Merge pull request #185 from orange-cpp/feature/unreal-engine-projection-fix

Feature/unreal engine projection fix

include/omath/engines/unreal_engine/camera.hpp

@@ -9,5 +9,5 @@
 
 namespace omath::unreal_engine
 {
-    using Camera = projection::Camera<Mat4X4, ViewAngles, CameraTrait, NDCDepthRange::ZERO_TO_ONE, {.inverted_right = true}>;
+    using Camera = projection::Camera<Mat4X4, ViewAngles, CameraTrait, NDCDepthRange::ZERO_TO_ONE>;
 } // namespace omath::unreal_engine

include/omath/linear_algebra/mat.hpp

@@ -707,6 +707,59 @@ namespace omath
         else
             std::unreachable();
     }
+
+    // Horizontal-FOV variants — use these when the engine reports FOV as
+    // horizontal (UE's FMinimalViewInfo::FOV, Quake-family fov_x, etc.).
+    // X and Y scales derived as: X = 1 / tan(hfov/2), Y = aspect / tan(hfov/2).
+    template<class Type = float, MatStoreType St = MatStoreType::ROW_MAJOR,
+             NDCDepthRange DepthRange = NDCDepthRange::NEGATIVE_ONE_TO_ONE>
+    [[nodiscard]]
+    Mat<4, 4, Type, St> mat_perspective_left_handed_horizontal_fov(const float horizontal_fov,
+                                                                   const float aspect_ratio, const float near,
+                                                                   const float far) noexcept
+    {
+        const float inv_tan_half_hfov = 1.f / std::tan(angles::degrees_to_radians(horizontal_fov) / 2.f);
+        const float x_axis = inv_tan_half_hfov;
+        const float y_axis = inv_tan_half_hfov * aspect_ratio;
+
+        if constexpr (DepthRange == NDCDepthRange::ZERO_TO_ONE)
+            return {{x_axis, 0.f,    0.f,                          0.f},
+                    {0.f,    y_axis, 0.f,                          0.f},
+                    {0.f,    0.f,    far / (far - near),          -(near * far) / (far - near)},
+                    {0.f,    0.f,    1.f,                          0.f}};
+        else if constexpr (DepthRange == NDCDepthRange::NEGATIVE_ONE_TO_ONE)
+            return {{x_axis, 0.f,    0.f,                                  0.f},
+                    {0.f,    y_axis, 0.f,                                  0.f},
+                    {0.f,    0.f,    (far + near) / (far - near),         -(2.f * near * far) / (far - near)},
+                    {0.f,    0.f,    1.f,                                  0.f}};
+        else
+            std::unreachable();
+    }
+
+    template<class Type = float, MatStoreType St = MatStoreType::ROW_MAJOR,
+             NDCDepthRange DepthRange = NDCDepthRange::NEGATIVE_ONE_TO_ONE>
+    [[nodiscard]]
+    Mat<4, 4, Type, St> mat_perspective_right_handed_horizontal_fov(const float horizontal_fov,
+                                                                    const float aspect_ratio, const float near,
+                                                                    const float far) noexcept
+    {
+        const float inv_tan_half_hfov = 1.f / std::tan(angles::degrees_to_radians(horizontal_fov) / 2.f);
+        const float x_axis = inv_tan_half_hfov;
+        const float y_axis = inv_tan_half_hfov * aspect_ratio;
+
+        if constexpr (DepthRange == NDCDepthRange::ZERO_TO_ONE)
+            return {{x_axis, 0.f,    0.f,                          0.f},
+                    {0.f,    y_axis, 0.f,                          0.f},
+                    {0.f,    0.f,   -far / (far - near),          -(near * far) / (far - near)},
+                    {0.f,    0.f,   -1.f,                          0.f}};
+        else if constexpr (DepthRange == NDCDepthRange::NEGATIVE_ONE_TO_ONE)
+            return {{x_axis, 0.f,    0.f,                                  0.f},
+                    {0.f,    y_axis, 0.f,                                  0.f},
+                    {0.f,    0.f,   -(far + near) / (far - near),         -(2.f * near * far) / (far - near)},
+                    {0.f,    0.f,   -1.f,                                  0.f}};
+        else
+            std::unreachable();
+    }
     template<class Type = float, MatStoreType St = MatStoreType::ROW_MAJOR,
              NDCDepthRange DepthRange = NDCDepthRange::NEGATIVE_ONE_TO_ONE>
     [[nodiscard]]

source/engines/source_engine/formulas.cpp

@@ -38,25 +38,24 @@ namespace omath::source_engine
     Mat4X4 calc_perspective_projection_matrix(const float field_of_view, const float aspect_ratio, const float near,
                                               const float far, const NDCDepthRange ndc_depth_range) noexcept
     {
-        // NOTE: Need magic number to fix fov calculation, since source inherit Quake proj matrix calculation
+        // Source (inherited from Quake) stores FOV as horizontal FOV at a 4:3
-        constexpr auto k_multiply_factor = 0.75f;
+        // reference aspect. Convert to true vertical FOV, then delegate to the
-
+        // standard vertical-FOV left-handed builder with the caller's actual
-        const float fov_half_tan = std::tan(angles::degrees_to_radians(field_of_view) / 2.f) * k_multiply_factor;
+        // aspect ratio.
+        //   vfov = 2 · atan( tan(hfov_4:3 / 2) / (4/3) )
+        constexpr float k_source_reference_aspect = 4.f / 3.f;
+        const float half_hfov_4_3 = angles::degrees_to_radians(field_of_view) / 2.f;
+        const float vfov_deg = angles::radians_to_degrees(
+                2.f * std::atan(std::tan(half_hfov_4_3) / k_source_reference_aspect));
 
         if (ndc_depth_range == NDCDepthRange::ZERO_TO_ONE)
-            return {
+            return mat_perspective_left_handed<
-                    {1.f / (aspect_ratio * fov_half_tan), 0, 0, 0},
+                    float, MatStoreType::ROW_MAJOR, NDCDepthRange::ZERO_TO_ONE>(
-                    {0, 1.f / (fov_half_tan), 0, 0},
+                    vfov_deg, aspect_ratio, near, far);
-                    {0, 0, far / (far - near), -(near * far) / (far - near)},
-                    {0, 0, 1, 0},
-            };
         if (ndc_depth_range == NDCDepthRange::NEGATIVE_ONE_TO_ONE)
-            return {
+            return mat_perspective_left_handed<
-                    {1.f / (aspect_ratio * fov_half_tan), 0, 0, 0},
+                    float, MatStoreType::ROW_MAJOR, NDCDepthRange::NEGATIVE_ONE_TO_ONE>(
-                    {0, 1.f / (fov_half_tan), 0, 0},
+                    vfov_deg, aspect_ratio, near, far);
-                    {0, 0, (far + near) / (far - near), -(2.f * far * near) / (far - near)},
-                    {0, 0, 1, 0},
-            };
         std::unreachable();
     }
 } // namespace omath::source_engine

source/engines/unreal_engine/formulas.cpp

@@ -2,7 +2,6 @@
 // Created by Vlad on 3/22/2025.
 //
 #include "omath/engines/unreal_engine/formulas.hpp"
-
 namespace omath::unreal_engine
 {
     Vector3<float> forward_vector(const ViewAngles& angles) noexcept
@@ -25,22 +24,34 @@ namespace omath::unreal_engine
     }
     Mat4X4 calc_view_matrix(const ViewAngles& angles, const Vector3<float>& cam_origin) noexcept
     {
-        return mat_camera_view<float, MatStoreType::ROW_MAJOR>(forward_vector(angles), -right_vector(angles),
+        return mat_camera_view<float, MatStoreType::ROW_MAJOR>(forward_vector(angles), right_vector(angles),
                                                                up_vector(angles), cam_origin);
     }
     Mat4X4 rotation_matrix(const ViewAngles& angles) noexcept
     {
-        return mat_rotation_axis_x<float, MatStoreType::ROW_MAJOR>(angles.roll)
+        // UE FRotator is intrinsic Z-Y-X (Yaw → Pitch → Roll applied in local
-               * mat_rotation_axis_z<float, MatStoreType::ROW_MAJOR>(angles.yaw)
+        // frame), which for column-vector composition is Rz·Ry·Rx.
-               * mat_rotation_axis_y<float, MatStoreType::ROW_MAJOR>(-angles.pitch);
+        // Pitch and roll axes in omath spin opposite to UE's convention, so
+        // both carry a sign flip.
+        return mat_rotation_axis_z<float, MatStoreType::ROW_MAJOR>(angles.yaw)
+               * mat_rotation_axis_y<float, MatStoreType::ROW_MAJOR>(-angles.pitch)
+               * mat_rotation_axis_x<float, MatStoreType::ROW_MAJOR>(-angles.roll);
     }
+
+
     Mat4X4 calc_perspective_projection_matrix(const float field_of_view, const float aspect_ratio, const float near,
                                               const float far, const NDCDepthRange ndc_depth_range) noexcept
     {
+        // UE stores horizontal FOV in FMinimalViewInfo — use the left-handed
+        // horizontal-FOV builder directly.
         if (ndc_depth_range == NDCDepthRange::ZERO_TO_ONE)
-            return mat_perspective_left_handed<float, MatStoreType::ROW_MAJOR, NDCDepthRange::ZERO_TO_ONE>(
+            return mat_perspective_left_handed_horizontal_fov<
+                    float, MatStoreType::ROW_MAJOR, NDCDepthRange::ZERO_TO_ONE>(
                     field_of_view, aspect_ratio, near, far);
-
+        if (ndc_depth_range == NDCDepthRange::NEGATIVE_ONE_TO_ONE)
-        return mat_perspective_left_handed(field_of_view, aspect_ratio, near, far);
+            return mat_perspective_left_handed_horizontal_fov<
+                    float, MatStoreType::ROW_MAJOR, NDCDepthRange::NEGATIVE_ONE_TO_ONE>(
+                    field_of_view, aspect_ratio, near, far);
+        std::unreachable();
     }
 } // namespace omath::unreal_engine

tests/engines/unit_test_unreal_engine.cpp

@@ -44,7 +44,7 @@ TEST(unit_test_unreal_engine, ForwardVectorRotationRoll)
 {
     omath::unreal_engine::ViewAngles angles;
 
-    angles.roll = omath::unreal_engine::RollAngle::from_degrees(-90.f);
+    angles.roll = omath::unreal_engine::RollAngle::from_degrees(90.f);
 
     const auto forward = omath::unreal_engine::up_vector(angles);
     EXPECT_NEAR(forward.x, omath::unreal_engine::k_abs_right.x, 0.00001f);