omath/docs/engines/unreal_engine/mesh_trait.md

omath::unreal_engine::MeshTrait — mesh transformation trait for Unreal Engine

Header: omath/engines/unreal_engine/traits/mesh_trait.hpp Namespace: omath::unreal_engine Purpose: provide Unreal Engine-specific rotation matrix computation for omath::primitives::Mesh

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Summary

MeshTrait is a trait class that provides the rotation_matrix function for transforming meshes in Unreal Engine's coordinate system. It serves as a template parameter to omath::primitives::Mesh, enabling engine-specific rotation behavior.

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Coordinate System

Unreal Engine uses:

• Up axis: +Z
• Forward axis: +X
• Right axis: +Y
• Handedness: Left-handed
• Rotation order: Roll (Y) → Pitch (X) → Yaw (Z)

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API

namespace omath::unreal_engine {

class MeshTrait final {
public:
    [[nodiscard]]
    static Mat4X4 rotation_matrix(const ViewAngles& rotation);
};

} // namespace omath::unreal_engine

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Method: rotation_matrix

static Mat4X4 rotation_matrix(const ViewAngles& rotation);

Computes a 4×4 rotation matrix from Unreal-style Euler angles.

Parameters:

• rotation — ViewAngles containing pitch, yaw, and roll angles

Returns: 4×4 rotation matrix suitable for mesh transformation

Implementation: Delegates to unreal_engine::rotation_matrix(rotation) defined in formulas.hpp.

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Usage

With Mesh

using namespace omath::unreal_engine;

// Create mesh (MeshTrait is used automatically)
Mesh my_mesh(vertices, indices);

// Set rotation using ViewAngles
ViewAngles angles;
angles.pitch = PitchAngle::from_degrees(30.0f);
angles.yaw = YawAngle::from_degrees(45.0f);
angles.roll = RollAngle::from_degrees(0.0f);

my_mesh.set_rotation(angles);

// The rotation matrix is computed using MeshTrait::rotation_matrix
auto matrix = my_mesh.get_to_world_matrix();

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Rotation Conventions

Unreal uses a left-handed Z-up coordinate system:

1. Roll (rotation around Y-axis / right axis)

   • Positive roll rotates forward axis upward
   • Range: [-180°, 180°]

2. Pitch (rotation around X-axis / forward axis)

   • Positive pitch looks upward
   • Range: typically [-89°, 89°]

3. Yaw (rotation around Z-axis / up axis)

   • Positive yaw rotates clockwise when viewed from above (left-handed)
   • Range: [-180°, 180°]

Note: Unreal applies rotations in Roll-Pitch-Yaw order, different from most other engines.

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Type Alias

namespace omath::unreal_engine {
    using Mesh = primitives::Mesh<Mat4X4, ViewAngles, MeshTrait, float>;
}

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See Also

• Mesh Documentation - Mesh primitive
• Formulas Documentation - Unreal rotation formula
• CameraTrait Documentation - Camera trait

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Last updated: 13 Nov 2025