b_engine/src/ModelLoader.cpp

//
// Created by lbmas on 4/29/2026.
//

#include <spdlog/spdlog.h>

#include "ModelLoader.h"

#include <assimp/Importer.hpp>
#include <assimp/postprocess.h>
#include <assimp/scene.h>

#include <cstring>

#include "glm/ext/matrix_transform.hpp"

std::unordered_map<std::string, std::shared_ptr<Model>> ModelLoader::models;

Mesh process_ai_mesh(aiMesh* aiMesh);
void process_ai_node(aiNode* node, const aiScene* scene, Model* model);

Material process_ai_material(aiMaterial* mat);

std::shared_ptr<Model> ModelLoader::load_from_file(std::string_view _path)
{
    Assimp::Importer importer;

    const aiScene* scene = importer.ReadFile(_path.data(),
                                             aiProcess_Triangulate |
                                             aiProcess_GenNormals |
                                             aiProcess_FlipUVs);

    if (!scene || scene->mFlags & AI_SCENE_FLAGS_INCOMPLETE || !scene->mRootNode)
    {
        spdlog::error("failed to load model {}: {}", _path, importer.GetErrorString());
        return nullptr;
    }

    auto model = std::make_shared<Model>();

    process_ai_node(scene->mRootNode, scene, model.get());

    return model;
}

void process_ai_node(aiNode* node, const aiScene* scene, glm::mat4 transform, Model* model)
{
    auto t = node->mTransformation;
    transform = transform * glm::mat4(nTransform)

    for (unsigned int i = 0; i < node->mNumMeshes; i++)
    {
        aiMesh* mesh = scene->mMeshes[node->mMeshes[i]];
        model->meshes.push_back(std::make_shared<Mesh>(process_ai_mesh(mesh)));
    }

    for (unsigned int i = 0; i < node->mNumChildren; i++)
    {
        process_ai_node(node->mChildren[i], scene, model);
    }
}

Mesh process_ai_mesh(aiMesh* aiMesh)
{
    auto positions = std::vector<float>(aiMesh->mNumVertices * 3);
    auto uvs = std::vector<float>(aiMesh->mNumVertices * 2);
    auto normals = std::vector<float>(aiMesh->mNumVertices * 3);
    auto indices = std::vector<unsigned int>();

    for (unsigned int i = 0; i < aiMesh->mNumVertices; i++)
    {
        auto position = aiMesh->mVertices[i];
        positions[3 * i] = position.x;
        positions[3 * i + 1] = position.y;
        positions[3 * i + 2] = position.z;

        if (aiMesh->HasNormals())
        {
            aiVector3D norm = aiMesh->mNormals[i];
            normals[3 * i]     = norm.x;
            normals[3 * i + 1] = norm.y;
            normals[3 * i + 2] = norm.z;
        }
        else
        {
            normals[3 * i] = 0;
            normals[3 * i + 1] = 0;
            normals[3 * i + 2] = 0;
        }

        if (aiMesh->HasTextureCoords(0))
        {
            uvs[2 * i] = aiMesh->mTextureCoords[0][i].x;
            uvs[2 * i + 1] = aiMesh->mTextureCoords[0][i].y;
        }
        else
        {
            uvs[2 * i] = 0;
            uvs[2 * i + 1] = 0;
        }
    }

    for(unsigned int i = 0; i < aiMesh->mNumFaces; i++)
    {
        const aiFace face = aiMesh->mFaces[i];
        for(unsigned int j = 0; j < face.mNumIndices; j++)
            indices.push_back(face.mIndices[j]);
    }

    return {positions, uvs, normals, indices};
}

Material process_ai_material(aiMaterial *mat) {
    aiString matName;
    aiReturn ret = mat->Get(AI_MATKEY_NAME, matName);
    if (ret != AI_SUCCESS) {
        spdlog::error("Could not find material name");
    }

    aiColor3D ambientColor {0.f, 0.f, 0.f};
    ret = mat->Get(AI_MATKEY_COLOR_DIFFUSE, ambientColor);
    if (ret != AI_SUCCESS) {
        spdlog::error("Could not find ambient color for material: {}", matName.C_Str());
        ambientColor = {.3f, .3f, .3f};
    }

    aiColor3D diffuseColor {1.f, 1.f, 1.f};
    ret = mat->Get(AI_MATKEY_COLOR_DIFFUSE, diffuseColor);
    if (ret != AI_SUCCESS) {
        spdlog::error("Could not find diffuse color for material: {}", matName.C_Str());
        diffuseColor = {1.f, 1.f, 1.f};
    }

    aiColor3D specularColor {1.f, 1.f, 1.f};
    ret = mat->Get(AI_MATKEY_COLOR_SPECULAR, specularColor);
    if (ret != AI_SUCCESS) {
        spdlog::error("Could not find specular color for material: {}", matName.C_Str());
        specularColor = {1.f, 1.f, 1.f};
    }

    float shininess = 32.f;
    ret = mat->Get(AI_MATKEY_SHININESS, shininess);
    if (ret != AI_SUCCESS) {
        spdlog::error("Could not find shininess for material: {}", matName.C_Str());
        shininess = 32.f;
    }

    Material material;
    material.name = matName.C_Str();
    material.phong.ambient = glm::vec3{ambientColor.r, ambientColor.g, ambientColor.b};
    material.phong.diffuse = glm::vec3{diffuseColor.r, diffuseColor.g, diffuseColor.b};
    material.phong.specular = glm::vec3{specularColor.r, specularColor.g, specularColor.b};
    material.phong.shininess = shininess;

    return material;
}