learn-opengl/07-model-loading/src/model.cpp

#include "model.hpp"
#include "dbc.hpp"

unsigned int TextureFromFile(const std::string& path, const std::string& directory, bool gamma)
{
  std::string filename = path + "/" + filename;

  unsigned int textureID;
  glGenTextures(1, &textureID);

  int width = 0;
  int height = 0;
  int nrComponents = 0;

  unsigned char *data = stbi_load(filename.c_str(), &width, &height, &nrComponents, 0);
  dbc::check(data != nullptr, $F("Failed to load texture {}", filename));

  GLenum format = GL_RGB;

  if (nrComponents == 1) {
    format = GL_RED;
  } else if (nrComponents == 3) {
    format = GL_RGB;
  } else if (nrComponents == 4) {
    format = GL_RGBA;
  }

  glBindTexture(GL_TEXTURE_2D, textureID);
  glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);
  glGenerateMipmap(GL_TEXTURE_2D);

  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

  stbi_image_free(data);

  return textureID;
}

void Model::Draw(Shader &shader) {
  for(unsigned int i = 0; i < meshes.size(); i++) {
    meshes[i].Draw(shader);
  }
}

void Model::loadModel(std::string path) {
  Assimp::Importer importer;
  const aiScene* scene = importer.ReadFile(path, aiProcess_Triangulate | aiProcess_GenSmoothNormals | aiProcess_FlipUVs | aiProcess_CalcTangentSpace);

  dbc::check(scene != nullptr, "Assimp ReadFile return null");
  dbc::check(!(scene->mFlags & AI_SCENE_FLAGS_INCOMPLETE), "Assimp says incomplete.");
  dbc::check(scene->mRootNode != nullptr, "Assimp loaded scene doesn't have a root node");

  directory = path.substr(0, path.find_last_of('/'));

  processNode(scene->mRootNode, scene);
}

void Model::processNode(aiNode *node, const aiScene *scene) {
  for(unsigned int i = 0; i < node->mNumMeshes; i++) {
    aiMesh* mesh = scene->mMeshes[node->mMeshes[i]];
    meshes.push_back(processMesh(mesh, scene));
  }

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

Mesh Model::processMesh(aiMesh *mesh, const aiScene *scene) {
  std::vector<Vertex> vertices;
  std::vector<unsigned int> indices;
  std::vector<Texture> textures;

  for(unsigned int i = 0; i < mesh->mNumVertices; i++) {
    Vertex vertex;
    vertex.Position = glm::vec3(
      mesh->mVertices[i].x,
      mesh->mVertices[i].y,
      mesh->mVertices[i].z);

    if(mesh->HasNormals()) {
      vertex.Normal = glm::vec3(
        mesh->mNormals[i].x,
        mesh->mNormals[i].y,
        mesh->mNormals[i].z);
    }

    if(mesh->mTextureCoords[0]) {
      vertex.TexCoords = glm::vec2(
          mesh->mTextureCoords[0][i].x,
          mesh->mTextureCoords[0][i].y
      );
    } else {
      vertex.TexCoords = glm::vec2(0.0f, 0.0f);
    }

    vertices.push_back(vertex);
  }

  for(unsigned int i = 0; i < mesh->mNumFaces; i++) {
    aiFace face = mesh->mFaces[i];

    for(unsigned int j = 0; j < face.mNumIndices; j++) {
      indices.push_back(face.mIndices[j]);
    }
  }

  aiMaterial* material = scene->mMaterials[mesh->mMaterialIndex];

  // we assume a convention for sampler names in the shaders. Each diffuse texture should be named
  // as 'texture_diffuseN' where N is a sequential number ranging from 1 to MAX_SAMPLER_NUMBER.
  // Same applies to other texture as the following list summarizes:
  // diffuse: texture_diffuseN
  // specular: texture_specularN
  // normal: texture_normalN

  // 1. diffuse maps
  std::vector<Texture> diffuseMaps = loadMaterialTextures(material, aiTextureType_DIFFUSE, "texture_diffuse");
  textures.insert(textures.end(), diffuseMaps.begin(), diffuseMaps.end());

  // 2. specular maps
  std::vector<Texture> specularMaps = loadMaterialTextures(material, aiTextureType_SPECULAR, "texture_specular");
  textures.insert(textures.end(), specularMaps.begin(), specularMaps.end());

  // 3. normal maps
  std::vector<Texture> normalMaps = loadMaterialTextures(material, aiTextureType_HEIGHT, "texture_normal");
  textures.insert(textures.end(), normalMaps.begin(), normalMaps.end());

  // 4. height maps
  std::vector<Texture> heightMaps = loadMaterialTextures(material, aiTextureType_AMBIENT, "texture_height");
  textures.insert(textures.end(), heightMaps.begin(), heightMaps.end());

  return Mesh(vertices, indices, textures);
}

std::vector<Texture> Model::loadMaterialTextures(aiMaterial *mat, aiTextureType type, std::string typeName)
{
  std::vector<Texture> textures;
  for(unsigned int i = 0; i < mat->GetTextureCount(type); i++) {
    aiString str;
    mat->GetTexture(type, i, &str);
    std::string tx_str{str.C_Str()};

    bool skip = false;
    for(unsigned int j = 0; j < textures_loaded.size(); j++) {
      if(textures_loaded[j].path == tx_str) {
        textures.push_back(textures_loaded[j]);
        skip = true;
        break;
      }
    }

    if(!skip) {
      Texture texture{
        .id = TextureFromFile(tx_str, directory),
        .type = typeName,
        .path = tx_str,
      };

      textures.push_back(texture);
      textures_loaded.push_back(texture);
    }
  }

  return textures;
}