type& scalar) noexcept
+        {
+            x *= scalar;
+            y *= scalar;
+            z *= scalar;
+            w *= scalar;
+            return *this;
+        }
+
+        [[nodiscard]] constexpr Quaternion operator+(const Quaternion& other) const noexcept
+        {
+            return {x + other.x, y + other.y, z + other.z, w + other.w};
+        }
+
+        constexpr Quaternion& operator+=(const Quaternion& other) noexcept
+        {
+            x += other.x;
+            y += other.y;
+            z += other.z;
+            w += other.w;
+            return *this;
+        }
+
+        [[nodiscard]] constexpr Quaternion operator-() const noexcept
+        {
+            return {-x, -y, -z, -w};
+        }
+
+        // Conjugate: negates the vector part (x, y, z)
+        [[nodiscard]] constexpr Quaternion conjugate() const noexcept
+        {
+            return {-x, -y, -z, w};
+        }
+
+        [[nodiscard]] constexpr Type dot(const Quaternion& other) const noexcept
+        {
+            return x * other.x + y * other.y + z * other.z + w * other.w;
+        }
+
+        [[nodiscard]] constexpr Type length_sqr() const noexcept
+        {
+            return x * x + y * y + z * z + w * w;
+        }
+
+#ifndef _MSC_VER
+        [[nodiscard]] constexpr Type length() const noexcept
+        {
+            return std::sqrt(length_sqr());
+        }
+
+        [[nodiscard]] constexpr Quaternion normalized() const noexcept
+        {
+            const Type len = length();
+            return len != static_cast<Type>(0) ? *this * (static_cast<Type>(1) / len) : *this;
+        }
+#else
+        [[nodiscard]] Type length() const noexcept
+        {
+            return std::sqrt(length_sqr());
+        }
+
+        [[nodiscard]] Quaternion normalized() const noexcept
+        {
+            const Type len = length();
+            return len != static_cast<Type>(0) ? *this * (static_cast<Type>(1) / len) : *this;
+        }
+#endif
+
+        // Inverse: q* / |q|^2  (for unit quaternions inverse == conjugate)
+        [[nodiscard]] constexpr Quaternion inverse() const noexcept
+        {
+            return conjugate() * (static_cast<Type>(1) / length_sqr());
+        }
+
+        // Rotate a 3D vector: v' = q * pure(v) * q^-1
+        // Computed via Rodrigues' formula to avoid full quaternion product overhead
+        [[nodiscard]] constexpr Vector3<Type> rotate(const Vector3<Type>& v) const noexcept
+        {
+            const Vector3<Type> q_vec{x, y, z};
+            const Vector3<Type> cross = q_vec.cross(v);
+            return v + cross * (static_cast<Type>(2) * w) + q_vec.cross(cross) * static_cast<Type>(2);
+        }
+
+        // 3x3 rotation matrix from this (unit) quaternion
+        [[nodiscard]] constexpr Mat<3, 3, Type> to_rotation_matrix3() const noexcept
+        {
+            const Type xx = x * x, yy = y * y, zz = z * z;
+            const Type xy = x * y, xz = x * z, yz = y * z;
+            const Type wx = w * x, wy = w * y, wz = w * z;
+            const Type one = static_cast<Type>(1);
+            const Type two = static_cast<Type>(2);
+
+            return {
+                {one - two * (yy + zz), two * (xy - wz),       two * (xz + wy)      },
+                {two * (xy + wz),       one - two * (xx + zz), two * (yz - wx)      },
+                {two * (xz - wy),       two * (yz + wx),       one - two * (xx + yy)},
+            };
+        }
+
+        // 4x4 rotation matrix (with homogeneous row/column)
+        [[nodiscard]] constexpr Mat<4, 4, Type> to_rotation_matrix4() const noexcept
+        {
+            const Type xx = x * x, yy = y * y, zz = z * z;
+            const Type xy = x * y, xz = x * z, yz = y * z;
+            const Type wx = w * x, wy = w * y, wz = w * z;
+            const Type one = static_cast<Type>(1);
+            const Type two = static_cast<Type>(2);
+            const Type zero = static_cast<Type>(0);
+
+            return {
+                {one - two * (yy + zz), two * (xy - wz),       two * (xz + wy),       zero},
+                {two * (xy + wz),       one - two * (xx + zz), two * (yz - wx),       zero},
+                {two * (xz - wy),       two * (yz + wx),       one - two * (xx + yy), zero},
+                {zero,                  zero,                   zero,                  one },
+            };
+        }
+
+        [[nodiscard]] constexpr std::array<Type, 4> as_array() const noexcept
+        {
+            return {x, y, z, w};
+        }
+    };
+} // namespace omath
+
+template<class Type>
+struct std::formatter<omath::Quaternion<Type>> // NOLINT(*-dcl58-cpp)
+{
+    [[nodiscard]]
+    static constexpr auto parse(std::format_parse_context& ctx)
+    {
+        return ctx.begin();
+    }
+
+    template<class FormatContext>
+    [[nodiscard]]
+    static auto format(const omath::Quaternion<Type>& q, FormatContext& ctx)
+    {
+        if constexpr (std::is_same_v<typename FormatContext::char_type, char>)
+            return std::format_to(ctx.out(), "[{}, {}, {}, {}]", q.x, q.y, q.z, q.w);
+
+        if constexpr (std::is_same_v<typename FormatContext::char_type, wchar_t>)
+            return std::format_to(ctx.out(), L"[{}, {}, {}, {}]", q.x, q.y, q.z, q.w);
+
+        if constexpr (std::is_same_v<typename FormatContext::char_type, char8_t>)
+            return std::format_to(ctx.out(), u8"[{}, {}, {}, {}]", q.x, q.y, q.z, q.w);
+    }
+};

include/omath/omath.hpp

@@ -17,6 +17,9 @@
 // Matrix classes
 #include "omath/linear_algebra/mat.hpp"
 
+// Quaternion
+#include "omath/linear_algebra/quaternion.hpp"
+
 // Color functionality
 #include "omath/utility/color.hpp"
 

include/omath/utility/color.hpp

@@ -16,19 +16,28 @@ namespace omath
         float value{};
     };
 
-    class Color final : public Vector4<float>
+    class Color final
     {
+        Vector4<float> m_value;
     public:
-        constexpr Color(const float r, const float g, const float b, const float a) noexcept: Vector4(r, g, b, a)
+        constexpr const Vector4<float>& value() const
         {
-            clamp(0.f, 1.f);
+            return m_value;
+        }
+        constexpr Color(const float r, const float g, const float b, const float a) noexcept: m_value(r, g, b, a)
+        {
+            m_value.clamp(0.f, 1.f);
         }
 
+        constexpr explicit Color(const Vector4<float>& value) : m_value(value)
+        {
+            m_value.clamp(0.f, 1.f);
+        }
         constexpr explicit Color() noexcept = default;
         [[nodiscard]]
         constexpr static Color from_rgba(const uint8_t r, const uint8_t g, const uint8_t b, const uint8_t a) noexcept
         {
-            return Color{Vector4(r, g, b, a) / 255.f};
+            return Color(Vector4<float>(r, g, b, a) / 255.f);
         }
 
         [[nodiscard]]
@@ -82,9 +91,9 @@ namespace omath
         {
             Hsv hsv_data;
 
-            const float& red = x;
+            const float& red = m_value.x;
-            const float& green = y;
+            const float& green = m_value.y;
-            const float& blue = z;
+            const float& blue = m_value.z;
 
             const float max = std::max({red, green, blue});
             const float min = std::min({red, green, blue});
@@ -109,11 +118,6 @@ namespace omath
 
             return hsv_data;
         }
-
-        constexpr explicit Color(const Vector4& vec) noexcept: Vector4(vec)
-        {
-            clamp(0.f, 1.f);
-        }
         constexpr void set_hue(const float hue) noexcept
         {
             auto hsv = to_hsv();
@@ -141,7 +145,7 @@ namespace omath
         constexpr Color blend(const Color& other, float ratio) const noexcept
         {
             ratio = std::clamp(ratio, 0.f, 1.f);
-            return Color(*this * (1.f - ratio) + other * ratio);
+            return Color(this->m_value * (1.f - ratio) + other.m_value * ratio);
         }
 
         [[nodiscard]] static constexpr Color red()
@@ -160,16 +164,26 @@ namespace omath
         [[nodiscard]]
         ImColor to_im_color() const noexcept
         {
-            return {to_im_vec4()};
+            return {m_value.to_im_vec4()};
         }
 #endif
         [[nodiscard]] std::string to_string() const noexcept
         {
             return std::format("[r:{}, g:{}, b:{}, a:{}]",
-                            static_cast<int>(x * 255.f),
+                            static_cast<int>(m_value.x * 255.f),
-                            static_cast<int>(y * 255.f),
+                            static_cast<int>(m_value.y * 255.f),
-                            static_cast<int>(z * 255.f),
+                            static_cast<int>(m_value.z * 255.f),
-                            static_cast<int>(w * 255.f));
+                            static_cast<int>(m_value.w * 255.f));
+        }
+        [[nodiscard]] std::string to_rgbf_string() const noexcept
+        {
+            return std::format("[r:{}, g:{}, b:{}, a:{}]",
+                            m_value.x, m_value.y, m_value.z, m_value.w);
+        }
+        [[nodiscard]] std::string to_hsv_string() const noexcept
+        {
+            const auto [hue, saturation, value] = to_hsv();
+            return std::format("[h:{}, s:{}, v:{}]", hue, saturation, value);
         }
         [[nodiscard]] std::wstring to_wstring() const noexcept
         {
@@ -188,23 +202,55 @@ namespace omath
 template<>
 struct std::formatter<omath::Color> // NOLINT(*-dcl58-cpp)
 {
-    [[nodiscard]]
+    enum class ColorFormat { rgb, rgbf, hsv };
-    static constexpr auto parse(const std::format_parse_context& ctx)
+    ColorFormat color_format = ColorFormat::rgb;
+
+    constexpr auto parse(std::format_parse_context& ctx)
     {
-        return ctx.begin();
+        const auto it = ctx.begin();
+        const auto end = ctx.end();
+
+        if (it == end || *it == '}')
+            return it;
+
+        const std::string_view spec(it, end);
+
+        if (spec.starts_with("rgbf"))
+        {
+            color_format = ColorFormat::rgbf;
+            return it + 4;
+        }
+        if (spec.starts_with("rgb"))
+        {
+            color_format = ColorFormat::rgb;
+            return it + 3;
+        }
+        if (spec.starts_with("hsv"))
+        {
+            color_format = ColorFormat::hsv;
+            return it + 3;
+        }
+
+        throw std::format_error("Invalid format specifier for omath::Color. Use rgb, rgbf, or hsv.");
     }
 
     template<class FormatContext>
-    [[nodiscard]]
+    auto format(const omath::Color& col, FormatContext& ctx) const
-    static auto format(const omath::Color& col, FormatContext& ctx)
     {
-        if constexpr (std::is_same_v<typename FormatContext::char_type, char>)
+        std::string str;
-            return std::format_to(ctx.out(), "{}", col.to_string());
+        switch (color_format)
-        if constexpr (std::is_same_v<typename FormatContext::char_type, wchar_t>)
+        {
-            return std::format_to(ctx.out(), L"{}", col.to_wstring());
+            case ColorFormat::rgb:  str = col.to_string();      break;
+            case ColorFormat::rgbf: str = col.to_rgbf_string(); break;
+            case ColorFormat::hsv:  str = col.to_hsv_string();  break;
+        }
 
+        if constexpr (std::is_same_v<typename FormatContext::char_type, char>)
+            return std::format_to(ctx.out(), "{}", str);
+        if constexpr (std::is_same_v<typename FormatContext::char_type, wchar_t>)
+            return std::format_to(ctx.out(), L"{}", std::wstring(str.cbegin(), str.cend()));
         if constexpr (std::is_same_v<typename FormatContext::char_type, char8_t>)
-            return std::format_to(ctx.out(), u8"{}", col.to_u8string());
+            return std::format_to(ctx.out(), u8"{}", std::u8string(str.cbegin(), str.cend()));
 
         std::unreachable();
     }

tests/general/unit_test_color_grouped.cpp

@@ -26,38 +26,38 @@ protected:
 TEST_F(UnitTestColorGrouped, Constructor_Float)
 {
     constexpr Color color(0.5f, 0.5f, 0.5f, 1.0f);
-    EXPECT_FLOAT_EQ(color.x, 0.5f);
+    EXPECT_FLOAT_EQ(color.value().x, 0.5f);
-    EXPECT_FLOAT_EQ(color.y, 0.5f);
+    EXPECT_FLOAT_EQ(color.value().y, 0.5f);
-    EXPECT_FLOAT_EQ(color.z, 0.5f);
+    EXPECT_FLOAT_EQ(color.value().z, 0.5f);
-    EXPECT_FLOAT_EQ(color.w, 1.0f);
+    EXPECT_FLOAT_EQ(color.value().w, 1.0f);
 }
 
 TEST_F(UnitTestColorGrouped, Constructor_Vector4)
 {
     constexpr omath::Vector4 vec(0.2f, 0.4f, 0.6f, 0.8f);
     constexpr Color color(vec);
-    EXPECT_FLOAT_EQ(color.x, 0.2f);
+    EXPECT_FLOAT_EQ(color.value().x, 0.2f);
-    EXPECT_FLOAT_EQ(color.y, 0.4f);
+    EXPECT_FLOAT_EQ(color.value().y, 0.4f);
-    EXPECT_FLOAT_EQ(color.z, 0.6f);
+    EXPECT_FLOAT_EQ(color.value().z, 0.6f);
-    EXPECT_FLOAT_EQ(color.w, 0.8f);
+    EXPECT_FLOAT_EQ(color.value().w, 0.8f);
 }
 
 TEST_F(UnitTestColorGrouped, FromRGBA)
 {
     constexpr Color color = Color::from_rgba(128, 64, 32, 255);
-    EXPECT_FLOAT_EQ(color.x, 128.0f / 255.0f);
+    EXPECT_FLOAT_EQ(color.value().x, 128.0f / 255.0f);
-    EXPECT_FLOAT_EQ(color.y, 64.0f / 255.0f);
+    EXPECT_FLOAT_EQ(color.value().y, 64.0f / 255.0f);
-    EXPECT_FLOAT_EQ(color.z, 32.0f / 255.0f);
+    EXPECT_FLOAT_EQ(color.value().z, 32.0f / 255.0f);
-    EXPECT_FLOAT_EQ(color.w, 1.0f);
+    EXPECT_FLOAT_EQ(color.value().w, 1.0f);
 }
 
 TEST_F(UnitTestColorGrouped, FromHSV)
 {
     constexpr Color color = Color::from_hsv(0.0f, 1.0f, 1.0f); // Red in HSV
-    EXPECT_FLOAT_EQ(color.x, 1.0f);
+    EXPECT_FLOAT_EQ(color.value().x, 1.0f);
-    EXPECT_FLOAT_EQ(color.y, 0.0f);
+    EXPECT_FLOAT_EQ(color.value().y, 0.0f);
-    EXPECT_FLOAT_EQ(color.z, 0.0f);
+    EXPECT_FLOAT_EQ(color.value().z, 0.0f);
-    EXPECT_FLOAT_EQ(color.w, 1.0f);
+    EXPECT_FLOAT_EQ(color.value().w, 1.0f);
 }
 
 TEST_F(UnitTestColorGrouped, ToHSV)
@@ -71,10 +71,10 @@ TEST_F(UnitTestColorGrouped, ToHSV)
 TEST_F(UnitTestColorGrouped, Blend)
 {
     const Color blended = color1.blend(color2, 0.5f);
-    EXPECT_FLOAT_EQ(blended.x, 0.5f);
+    EXPECT_FLOAT_EQ(blended.value().x, 0.5f);
-    EXPECT_FLOAT_EQ(blended.y, 0.5f);
+    EXPECT_FLOAT_EQ(blended.value().y, 0.5f);
-    EXPECT_FLOAT_EQ(blended.z, 0.0f);
+    EXPECT_FLOAT_EQ(blended.value().z, 0.0f);
-    EXPECT_FLOAT_EQ(blended.w, 1.0f);
+    EXPECT_FLOAT_EQ(blended.value().w, 1.0f);
 }
 
 TEST_F(UnitTestColorGrouped, PredefinedColors)
@@ -83,20 +83,20 @@ TEST_F(UnitTestColorGrouped, PredefinedColors)
     constexpr Color green = Color::green();
     constexpr Color blue = Color::blue();
 
-    EXPECT_FLOAT_EQ(red.x, 1.0f);
+    EXPECT_FLOAT_EQ(red.value().x, 1.0f);
-    EXPECT_FLOAT_EQ(red.y, 0.0f);
+    EXPECT_FLOAT_EQ(red.value().y, 0.0f);
-    EXPECT_FLOAT_EQ(red.z, 0.0f);
+    EXPECT_FLOAT_EQ(red.value().z, 0.0f);
-    EXPECT_FLOAT_EQ(red.w, 1.0f);
+    EXPECT_FLOAT_EQ(red.value().w, 1.0f);
 
-    EXPECT_FLOAT_EQ(green.x, 0.0f);
+    EXPECT_FLOAT_EQ(green.value().x, 0.0f);
-    EXPECT_FLOAT_EQ(green.y, 1.0f);
+    EXPECT_FLOAT_EQ(green.value().y, 1.0f);
-    EXPECT_FLOAT_EQ(green.z, 0.0f);
+    EXPECT_FLOAT_EQ(green.value().z, 0.0f);
-    EXPECT_FLOAT_EQ(green.w, 1.0f);
+    EXPECT_FLOAT_EQ(green.value().w, 1.0f);
 
-    EXPECT_FLOAT_EQ(blue.x, 0.0f);
+    EXPECT_FLOAT_EQ(blue.value().x, 0.0f);
-    EXPECT_FLOAT_EQ(blue.y, 0.0f);
+    EXPECT_FLOAT_EQ(blue.value().y, 0.0f);
-    EXPECT_FLOAT_EQ(blue.z, 1.0f);
+    EXPECT_FLOAT_EQ(blue.value().z, 1.0f);
-    EXPECT_FLOAT_EQ(blue.w, 1.0f);
+    EXPECT_FLOAT_EQ(blue.value().w, 1.0f);
 }
 
 TEST_F(UnitTestColorGrouped, BlendVector3)
@@ -104,9 +104,9 @@ TEST_F(UnitTestColorGrouped, BlendVector3)
     constexpr Color v1(1.0f, 0.0f, 0.0f, 1.f); // Red
     constexpr Color v2(0.0f, 1.0f, 0.0f, 1.f); // Green
     constexpr Color blended = v1.blend(v2, 0.5f);
-    EXPECT_FLOAT_EQ(blended.x, 0.5f);
+    EXPECT_FLOAT_EQ(blended.value().x, 0.5f);
-    EXPECT_FLOAT_EQ(blended.y, 0.5f);
+    EXPECT_FLOAT_EQ(blended.value().y, 0.5f);
-    EXPECT_FLOAT_EQ(blended.z, 0.0f);
+    EXPECT_FLOAT_EQ(blended.value().z, 0.0f);
 }
 
 // From unit_test_color_extra.cpp
@@ -148,37 +148,37 @@ TEST(UnitTestColorGrouped_Extra, BlendEdgeCases)
     constexpr Color a = Color::red();
     constexpr Color b = Color::blue();
     constexpr auto r0 = a.blend(b, 0.f);
-    EXPECT_FLOAT_EQ(r0.x, a.x);
+    EXPECT_FLOAT_EQ(r0.value().x, a.value().x);
     constexpr auto r1 = a.blend(b, 1.f);
-    EXPECT_FLOAT_EQ(r1.x, b.x);
+    EXPECT_FLOAT_EQ(r1.value().x, b.value().x);
 }
 
 // From unit_test_color_more.cpp
 TEST(UnitTestColorGrouped_More, DefaultCtorIsZero)
 {
     constexpr Color c;
-    EXPECT_FLOAT_EQ(c.x, 0.0f);
+    EXPECT_FLOAT_EQ(c.value().x, 0.0f);
-    EXPECT_FLOAT_EQ(c.y, 0.0f);
+    EXPECT_FLOAT_EQ(c.value().y, 0.0f);
-    EXPECT_FLOAT_EQ(c.z, 0.0f);
+    EXPECT_FLOAT_EQ(c.value().z, 0.0f);
-    EXPECT_FLOAT_EQ(c.w, 0.0f);
+    EXPECT_FLOAT_EQ(c.value().w, 0.0f);
 }
 
 TEST(UnitTestColorGrouped_More, FloatCtorAndClampForRGB)
 {
     constexpr Color c(1.2f, -0.5f, 0.5f, 2.0f);
-    EXPECT_FLOAT_EQ(c.x, 1.0f);
+    EXPECT_FLOAT_EQ(c.value().x, 1.0f);
-    EXPECT_FLOAT_EQ(c.y, 0.0f);
+    EXPECT_FLOAT_EQ(c.value().y, 0.0f);
-    EXPECT_FLOAT_EQ(c.z, 0.5f);
+    EXPECT_FLOAT_EQ(c.value().z, 0.5f);
-    EXPECT_FLOAT_EQ(c.w, 2.0f);
+    EXPECT_FLOAT_EQ(c.value().w, 2.0f);
 }
 
 TEST(UnitTestColorGrouped_More, FromRgbaProducesScaledComponents)
 {
     constexpr Color c = Color::from_rgba(25u, 128u, 230u, 64u);
-    EXPECT_NEAR(c.x, 25.0f/255.0f, 1e-6f);
+    EXPECT_NEAR(c.value().x, 25.0f/255.0f, 1e-6f);
-    EXPECT_NEAR(c.y, 128.0f/255.0f, 1e-6f);
+    EXPECT_NEAR(c.value().y, 128.0f/255.0f, 1e-6f);
-    EXPECT_NEAR(c.z, 230.0f/255.0f, 1e-6f);
+    EXPECT_NEAR(c.value().z, 230.0f/255.0f, 1e-6f);
-    EXPECT_NEAR(c.w, 64.0f/255.0f, 1e-6f);
+    EXPECT_NEAR(c.value().w, 64.0f/255.0f, 1e-6f);
 }
 
 TEST(UnitTestColorGrouped_More, BlendProducesIntermediate)
@@ -186,10 +186,10 @@ TEST(UnitTestColorGrouped_More, BlendProducesIntermediate)
     constexpr Color c0(0.0f, 0.0f, 0.0f, 1.0f);
     constexpr Color c1(1.0f, 1.0f, 1.0f, 0.0f);
     constexpr Color mid = c0.blend(c1, 0.5f);
-    EXPECT_FLOAT_EQ(mid.x, 0.5f);
+    EXPECT_FLOAT_EQ(mid.value().x, 0.5f);
-    EXPECT_FLOAT_EQ(mid.y, 0.5f);
+    EXPECT_FLOAT_EQ(mid.value().y, 0.5f);
-    EXPECT_FLOAT_EQ(mid.z, 0.5f);
+    EXPECT_FLOAT_EQ(mid.value().z, 0.5f);
-    EXPECT_FLOAT_EQ(mid.w, 0.5f);
+    EXPECT_FLOAT_EQ(mid.value().w, 0.5f);
 }
 
 TEST(UnitTestColorGrouped_More, HsvRoundTrip)
@@ -197,9 +197,9 @@ TEST(UnitTestColorGrouped_More, HsvRoundTrip)
     constexpr Color red = Color::red();
     const auto hsv = red.to_hsv();
     const Color back = Color::from_hsv(hsv);
-    EXPECT_NEAR(back.x, 1.0f, 1e-6f);
+    EXPECT_NEAR(back.value().x, 1.0f, 1e-6f);
-    EXPECT_NEAR(back.y, 0.0f, 1e-6f);
+    EXPECT_NEAR(back.value().y, 0.0f, 1e-6f);
-    EXPECT_NEAR(back.z, 0.0f, 1e-6f);
+    EXPECT_NEAR(back.value().z, 0.0f, 1e-6f);
 }
 
 TEST(UnitTestColorGrouped_More, ToStringContainsComponents)
@@ -230,18 +230,18 @@ TEST(UnitTestColorGrouped_More2, FromHsvCases)
     auto check_hue = [&](float h) {
         SCOPED_TRACE(::testing::Message() << "h=" << h);
         Color c = Color::from_hsv(h, 1.f, 1.f);
-        EXPECT_TRUE(std::isfinite(c.x));
+        EXPECT_TRUE(std::isfinite(c.value().x));
-        EXPECT_TRUE(std::isfinite(c.y));
+        EXPECT_TRUE(std::isfinite(c.value().y));
-        EXPECT_TRUE(std::isfinite(c.z));
+        EXPECT_TRUE(std::isfinite(c.value().z));
-        EXPECT_GE(c.x, -eps);
+        EXPECT_GE(c.value().x, -eps);
-        EXPECT_LE(c.x, 1.f + eps);
+        EXPECT_LE(c.value().x, 1.f + eps);
-        EXPECT_GE(c.y, -eps);
+        EXPECT_GE(c.value().y, -eps);
-        EXPECT_LE(c.y, 1.f + eps);
+        EXPECT_LE(c.value().y, 1.f + eps);
-        EXPECT_GE(c.z, -eps);
+        EXPECT_GE(c.value().z, -eps);
-        EXPECT_LE(c.z, 1.f + eps);
+        EXPECT_LE(c.value().z, 1.f + eps);
 
-        float mx = std::max({c.x, c.y, c.z});
+        float mx = std::max({c.value().x, c.value().y, c.value().z});
-        float mn = std::min({c.x, c.y, c.z});
+        float mn = std::min({c.value().x, c.value().y, c.value().z});
         EXPECT_GE(mx, 0.999f);
         EXPECT_LE(mn, 1e-3f + 1e-4f);
     };
@@ -261,13 +261,13 @@ TEST(UnitTestColorGrouped_More2, ToHsvAndSetters)
     EXPECT_NEAR(hsv.value, 0.6f, 1e-6f);
 
     c.set_hue(0.0f);
-    EXPECT_TRUE(std::isfinite(c.x));
+    EXPECT_TRUE(std::isfinite(c.value().x));
 
     c.set_saturation(0.0f);
-    EXPECT_TRUE(std::isfinite(c.y));
+    EXPECT_TRUE(std::isfinite(c.value().y));
 
     c.set_value(0.5f);
-    EXPECT_TRUE(std::isfinite(c.z));
+    EXPECT_TRUE(std::isfinite(c.value().z));
 }
 
 TEST(UnitTestColorGrouped_More2, BlendAndStaticColors)
@@ -275,14 +275,14 @@ TEST(UnitTestColorGrouped_More2, BlendAndStaticColors)
     constexpr Color a = Color::red();
     constexpr Color b = Color::blue();
     constexpr auto mid = a.blend(b, 0.5f);
-    EXPECT_GT(mid.x, 0.f);
+    EXPECT_GT(mid.value().x, 0.f);
-    EXPECT_GT(mid.z, 0.f);
+    EXPECT_GT(mid.value().z, 0.f);
 
     constexpr auto all_a = a.blend(b, -1.f);
-    EXPECT_NEAR(all_a.x, a.x, 1e-6f);
+    EXPECT_NEAR(all_a.value().x, a.value().x, 1e-6f);
 
     constexpr auto all_b = a.blend(b, 2.f);
-    EXPECT_NEAR(all_b.z, b.z, 1e-6f);
+    EXPECT_NEAR(all_b.value().z, b.value().z, 1e-6f);
 }
 
 TEST(UnitTestColorGrouped_More2, FormatterUsesToString)
@@ -291,3 +291,35 @@ TEST(UnitTestColorGrouped_More2, FormatterUsesToString)
     const auto formatted = std::format("{}", c);
     EXPECT_NE(formatted.find("r:10"), std::string::npos);
 }
+
+TEST(UnitTestColorGrouped_More2, FormatterRgb)
+{
+    constexpr Color c = Color::from_rgba(255, 128, 0, 64);
+    const auto s = std::format("{:rgb}", c);
+    EXPECT_NE(s.find("r:255"), std::string::npos);
+    EXPECT_NE(s.find("g:128"), std::string::npos);
+    EXPECT_NE(s.find("b:0"), std::string::npos);
+    EXPECT_NE(s.find("a:64"), std::string::npos);
+}
+
+TEST(UnitTestColorGrouped_More2, FormatterRgbf)
+{
+    constexpr Color c(0.5f, 0.25f, 1.0f, 0.75f);
+    const auto s = std::format("{:rgbf}", c);
+    EXPECT_NE(s.find("r:"), std::string::npos);
+    EXPECT_NE(s.find("g:"), std::string::npos);
+    EXPECT_NE(s.find("b:"), std::string::npos);
+    EXPECT_NE(s.find("a:"), std::string::npos);
+    // Values should be in [0,1] float range, not 0-255
+    EXPECT_EQ(s.find("r:127"), std::string::npos);
+    EXPECT_EQ(s.find("r:255"), std::string::npos);
+}
+
+TEST(UnitTestColorGrouped_More2, FormatterHsv)
+{
+    const Color c = Color::red();
+    const auto s = std::format("{:hsv}", c);
+    EXPECT_NE(s.find("h:"), std::string::npos);
+    EXPECT_NE(s.find("s:"), std::string::npos);
+    EXPECT_NE(s.find("v:"), std::string::npos);
+}

tests/general/unit_test_quaternion.cpp

@@ -0,0 +1,402 @@
+//
+// Created by vlad on 3/1/2026.
+//
+#include <omath/linear_algebra/quaternion.hpp>
+#include <cmath>
+#include <gtest/gtest.h>
+#include <numbers>
+
+using namespace omath;
+
+static constexpr float kEps = 1e-5f;
+
+// ── Helpers ──────────────────────────────────────────────────────────────────
+
+static void expect_quat_near(const Quaternion<float>& a, const Quaternion<float>& b, float eps = kEps)
+{
+    EXPECT_NEAR(a.x, b.x, eps);
+    EXPECT_NEAR(a.y, b.y, eps);
+    EXPECT_NEAR(a.z, b.z, eps);
+    EXPECT_NEAR(a.w, b.w, eps);
+}
+
+static void expect_vec3_near(const Vector3<float>& a, const Vector3<float>& b, float eps = kEps)
+{
+    EXPECT_NEAR(a.x, b.x, eps);
+    EXPECT_NEAR(a.y, b.y, eps);
+    EXPECT_NEAR(a.z, b.z, eps);
+}
+
+// ── Constructors ─────────────────────────────────────────────────────────────
+
+TEST(Quaternion, DefaultConstructorIsIdentity)
+{
+    constexpr Quaternion<float> q;
+    EXPECT_FLOAT_EQ(q.x, 0.f);
+    EXPECT_FLOAT_EQ(q.y, 0.f);
+    EXPECT_FLOAT_EQ(q.z, 0.f);
+    EXPECT_FLOAT_EQ(q.w, 1.f);
+}
+
+TEST(Quaternion, ValueConstructor)
+{
+    constexpr Quaternion<float> q{1.f, 2.f, 3.f, 4.f};
+    EXPECT_FLOAT_EQ(q.x, 1.f);
+    EXPECT_FLOAT_EQ(q.y, 2.f);
+    EXPECT_FLOAT_EQ(q.z, 3.f);
+    EXPECT_FLOAT_EQ(q.w, 4.f);
+}
+
+TEST(Quaternion, DoubleInstantiation)
+{
+    constexpr Quaternion<double> q{0.0, 0.0, 0.0, 1.0};
+    EXPECT_DOUBLE_EQ(q.w, 1.0);
+}
+
+// ── Equality ─────────────────────────────────────────────────────────────────
+
+TEST(Quaternion, EqualityOperators)
+{
+    constexpr Quaternion<float> a{1.f, 2.f, 3.f, 4.f};
+    constexpr Quaternion<float> b{1.f, 2.f, 3.f, 4.f};
+    constexpr Quaternion<float> c{1.f, 2.f, 3.f, 5.f};
+
+    EXPECT_TRUE(a == b);
+    EXPECT_FALSE(a == c);
+    EXPECT_FALSE(a != b);
+    EXPECT_TRUE(a != c);
+}
+
+// ── Arithmetic ───────────────────────────────────────────────────────────────
+
+TEST(Quaternion, ScalarMultiply)
+{
+    constexpr Quaternion<float> q{1.f, 2.f, 3.f, 4.f};
+    constexpr auto r = q * 2.f;
+    EXPECT_FLOAT_EQ(r.x, 2.f);
+    EXPECT_FLOAT_EQ(r.y, 4.f);
+    EXPECT_FLOAT_EQ(r.z, 6.f);
+    EXPECT_FLOAT_EQ(r.w, 8.f);
+}
+
+TEST(Quaternion, ScalarMultiplyAssign)
+{
+    Quaternion<float> q{1.f, 2.f, 3.f, 4.f};
+    q *= 3.f;
+    EXPECT_FLOAT_EQ(q.x, 3.f);
+    EXPECT_FLOAT_EQ(q.y, 6.f);
+    EXPECT_FLOAT_EQ(q.z, 9.f);
+    EXPECT_FLOAT_EQ(q.w, 12.f);
+}
+
+TEST(Quaternion, Addition)
+{
+    constexpr Quaternion<float> a{1.f, 2.f, 3.f, 4.f};
+    constexpr Quaternion<float> b{4.f, 3.f, 2.f, 1.f};
+    constexpr auto r = a + b;
+    EXPECT_FLOAT_EQ(r.x, 5.f);
+    EXPECT_FLOAT_EQ(r.y, 5.f);
+    EXPECT_FLOAT_EQ(r.z, 5.f);
+    EXPECT_FLOAT_EQ(r.w, 5.f);
+}
+
+TEST(Quaternion, AdditionAssign)
+{
+    Quaternion<float> a{1.f, 0.f, 0.f, 0.f};
+    const Quaternion<float> b{0.f, 1.f, 0.f, 0.f};
+    a += b;
+    EXPECT_FLOAT_EQ(a.x, 1.f);
+    EXPECT_FLOAT_EQ(a.y, 1.f);
+}
+
+TEST(Quaternion, UnaryNegation)
+{
+    constexpr Quaternion<float> q{1.f, -2.f, 3.f, -4.f};
+    constexpr auto r = -q;
+    EXPECT_FLOAT_EQ(r.x, -1.f);
+    EXPECT_FLOAT_EQ(r.y,  2.f);
+    EXPECT_FLOAT_EQ(r.z, -3.f);
+    EXPECT_FLOAT_EQ(r.w,  4.f);
+}
+
+// ── Hamilton product ──────────────────────────────────────────────────────────
+
+TEST(Quaternion, MultiplyByIdentityIsNoop)
+{
+    constexpr Quaternion<float> identity;
+    constexpr Quaternion<float> q{0.5f, 0.5f, 0.5f, 0.5f};
+    expect_quat_near(q * identity, q);
+    expect_quat_near(identity * q, q);
+}
+
+TEST(Quaternion, MultiplyAssign)
+{
+    constexpr Quaternion<float> identity;
+    Quaternion<float> q{0.5f, 0.5f, 0.5f, 0.5f};
+    q *= identity;
+    expect_quat_near(q, {0.5f, 0.5f, 0.5f, 0.5f});
+}
+
+TEST(Quaternion, MultiplyKnownResult)
+{
+    // i * j = k  →  (1,0,0,0) * (0,1,0,0) = (0,0,1,0)
+    constexpr Quaternion<float> i{1.f, 0.f, 0.f, 0.f};
+    constexpr Quaternion<float> j{0.f, 1.f, 0.f, 0.f};
+    constexpr auto k = i * j;
+    EXPECT_FLOAT_EQ(k.x, 0.f);
+    EXPECT_FLOAT_EQ(k.y, 0.f);
+    EXPECT_FLOAT_EQ(k.z, 1.f);
+    EXPECT_FLOAT_EQ(k.w, 0.f);
+}
+
+TEST(Quaternion, MultiplyByInverseGivesIdentity)
+{
+    const Quaternion<float> q = Quaternion<float>::from_axis_angle({0.f, 0.f, 1.f},
+                                                                     std::numbers::pi_v<float> / 3.f);
+    const auto result = q * q.inverse();
+    expect_quat_near(result, Quaternion<float>{});
+}
+
+// ── Conjugate ────────────────────────────────────────────────────────────────
+
+TEST(Quaternion, Conjugate)
+{
+    constexpr Quaternion<float> q{1.f, 2.f, 3.f, 4.f};
+    constexpr auto c = q.conjugate();
+    EXPECT_FLOAT_EQ(c.x, -1.f);
+    EXPECT_FLOAT_EQ(c.y, -2.f);
+    EXPECT_FLOAT_EQ(c.z, -3.f);
+    EXPECT_FLOAT_EQ(c.w,  4.f);
+}
+
+TEST(Quaternion, ConjugateOfIdentityIsIdentity)
+{
+    constexpr Quaternion<float> id;
+    constexpr auto c = id.conjugate();
+    EXPECT_FLOAT_EQ(c.x, 0.f);
+    EXPECT_FLOAT_EQ(c.y, 0.f);
+    EXPECT_FLOAT_EQ(c.z, 0.f);
+    EXPECT_FLOAT_EQ(c.w, 1.f);
+}
+
+// ── Dot / length ─────────────────────────────────────────────────────────────
+
+TEST(Quaternion, Dot)
+{
+    constexpr Quaternion<float> a{1.f, 0.f, 0.f, 0.f};
+    constexpr Quaternion<float> b{0.f, 1.f, 0.f, 0.f};
+    EXPECT_FLOAT_EQ(a.dot(b), 0.f);
+    EXPECT_FLOAT_EQ(a.dot(a), 1.f);
+}
+
+TEST(Quaternion, LengthSqrIdentity)
+{
+    constexpr Quaternion<float> id;
+    EXPECT_FLOAT_EQ(id.length_sqr(), 1.f);
+}
+
+TEST(Quaternion, LengthSqrGeneral)
+{
+    constexpr Quaternion<float> q{1.f, 2.f, 3.f, 4.f};
+    EXPECT_FLOAT_EQ(q.length_sqr(), 30.f);
+}
+
+TEST(Quaternion, LengthIdentity)
+{
+    const Quaternion<float> id;
+    EXPECT_NEAR(id.length(), 1.f, kEps);
+}
+
+TEST(Quaternion, Normalized)
+{
+    const Quaternion<float> q{1.f, 1.f, 1.f, 1.f};
+    const auto n = q.normalized();
+    EXPECT_NEAR(n.length(), 1.f, kEps);
+    EXPECT_NEAR(n.x, 0.5f, kEps);
+    EXPECT_NEAR(n.y, 0.5f, kEps);
+    EXPECT_NEAR(n.z, 0.5f, kEps);
+    EXPECT_NEAR(n.w, 0.5f, kEps);
+}
+
+TEST(Quaternion, NormalizedOfZeroLengthReturnsSelf)
+{
+    // length_sqr = 0 would be UB, but zero-vector part + zero w is degenerate;
+    // we just verify the guard branch (divides by zero) doesn't crash by
+    // keeping length > 0 via the default constructor path.
+    const Quaternion<float> unit;
+    const auto n = unit.normalized();
+    expect_quat_near(n, unit);
+}
+
+// ── Inverse ───────────────────────────────────────────────────────────────────
+
+TEST(Quaternion, InverseOfUnitIsConjugate)
+{
+    const Quaternion<float> q = Quaternion<float>::from_axis_angle({1.f, 0.f, 0.f},
+                                                                     std::numbers::pi_v<float> / 4.f);
+    const auto inv = q.inverse();
+    const auto conj = q.conjugate();
+    expect_quat_near(inv, conj);
+}
+
+// ── from_axis_angle ──────────────────────────────────────────────────────────
+
+TEST(Quaternion, FromAxisAngleZeroAngleIsIdentity)
+{
+    const auto q = Quaternion<float>::from_axis_angle({1.f, 0.f, 0.f}, 0.f);
+    EXPECT_NEAR(q.x, 0.f, kEps);
+    EXPECT_NEAR(q.y, 0.f, kEps);
+    EXPECT_NEAR(q.z, 0.f, kEps);
+    EXPECT_NEAR(q.w, 1.f, kEps);
+}
+
+TEST(Quaternion, FromAxisAngle90DegZ)
+{
+    const float half_pi = std::numbers::pi_v<float> / 2.f;
+    const auto q = Quaternion<float>::from_axis_angle({0.f, 0.f, 1.f}, half_pi);
+    const float s = std::sin(half_pi / 2.f);
+    const float c = std::cos(half_pi / 2.f);
+    EXPECT_NEAR(q.x, 0.f, kEps);
+    EXPECT_NEAR(q.y, 0.f, kEps);
+    EXPECT_NEAR(q.z, s,   kEps);
+    EXPECT_NEAR(q.w, c,   kEps);
+}
+
+// ── rotate ───────────────────────────────────────────────────────────────────
+
+TEST(Quaternion, RotateByIdentityIsNoop)
+{
+    constexpr Quaternion<float> id;
+    constexpr Vector3<float> v{1.f, 2.f, 3.f};
+    const auto r = id.rotate(v);
+    expect_vec3_near(r, v);
+}
+
+TEST(Quaternion, Rotate90DegAroundZ)
+{
+    // Rotating (1,0,0) by 90° around Z should give (0,1,0)
+    const auto q = Quaternion<float>::from_axis_angle({0.f, 0.f, 1.f}, std::numbers::pi_v<float> / 2.f);
+    const auto r = q.rotate({1.f, 0.f, 0.f});
+    expect_vec3_near(r, {0.f, 1.f, 0.f});
+}
+
+TEST(Quaternion, Rotate180DegAroundY)
+{
+    // Rotating (1,0,0) by 180° around Y should give (-1,0,0)
+    const auto q = Quaternion<float>::from_axis_angle({0.f, 1.f, 0.f}, std::numbers::pi_v<float>);
+    const auto r = q.rotate({1.f, 0.f, 0.f});
+    expect_vec3_near(r, {-1.f, 0.f, 0.f});
+}
+
+TEST(Quaternion, Rotate90DegAroundX)
+{
+    // Rotating (0,1,0) by 90° around X should give (0,0,1)
+    const auto q = Quaternion<float>::from_axis_angle({1.f, 0.f, 0.f}, std::numbers::pi_v<float> / 2.f);
+    const auto r = q.rotate({0.f, 1.f, 0.f});
+    expect_vec3_near(r, {0.f, 0.f, 1.f});
+}
+
+// ── to_rotation_matrix3 ───────────────────────────────────────────────────────
+
+TEST(Quaternion, RotationMatrix3FromIdentityIsIdentityMatrix)
+{
+    constexpr Quaternion<float> id;
+    constexpr auto m = id.to_rotation_matrix3();
+    for (size_t i = 0; i < 3; ++i)
+        for (size_t j = 0; j < 3; ++j)
+            EXPECT_NEAR(m.at(i, j), i == j ? 1.f : 0.f, kEps);
+}
+
+TEST(Quaternion, RotationMatrix3From90DegZ)
+{
+    //  Expected:  | 0 -1  0 |
+    //             | 1  0  0 |
+    //             | 0  0  1 |
+    const auto q = Quaternion<float>::from_axis_angle({0.f, 0.f, 1.f}, std::numbers::pi_v<float> / 2.f);
+    const auto m = q.to_rotation_matrix3();
+    EXPECT_NEAR(m.at(0, 0),  0.f, kEps);
+    EXPECT_NEAR(m.at(0, 1), -1.f, kEps);
+    EXPECT_NEAR(m.at(0, 2),  0.f, kEps);
+    EXPECT_NEAR(m.at(1, 0),  1.f, kEps);
+    EXPECT_NEAR(m.at(1, 1),  0.f, kEps);
+    EXPECT_NEAR(m.at(1, 2),  0.f, kEps);
+    EXPECT_NEAR(m.at(2, 0),  0.f, kEps);
+    EXPECT_NEAR(m.at(2, 1),  0.f, kEps);
+    EXPECT_NEAR(m.at(2, 2),  1.f, kEps);
+}
+
+TEST(Quaternion, RotationMatrix3ConsistentWithRotate)
+{
+    // Matrix-vector multiply must agree with the rotate() method
+    const auto q = Quaternion<float>::from_axis_angle({1.f, 1.f, 0.f}, std::numbers::pi_v<float> / 3.f);
+    const Vector3<float> v{2.f, -1.f, 0.5f};
+
+    const auto rotated = q.rotate(v);
+    const auto m = q.to_rotation_matrix3();
+
+    // manual mat-vec multiply (row-major)
+    const float rx = m.at(0, 0) * v.x + m.at(0, 1) * v.y + m.at(0, 2) * v.z;
+    const float ry = m.at(1, 0) * v.x + m.at(1, 1) * v.y + m.at(1, 2) * v.z;
+    const float rz = m.at(2, 0) * v.x + m.at(2, 1) * v.y + m.at(2, 2) * v.z;
+
+    EXPECT_NEAR(rotated.x, rx, kEps);
+    EXPECT_NEAR(rotated.y, ry, kEps);
+    EXPECT_NEAR(rotated.z, rz, kEps);
+}
+
+// ── to_rotation_matrix4 ───────────────────────────────────────────────────────
+
+TEST(Quaternion, RotationMatrix4FromIdentityIsIdentityMatrix)
+{
+    constexpr Quaternion<float> id;
+    constexpr auto m = id.to_rotation_matrix4();
+    for (size_t i = 0; i < 4; ++i)
+        for (size_t j = 0; j < 4; ++j)
+            EXPECT_NEAR(m.at(i, j), i == j ? 1.f : 0.f, kEps);
+}
+
+TEST(Quaternion, RotationMatrix4HomogeneousRowAndColumn)
+{
+    const auto q = Quaternion<float>::from_axis_angle({1.f, 0.f, 0.f}, std::numbers::pi_v<float> / 5.f);
+    const auto m = q.to_rotation_matrix4();
+
+    // Last row and last column must be (0,0,0,1)
+    for (size_t i = 0; i < 3; ++i)
+    {
+        EXPECT_NEAR(m.at(3, i), 0.f, kEps);
+        EXPECT_NEAR(m.at(i, 3), 0.f, kEps);
+    }
+    EXPECT_NEAR(m.at(3, 3), 1.f, kEps);
+}
+
+TEST(Quaternion, RotationMatrix4Upper3x3MatchesMatrix3)
+{
+    const auto q = Quaternion<float>::from_axis_angle({0.f, 1.f, 0.f}, std::numbers::pi_v<float> / 7.f);
+    const auto m3 = q.to_rotation_matrix3();
+    const auto m4 = q.to_rotation_matrix4();
+
+    for (size_t i = 0; i < 3; ++i)
+        for (size_t j = 0; j < 3; ++j)
+            EXPECT_NEAR(m4.at(i, j), m3.at(i, j), kEps);
+}
+
+// ── as_array ──────────────────────────────────────────────────────────────────
+
+TEST(Quaternion, AsArray)
+{
+    constexpr Quaternion<float> q{1.f, 2.f, 3.f, 4.f};
+    constexpr auto arr = q.as_array();
+    EXPECT_FLOAT_EQ(arr[0], 1.f);
+    EXPECT_FLOAT_EQ(arr[1], 2.f);
+    EXPECT_FLOAT_EQ(arr[2], 3.f);
+    EXPECT_FLOAT_EQ(arr[3], 4.f);
+}
+
+// ── std::formatter ────────────────────────────────────────────────────────────
+
+TEST(Quaternion, Formatter)
+{
+    const Quaternion<float> q{1.f, 2.f, 3.f, 4.f};
+    const auto s = std::format("{}", q);
+    EXPECT_EQ(s, "[1, 2, 3, 4]");
+}