How we use Assimp in RayTrophi (open-source ray tracing engine with OptiX/Embree)

[maxkemal]

Hello everyone!

I'm developing an open-source ray tracing engine called RayTrophi which supports CPU acceleration, Embree, and OptiX.
We use Assimp extensively to import scenes, meshes, materials, cameras, lights, and animations.

Our custom class, AssimpLoader, wraps Assimp's functionality into a format usable by our ray tracing engine.

Here’s how we process nodes and convert them into triangles:

✅ Import geometry as individual triangles (Triangle class)
✅ Load materials and textures (albedo, roughness, metallic, normal, transmission, opacity, emission)
✅ Apply global transforms from Assimp’s node hierarchy
✅ For GPU rendering, assign material and texture bundles for OptiX backend
✅ Support for animations and bone weights

Key method (simplified from AssimpLoader.cpp):

static void processNodeToTriangles(aiNode* node, const aiScene* scene, std::vector<std::shared_ptr<Triangle>>& triangles, OptixGeometryData* geometry_data = nullptr) {
    aiMatrix4x4 globalTransform = getGlobalTransform(node);

    for (unsigned int i = 0; i < node->mNumMeshes; i++) {
        aiMesh* mesh = scene->mMeshes[node->mMeshes[i]];
        aiMaterial* material = scene->mMaterials[mesh->mMaterialIndex];

        // Material and GPU textures load
        auto convertedMaterial = processMaterial(material, scene, &hit_data, geometry_data);

        // Convert mesh to triangles
        processTriangles(mesh, globalTransform, node->mName.C_Str(), convertedMaterial, triangles);

        // Assign texture bundle to the last triangle
        if (!triangles.empty()) {
            auto& tri = triangles.back();
            tri->textureBundle = hit_data.textureBundle;  // Simplified
        }

        // For GPU (OptiX) add texture bundle
        if (geometry_data) {
            geometry_data->textures.push_back(hit_data.textureBundle);
        }
    }

    // Process children recursively
    for (unsigned int i = 0; i < node->mNumChildren; i++) {
        processNodeToTriangles(node->mChildren[i], scene, triangles, geometry_data);
    }
}

Why this might be useful for the Assimp community:

Shows how to convert Assimp’s scene graph to per-triangle data, including transformations.

Demonstrates real-world usage: material extraction, animation handling, GPU texture mapping.

Practical integration into a Monte Carlo ray tracing pipeline with Embree and OptiX.

GitHub Repository:
https://github.com/maxkemal/RayTrophi

We are happy to provide more examples (material property extraction, animation transforms, etc.) if anyone is interested.

Thank you to the Assimp team for maintaining such a versatile library!

[kimkulling]

Thank you so much for sharing this information. This helps us a lot getting a better understanding what do you as a cusomer of the Asset-Importer-Lib really need.